;************************************************************************
;** An Assembly File Listing to generate a 16K ROM for the ZX Spectrum **
;************************************************************************
; -------------------------
; Last updated: 13-DEC-2004
; -------------------------
; TASM cross-assembler directives.
; ( comment out, perhaps, for other assemblers - see Notes at end.)
#define DEFB .BYTE
#define DEFW .WORD
#define DEFM .TEXT
#define ORG .ORG
#define EQU .EQU
#define equ .EQU
; It is always a good idea to anchor, using ORGs, important sections such as
; the character bitmaps so that they don't move as code is added and removed.
; Generally most approaches try to maintain main entry points as they are
; often used by third-party software.
ORG 0000
;*****************************************
;** Part 1. RESTART ROUTINES AND TABLES **
;*****************************************
; -----------
; THE 'START'
; -----------
; At switch on, the Z80 chip is in Interrupt Mode 0.
; The Spectrum uses Interrupt Mode 1.
; This location can also be 'called' to reset the machine.
; Typically with PRINT USR 0.
;; START
L0000: DI ; Disable Interrupts.
XOR A ; Signal coming from START.
LD DE,$FFFF ; Set pointer to top of possible physical RAM.
JP L11CB ; Jump forward to common code at START-NEW.
; -------------------
; THE 'ERROR' RESTART
; -------------------
; The error pointer is made to point to the position of the error to enable
; the editor to highlight the error position if it occurred during syntax
; checking. It is used at 37 places in the program. An instruction fetch
; on address $0008 may page in a peripheral ROM such as the Sinclair
; Interface 1 or Disciple Disk Interface. This was not an original design
; concept and not all errors pass through here.
;; ERROR-1
L0008: LD HL,($5C5D) ; Fetch the character address from CH_ADD.
LD ($5C5F),HL ; Copy it to the error pointer X_PTR.
JR L0053 ; Forward to continue at ERROR-2.
; -----------------------------
; THE 'PRINT CHARACTER' RESTART
; -----------------------------
; The A register holds the code of the character that is to be sent to
; the output stream of the current channel. The alternate register set is
; used to output a character in the A register so there is no need to
; preserve any of the current main registers (HL, DE, BC).
; This restart is used 21 times.
;; PRINT-A
L0010: JP L15F2 ; Jump forward to continue at PRINT-A-2.
; ---
DEFB $FF, $FF, $FF ; Five unused locations.
DEFB $FF, $FF ;
; -------------------------------
; THE 'COLLECT CHARACTER' RESTART
; -------------------------------
; The contents of the location currently addressed by CH_ADD are fetched.
; A return is made if the value represents a character that has
; relevance to the BASIC parser. Otherwise CH_ADD is incremented and the
; tests repeated. CH_ADD will be addressing somewhere -
; 1) in the BASIC program area during line execution.
; 2) in workspace if evaluating, for example, a string expression.
; 3) in the edit buffer if parsing a direct command or a new BASIC line.
; 4) in workspace if accepting input but not that from INPUT LINE.
;; GET-CHAR
L0018: LD HL,($5C5D) ; fetch the address from CH_ADD.
LD A,(HL) ; use it to pick up current character.
;; TEST-CHAR
L001C: CALL L007D ; routine SKIP-OVER tests if the character is
; relevant.
RET NC ; Return if it is significant.
; ------------------------------------
; THE 'COLLECT NEXT CHARACTER' RESTART
; ------------------------------------
; As the BASIC commands and expressions are interpreted, this routine is
; called repeatedly to step along the line. It is used 83 times.
;; NEXT-CHAR
L0020: CALL L0074 ; routine CH-ADD+1 fetches the next immediate
; character.
JR L001C ; jump back to TEST-CHAR until a valid
; character is found.
; ---
DEFB $FF, $FF, $FF ; unused
; -----------------------
; THE 'CALCULATE' RESTART
; -----------------------
; This restart enters the Spectrum's internal, floating-point, stack-based,
; FORTH-like language.
; It is further used recursively from within the calculator.
; It is used on 77 occasions.
;; FP-CALC
L0028: JP L335B ; jump forward to the CALCULATE routine.
; ---
DEFB $FF, $FF, $FF ; spare - note that on the ZX81, space being a
DEFB $FF, $FF ; little cramped, these same locations were
; used for the five-byte end-calc literal.
; ------------------------------
; THE 'CREATE BC SPACES' RESTART
; ------------------------------
; This restart is used on only 12 occasions to create BC spaces
; between workspace and the calculator stack.
;; BC-SPACES
L0030: PUSH BC ; Save number of spaces.
LD HL,($5C61) ; Fetch WORKSP.
PUSH HL ; Save address of workspace.
JP L169E ; Jump forward to continuation code RESERVE.
; --------------------------------
; THE 'MASKABLE INTERRUPT' ROUTINE
; --------------------------------
; This routine increments the Spectrum's three-byte FRAMES counter fifty
; times a second (sixty times a second in the USA ).
; Both this routine and the called KEYBOARD subroutine use the IY register
; to access system variables and flags so a user-written program must
; disable interrupts to make use of the IY register.
;; MASK-INT
L0038: PUSH AF ; Save the registers that will be used but not
PUSH HL ; the IY register unfortunately.
LD HL,($5C78) ; Fetch the first two bytes at FRAMES1.
INC HL ; Increment lowest two bytes of counter.
LD ($5C78),HL ; Place back in FRAMES1.
LD A,H ; Test if the result was zero.
OR L ;
JR NZ,L0048 ; Forward, if not, to KEY-INT
INC (IY+$40) ; otherwise increment FRAMES3 the third byte.
; Now save the rest of the main registers and read and decode the keyboard.
;; KEY-INT
L0048: PUSH BC ; Save the other main registers.
PUSH DE ;
CALL L02BF ; Routine KEYBOARD executes a stage in the
; process of reading a key-press.
POP DE ;
POP BC ; Restore registers.
POP HL ;
POP AF ;
EI ; Enable Interrupts.
RET ; Return.
; ---------------------
; THE 'ERROR-2' ROUTINE
; ---------------------
; A continuation of the code at 0008.
; The error code is stored and after clearing down stacks, an indirect jump
; is made to MAIN-4, etc. to handle the error.
;; ERROR-2
L0053: POP HL ; drop the return address - the location
; after the RST 08H instruction.
LD L,(HL) ; fetch the error code that follows.
; (nice to see this instruction used.)
; Note. this entry point is used when out of memory at REPORT-4.
; The L register has been loaded with the report code but X-PTR is not
; updated.
;; ERROR-3
L0055: LD (IY+$00),L ; Store it in the system variable ERR_NR.
LD SP,($5C3D) ; ERR_SP points to an error handler on the
; machine stack. There may be a hierarchy
; of routines.
; To MAIN-4 initially at base.
; or REPORT-G on line entry.
; or ED-ERROR when editing.
; or ED-FULL during ed-enter.
; or IN-VAR-1 during runtime input etc.
JP L16C5 ; Jump to SET-STK to clear the calculator stack
; and reset MEM to usual place in the systems
; variables area and then indirectly to MAIN-4,
; etc.
; ---
DEFB $FF, $FF, $FF ; Unused locations
DEFB $FF, $FF, $FF ; before the fixed-position
DEFB $FF ; NMI routine.
; ------------------------------------
; THE 'NON-MASKABLE INTERRUPT' ROUTINE
; ------------------------------------
; 
; There is no NMI switch on the standard Spectrum or its peripherals.
; When the NMI line is held low, then no matter what the Z80 was doing at
; the time, it will now execute the code at 66 Hex.
; This Interrupt Service Routine will jump to location zero if the contents
; of the system variable NMIADD are zero or return if the location holds a
; non-zero address. So attaching a simple switch to the NMI as in the book
; "Spectrum Hardware Manual" causes a reset. The logic was obviously
; intended to work the other way. Sinclair Research said that, since they
; had never advertised the NMI, they had no plans to fix the error "until
; the opportunity arose".
;
; Note. The location NMIADD was, in fact, later used by Sinclair Research
; to enhance the text channel on the ZX Interface 1.
; On later Amstrad-made Spectrums, and the Brazilian Spectrum, the logic of
; this routine was indeed reversed but not as at first intended.
;
; It can be deduced by looking elsewhere in this ROM that the NMIADD system
; variable pointed to L121C and that this enabled a Warm Restart to be
; performed at any time, even while playing machine code games, or while
; another Spectrum has been allowed to gain control of this one.
;
; Software houses would have been able to protect their games from attack by
; placing two zeros in the NMIADD system variable.
;; RESET
L0066: PUSH AF ; save the
PUSH HL ; registers.
LD HL,($5CB0) ; fetch the system variable NMIADD.
LD A,H ; test address
OR L ; for zero.
JR NZ,L0070 ; skip to NO-RESET if NOT ZERO
JP (HL) ; jump to routine ( i.e. L0000 )
;; NO-RESET
L0070: POP HL ; restore the
POP AF ; registers.
RETN ; return to previous interrupt state.
; ---------------------------
; THE 'CH ADD + 1' SUBROUTINE
; ---------------------------
; This subroutine is called from RST 20, and three times from elsewhere
; to fetch the next immediate character following the current valid character
; address and update the associated system variable.
; The entry point TEMP-PTR1 is used from the SCANNING routine.
; Both TEMP-PTR1 and TEMP-PTR2 are used by the READ command routine.
;; CH-ADD+1
L0074: LD HL,($5C5D) ; fetch address from CH_ADD.
;; TEMP-PTR1
L0077: INC HL ; increase the character address by one.
;; TEMP-PTR2
L0078: LD ($5C5D),HL ; update CH_ADD with character address.
X007B: LD A,(HL) ; load character to A from HL.
RET ; and return.
; --------------------------
; THE 'SKIP OVER' SUBROUTINE
; --------------------------
; This subroutine is called once from RST 18 to skip over white-space and
; other characters irrelevant to the parsing of a BASIC line etc. .
; Initially the A register holds the character to be considered
; and HL holds its address which will not be within quoted text
; when a BASIC line is parsed.
; Although the 'tab' and 'at' characters will not appear in a BASIC line,
; they could be present in a string expression, and in other situations.
; Note. although white-space is usually placed in a program to indent loops
; and make it more readable, it can also be used for the opposite effect and
; spaces may appear in variable names although the parser never sees them.
; It is this routine that helps make the variables 'Anum bEr5 3BUS' and
; 'a number 53 bus' appear the same to the parser.
;; SKIP-OVER
L007D: CP $21 ; test if higher than space.
RET NC ; return with carry clear if so.
CP $0D ; carriage return ?
RET Z ; return also with carry clear if so.
; all other characters have no relevance
; to the parser and must be returned with
; carry set.
CP $10 ; test if 0-15d
RET C ; return, if so, with carry set.
CP $18 ; test if 24-32d
CCF ; complement carry flag.
RET C ; return with carry set if so.
; now leaves 16d-23d
INC HL ; all above have at least one extra character
; to be stepped over.
CP $16 ; controls 22d ('at') and 23d ('tab') have two.
JR C,L0090 ; forward to SKIPS with ink, paper, flash,
; bright, inverse or over controls.
; Note. the high byte of tab is for RS232 only.
; it has no relevance on this machine.
INC HL ; step over the second character of 'at'/'tab'.
;; SKIPS
L0090: SCF ; set the carry flag
LD ($5C5D),HL ; update the CH_ADD system variable.
RET ; return with carry set.
; ------------------
; THE 'TOKEN' TABLES
; ------------------
; The tokenized characters 134d (RND) to 255d (COPY) are expanded using
; this table. The last byte of a token is inverted to denote the end of
; the word. The first is an inverted step-over byte.
;; TKN-TABLE
L0095: DEFB '?'+$80
DEFM "RN"
DEFB 'D'+$80
DEFM "INKEY"
DEFB '$'+$80
DEFB 'P','I'+$80
DEFB 'F','N'+$80
DEFM "POIN"
DEFB 'T'+$80
DEFM "SCREEN"
DEFB '$'+$80
DEFM "ATT"
DEFB 'R'+$80
DEFB 'A','T'+$80
DEFM "TA"
DEFB 'B'+$80
DEFM "VAL"
DEFB '$'+$80
DEFM "COD"
DEFB 'E'+$80
DEFM "VA"
DEFB 'L'+$80
DEFM "LE"
DEFB 'N'+$80
DEFM "SI"
DEFB 'N'+$80
DEFM "CO"
DEFB 'S'+$80
DEFM "TA"
DEFB 'N'+$80
DEFM "AS"
DEFB 'N'+$80
DEFM "AC"
DEFB 'S'+$80
DEFM "AT"
DEFB 'N'+$80
DEFB 'L','N'+$80
DEFM "EX"
DEFB 'P'+$80
DEFM "IN"
DEFB 'T'+$80
DEFM "SQ"
DEFB 'R'+$80
DEFM "SG"
DEFB 'N'+$80
DEFM "AB"
DEFB 'S'+$80
DEFM "PEE"
DEFB 'K'+$80
DEFB 'I','N'+$80
DEFM "US"
DEFB 'R'+$80
DEFM "STR"
DEFB '$'+$80
DEFM "CHR"
DEFB '$'+$80
DEFM "NO"
DEFB 'T'+$80
DEFM "BI"
DEFB 'N'+$80
; The previous 32 function-type words are printed without a leading space
; The following have a leading space if they begin with a letter
DEFB 'O','R'+$80
DEFM "AN"
DEFB 'D'+$80
DEFB $3C,'='+$80 ; <=
DEFB $3E,'='+$80 ; >=
DEFB $3C,$3E+$80 ; <>
DEFM "LIN"
DEFB 'E'+$80
DEFM "THE"
DEFB 'N'+$80
DEFB 'T','O'+$80
DEFM "STE"
DEFB 'P'+$80
DEFM "DEF F"
DEFB 'N'+$80
DEFM "CA"
DEFB 'T'+$80
DEFM "FORMA"
DEFB 'T'+$80
DEFM "MOV"
DEFB 'E'+$80
DEFM "ERAS"
DEFB 'E'+$80
DEFM "OPEN "
DEFB '#'+$80
DEFM "CLOSE "
DEFB '#'+$80
DEFM "MERG"
DEFB 'E'+$80
DEFM "VERIF"
DEFB 'Y'+$80
DEFM "BEE"
DEFB 'P'+$80
DEFM "CIRCL"
DEFB 'E'+$80
DEFM "IN"
DEFB 'K'+$80
DEFM "PAPE"
DEFB 'R'+$80
DEFM "FLAS"
DEFB 'H'+$80
DEFM "BRIGH"
DEFB 'T'+$80
DEFM "INVERS"
DEFB 'E'+$80
DEFM "OVE"
DEFB 'R'+$80
DEFM "OU"
DEFB 'T'+$80
DEFM "LPRIN"
DEFB 'T'+$80
DEFM "LLIS"
DEFB 'T'+$80
DEFM "STO"
DEFB 'P'+$80
DEFM "REA"
DEFB 'D'+$80
DEFM "DAT"
DEFB 'A'+$80
DEFM "RESTOR"
DEFB 'E'+$80
DEFM "NE"
DEFB 'W'+$80
DEFM "BORDE"
DEFB 'R'+$80
DEFM "CONTINU"
DEFB 'E'+$80
DEFM "DI"
DEFB 'M'+$80
DEFM "RE"
DEFB 'M'+$80
DEFM "FO"
DEFB 'R'+$80
DEFM "GO T"
DEFB 'O'+$80
DEFM "GO SU"
DEFB 'B'+$80
DEFM "INPU"
DEFB 'T'+$80
DEFM "LOA"
DEFB 'D'+$80
DEFM "LIS"
DEFB 'T'+$80
DEFM "LE"
DEFB 'T'+$80
DEFM "PAUS"
DEFB 'E'+$80
DEFM "NEX"
DEFB 'T'+$80
DEFM "POK"
DEFB 'E'+$80
DEFM "PRIN"
DEFB 'T'+$80
DEFM "PLO"
DEFB 'T'+$80
DEFM "RU"
DEFB 'N'+$80
DEFM "SAV"
DEFB 'E'+$80
DEFM "RANDOMIZ"
DEFB 'E'+$80
DEFB 'I','F'+$80
DEFM "CL"
DEFB 'S'+$80
DEFM "DRA"
DEFB 'W'+$80
DEFM "CLEA"
DEFB 'R'+$80
DEFM "RETUR"
DEFB 'N'+$80
DEFM "COP"
DEFB 'Y'+$80
; ----------------
; THE 'KEY' TABLES
; ----------------
; These six look-up tables are used by the keyboard reading routine
; to decode the key values.
;
; The first table contains the maps for the 39 keys of the standard
; 40-key Spectrum keyboard. The remaining key [SHIFT $27] is read directly.
; The keys consist of the 26 upper-case alphabetic characters, the 10 digit
; keys and the space, ENTER and symbol shift key.
; Unshifted alphabetic keys have $20 added to the value.
; The keywords for the main alphabetic keys are obtained by adding $A5 to
; the values obtained from this table.
;; MAIN-KEYS
L0205: DEFB $42 ; B
DEFB $48 ; H
DEFB $59 ; Y
DEFB $36 ; 6
DEFB $35 ; 5
DEFB $54 ; T
DEFB $47 ; G
DEFB $56 ; V
DEFB $4E ; N
DEFB $4A ; J
DEFB $55 ; U
DEFB $37 ; 7
DEFB $34 ; 4
DEFB $52 ; R
DEFB $46 ; F
DEFB $43 ; C
DEFB $4D ; M
DEFB $4B ; K
DEFB $49 ; I
DEFB $38 ; 8
DEFB $33 ; 3
DEFB $45 ; E
DEFB $44 ; D
DEFB $58 ; X
DEFB $0E ; SYMBOL SHIFT
DEFB $4C ; L
DEFB $4F ; O
DEFB $39 ; 9
DEFB $32 ; 2
DEFB $57 ; W
DEFB $53 ; S
DEFB $5A ; Z
DEFB $20 ; SPACE
DEFB $0D ; ENTER
DEFB $50 ; P
DEFB $30 ; 0
DEFB $31 ; 1
DEFB $51 ; Q
DEFB $41 ; A
;; E-UNSHIFT
; The 26 unshifted extended mode keys for the alphabetic characters.
; The green keywords on the original keyboard.
L022C: DEFB $E3 ; READ
DEFB $C4 ; BIN
DEFB $E0 ; LPRINT
DEFB $E4 ; DATA
DEFB $B4 ; TAN
DEFB $BC ; SGN
DEFB $BD ; ABS
DEFB $BB ; SQR
DEFB $AF ; CODE
DEFB $B0 ; VAL
DEFB $B1 ; LEN
DEFB $C0 ; USR
DEFB $A7 ; PI
DEFB $A6 ; INKEY$
DEFB $BE ; PEEK
DEFB $AD ; TAB
DEFB $B2 ; SIN
DEFB $BA ; INT
DEFB $E5 ; RESTORE
DEFB $A5 ; RND
DEFB $C2 ; CHR$
DEFB $E1 ; LLIST
DEFB $B3 ; COS
DEFB $B9 ; EXP
DEFB $C1 ; STR$
DEFB $B8 ; LN
;; EXT-SHIFT
; The 26 shifted extended mode keys for the alphabetic characters.
; The red keywords below keys on the original keyboard.
L0246: DEFB $7E ; ~
DEFB $DC ; BRIGHT
DEFB $DA ; PAPER
DEFB $5C ; \
DEFB $B7 ; ATN
DEFB $7B ; {
DEFB $7D ; }
DEFB $D8 ; CIRCLE
DEFB $BF ; IN
DEFB $AE ; VAL$
DEFB $AA ; SCREEN$
DEFB $AB ; ATTR
DEFB $DD ; INVERSE
DEFB $DE ; OVER
DEFB $DF ; OUT
DEFB $7F ; (Copyright character)
DEFB $B5 ; ASN
DEFB $D6 ; VERIFY
DEFB $7C ; |
DEFB $D5 ; MERGE
DEFB $5D ; ]
DEFB $DB ; FLASH
DEFB $B6 ; ACS
DEFB $D9 ; INK
DEFB $5B ; [
DEFB $D7 ; BEEP
;; CTL-CODES
; The ten control codes assigned to the top line of digits when the shift
; key is pressed.
L0260: DEFB $0C ; DELETE
DEFB $07 ; EDIT
DEFB $06 ; CAPS LOCK
DEFB $04 ; TRUE VIDEO
DEFB $05 ; INVERSE VIDEO
DEFB $08 ; CURSOR LEFT
DEFB $0A ; CURSOR DOWN
DEFB $0B ; CURSOR UP
DEFB $09 ; CURSOR RIGHT
DEFB $0F ; GRAPHICS
;; SYM-CODES
; The 26 red symbols assigned to the alphabetic characters of the keyboard.
; The ten single-character digit symbols are converted without the aid of
; a table using subtraction and minor manipulation.
L026A: DEFB $E2 ; STOP
DEFB $2A ; *
DEFB $3F ; ?
DEFB $CD ; STEP
DEFB $C8 ; >=
DEFB $CC ; TO
DEFB $CB ; THEN
DEFB $5E ; ^
DEFB $AC ; AT
DEFB $2D ; -
DEFB $2B ; +
DEFB $3D ; =
DEFB $2E ; .
DEFB $2C ; ,
DEFB $3B ; ;
DEFB $22 ; "
DEFB $C7 ; <=
DEFB $3C ; <
DEFB $C3 ; NOT
DEFB $3E ; >
DEFB $C5 ; OR
DEFB $2F ; /
DEFB $C9 ; <>
DEFB $60 ; pound
DEFB $C6 ; AND
DEFB $3A ; :
;; E-DIGITS
; The ten keywords assigned to the digits in extended mode.
; The remaining red keywords below the keys.
L0284: DEFB $D0 ; FORMAT
DEFB $CE ; DEF FN
DEFB $A8 ; FN
DEFB $CA ; LINE
DEFB $D3 ; OPEN #
DEFB $D4 ; CLOSE #
DEFB $D1 ; MOVE
DEFB $D2 ; ERASE
DEFB $A9 ; POINT
DEFB $CF ; CAT
;*******************************
;** Part 2. KEYBOARD ROUTINES **
;*******************************
; Using shift keys and a combination of modes the Spectrum 40-key keyboard
; can be mapped to 256 input characters
; ---------------------------------------------------------------------------
;
; 0 1 2 3 4 -Bits- 4 3 2 1 0
; PORT PORT
;
; F7FE [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] | [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 0 ] EFFE
; ^ | v
; FBFE [ Q ] [ W ] [ E ] [ R ] [ T ] | [ Y ] [ U ] [ I ] [ O ] [ P ] DFFE
; ^ | v
; FDFE [ A ] [ S ] [ D ] [ F ] [ G ] | [ H ] [ J ] [ K ] [ L ] [ ENT ] BFFE
; ^ | v
; FEFE [SHI] [ Z ] [ X ] [ C ] [ V ] | [ B ] [ N ] [ M ] [sym] [ SPC ] 7FFE
; ^ $27 $18 v
; Start End
; 00100111 00011000
;
; ---------------------------------------------------------------------------
; The above map may help in reading.
; The neat arrangement of ports means that the B register need only be
; rotated left to work up the left hand side and then down the right
; hand side of the keyboard. When the reset bit drops into the carry
; then all 8 half-rows have been read. Shift is the first key to be
; read. The lower six bits of the shifts are unambiguous.
; -------------------------------
; THE 'KEYBOARD SCANNING' ROUTINE
; -------------------------------
; From keyboard and s-inkey$
; Returns 1 or 2 keys in DE, most significant shift first if any
; key values 0-39 else 255
;; KEY-SCAN
L028E: LD L,$2F ; initial key value
; valid values are obtained by subtracting
; eight five times.
LD DE,$FFFF ; a buffer to receive 2 keys.
LD BC,$FEFE ; the commencing port address
; B holds 11111110 initially and is also
; used to count the 8 half-rows
;; KEY-LINE
L0296: IN A,(C) ; read the port to A - bits will be reset
; if a key is pressed else set.
CPL ; complement - pressed key-bits are now set
AND $1F ; apply 00011111 mask to pick up the
; relevant set bits.
JR Z,L02AB ; forward to KEY-DONE if zero and therefore
; no keys pressed in row at all.
LD H,A ; transfer row bits to H
LD A,L ; load the initial key value to A
;; KEY-3KEYS
L029F: INC D ; now test the key buffer
RET NZ ; if we have collected 2 keys already
; then too many so quit.
;; KEY-BITS
L02A1: SUB $08 ; subtract 8 from the key value
; cycling through key values (top = $27)
; e.g. 2F> 27>1F>17>0F>07
; 2E> 26>1E>16>0E>06
SRL H ; shift key bits right into carry.
JR NC,L02A1 ; back to KEY-BITS if not pressed
; but if pressed we have a value (0-39d)
LD D,E ; transfer a possible previous key to D
LD E,A ; transfer the new key to E
JR NZ,L029F ; back to KEY-3KEYS if there were more
; set bits - H was not yet zero.
;; KEY-DONE
L02AB: DEC L ; cycles 2F>2E>2D>2C>2B>2A>29>28 for
; each half-row.
RLC B ; form next port address e.g. FEFE > FDFE
JR C,L0296 ; back to KEY-LINE if still more rows to do.
LD A,D ; now test if D is still FF ?
INC A ; if it is zero we have at most 1 key
; range now $01-$28 (1-40d)
RET Z ; return if one key or no key.
CP $28 ; is it capsshift (was $27) ?
RET Z ; return if so.
CP $19 ; is it symbol shift (was $18) ?
RET Z ; return also
LD A,E ; now test E
LD E,D ; but first switch
LD D,A ; the two keys.
CP $18 ; is it symbol shift ?
RET ; return (with zero set if it was).
; but with symbol shift now in D
; ----------------------
; THE 'KEYBOARD' ROUTINE
; ----------------------
; Called from the interrupt 50 times a second.
;
;; KEYBOARD
L02BF: CALL L028E ; routine KEY-SCAN
RET NZ ; return if invalid combinations
; then decrease the counters within the two key-state maps
; as this could cause one to become free.
; if the keyboard has not been pressed during the last five interrupts
; then both sets will be free.
LD HL,$5C00 ; point to KSTATE-0
;; K-ST-LOOP
L02C6: BIT 7,(HL) ; is it free ? (i.e. $FF)
JR NZ,L02D1 ; forward to K-CH-SET if so
INC HL ; address the 5-counter
DEC (HL) ; decrease the counter
DEC HL ; step back
JR NZ,L02D1 ; forward to K-CH-SET if not at end of count
LD (HL),$FF ; else mark this particular map free.
;; K-CH-SET
L02D1: LD A,L ; make a copy of the low address byte.
LD HL,$5C04 ; point to KSTATE-4
; (ld l,$04 would do)
CP L ; have both sets been considered ?
JR NZ,L02C6 ; back to K-ST-LOOP to consider this 2nd set
; now the raw key (0-38d) is converted to a main key (uppercase).
CALL L031E ; routine K-TEST to get main key in A
RET NC ; return if just a single shift
LD HL,$5C00 ; point to KSTATE-0
CP (HL) ; does the main key code match ?
JR Z,L0310 ; forward to K-REPEAT if so
; if not consider the second key map.
EX DE,HL ; save kstate-0 in de
LD HL,$5C04 ; point to KSTATE-4
CP (HL) ; does the main key code match ?
JR Z,L0310 ; forward to K-REPEAT if so
; having excluded a repeating key we can now consider a new key.
; the second set is always examined before the first.
BIT 7,(HL) ; is the key map free ?
JR NZ,L02F1 ; forward to K-NEW if so.
EX DE,HL ; bring back KSTATE-0
BIT 7,(HL) ; is it free ?
RET Z ; return if not.
; as we have a key but nowhere to put it yet.
; continue or jump to here if one of the buffers was free.
;; K-NEW
L02F1: LD E,A ; store key in E
LD (HL),A ; place in free location
INC HL ; advance to the interrupt counter
LD (HL),$05 ; and initialize counter to 5
INC HL ; advance to the delay
LD A,($5C09) ; pick up the system variable REPDEL
LD (HL),A ; and insert that for first repeat delay.
INC HL ; advance to last location of state map.
LD C,(IY+$07) ; pick up MODE (3 bytes)
LD D,(IY+$01) ; pick up FLAGS (3 bytes)
PUSH HL ; save state map location
; Note. could now have used, to avoid IY,
; ld l,$41; ld c,(hl); ld l,$3B; ld d,(hl).
; six and two threes of course.
CALL L0333 ; routine K-DECODE
POP HL ; restore map pointer
LD (HL),A ; put the decoded key in last location of map.
;; K-END
L0308: LD ($5C08),A ; update LASTK system variable.
SET 5,(IY+$01) ; update FLAGS - signal a new key.
RET ; return to interrupt routine.
; -----------------------
; THE 'REPEAT KEY' BRANCH
; -----------------------
; A possible repeat has been identified. HL addresses the raw key.
; The last location of the key map holds the decoded key from the first
; context. This could be a keyword and, with the exception of NOT a repeat
; is syntactically incorrect and not really desirable.
;; K-REPEAT
L0310: INC HL ; increment the map pointer to second location.
LD (HL),$05 ; maintain interrupt counter at 5.
INC HL ; now point to third location.
DEC (HL) ; decrease the REPDEL value which is used to
; time the delay of a repeat key.
RET NZ ; return if not yet zero.
LD A,($5C0A) ; fetch the system variable value REPPER.
LD (HL),A ; for subsequent repeats REPPER will be used.
INC HL ; advance
;
LD A,(HL) ; pick up the key decoded possibly in another
; context.
; Note. should compare with $A5 (RND) and make
; a simple return if this is a keyword.
; e.g. cp $a5; ret nc; (3 extra bytes)
JR L0308 ; back to K-END
; ----------------------
; THE 'KEY-TEST' ROUTINE
; ----------------------
; also called from s-inkey$
; begin by testing for a shift with no other.
;; K-TEST
L031E: LD B,D ; load most significant key to B
; will be $FF if not shift.
LD D,$00 ; and reset D to index into main table
LD A,E ; load least significant key from E
CP $27 ; is it higher than 39d i.e. FF
RET NC ; return with just a shift (in B now)
CP $18 ; is it symbol shift ?
JR NZ,L032C ; forward to K-MAIN if not
; but we could have just symbol shift and no other
BIT 7,B ; is other key $FF (ie not shift)
RET NZ ; return with solitary symbol shift
;; K-MAIN
L032C: LD HL,L0205 ; address: MAIN-KEYS
ADD HL,DE ; add offset 0-38
LD A,(HL) ; pick up main key value
SCF ; set carry flag
RET ; return (B has other key still)
; ----------------------------------
; THE 'KEYBOARD DECODING' SUBROUTINE
; ----------------------------------
; also called from s-inkey$
;; K-DECODE
L0333: LD A,E ; pick up the stored main key
CP $3A ; an arbitrary point between digits and letters
JR C,L0367 ; forward to K-DIGIT with digits, space, enter.
DEC C ; decrease MODE ( 0='KLC', 1='E', 2='G')
JP M,L034F ; to K-KLC-LET if was zero
JR Z,L0341 ; to K-E-LET if was 1 for extended letters.
; proceed with graphic codes.
; Note. should selectively drop return address if code > 'U' ($55).
; i.e. abort the KEYBOARD call.
; e.g. cp 'V'; jr c,addit; pop af ;pop af ;;addit etc. (6 extra bytes).
; (s-inkey$ never gets into graphics mode.)
;; addit
ADD A,$4F ; add offset to augment 'A' to graphics A say.
RET ; return.
; Note. ( but [GRAPH] V gives RND, etc ).
; ---
; the jump was to here with extended mode with uppercase A-Z.
;; K-E-LET
L0341: LD HL,L022C-$41 ; base address of E-UNSHIFT L022c.
; ( $01EB in standard ROM ).
INC B ; test B is it empty i.e. not a shift.
JR Z,L034A ; forward to K-LOOK-UP if neither shift.
LD HL,L0246-$41 ; Address: $0205 L0246-$41 EXT-SHIFT base
;; K-LOOK-UP
L034A: LD D,$00 ; prepare to index.
ADD HL,DE ; add the main key value.
LD A,(HL) ; pick up other mode value.
RET ; return.
; ---
; the jump was here with mode = 0
;; K-KLC-LET
L034F: LD HL,L026A-$41 ; prepare base of sym-codes
BIT 0,B ; shift=$27 sym-shift=$18
JR Z,L034A ; back to K-LOOK-UP with symbol-shift
BIT 3,D ; test FLAGS is it 'K' mode (from OUT-CURS)
JR Z,L0364 ; skip to K-TOKENS if so
BIT 3,(IY+$30) ; test FLAGS2 - consider CAPS LOCK ?
RET NZ ; return if so with main code.
INC B ; is shift being pressed ?
; result zero if not
RET NZ ; return if shift pressed.
ADD A,$20 ; else convert the code to lower case.
RET ; return.
; ---
; the jump was here for tokens
;; K-TOKENS
L0364: ADD A,$A5 ; add offset to main code so that 'A'
; becomes 'NEW' etc.
RET ; return.
; ---
; the jump was here with digits, space, enter and symbol shift (< $xx)
;; K-DIGIT
L0367: CP $30 ; is it '0' or higher ?
RET C ; return with space, enter and symbol-shift
DEC C ; test MODE (was 0='KLC', 1='E', 2='G')
JP M,L039D ; jump to K-KLC-DGT if was 0.
JR NZ,L0389 ; forward to K-GRA-DGT if mode was 2.
; continue with extended digits 0-9.
LD HL,L0284-$30 ; $0254 - base of E-DIGITS
BIT 5,B ; test - shift=$27 sym-shift=$18
JR Z,L034A ; to K-LOOK-UP if sym-shift
CP $38 ; is character '8' ?
JR NC,L0382 ; to K-8-&-9 if greater than '7'
SUB $20 ; reduce to ink range $10-$17
INC B ; shift ?
RET Z ; return if not.
ADD A,$08 ; add 8 to give paper range $18 - $1F
RET ; return
; ---
; 89
;; K-8-&-9
L0382: SUB $36 ; reduce to 02 and 03 bright codes
INC B ; test if shift pressed.
RET Z ; return if not.
ADD A,$FE ; subtract 2 setting carry
RET ; to give 0 and 1 flash codes.
; ---
; graphics mode with digits
;; K-GRA-DGT
L0389: LD HL,L0260-$30 ; $0230 base address of CTL-CODES
CP $39 ; is key '9' ?
JR Z,L034A ; back to K-LOOK-UP - changed to $0F, GRAPHICS.
CP $30 ; is key '0' ?
JR Z,L034A ; back to K-LOOK-UP - changed to $0C, delete.
; for keys '0' - '7' we assign a mosaic character depending on shift.
AND $07 ; convert character to number. 0 - 7.
ADD A,$80 ; add offset - they start at $80
INC B ; destructively test for shift
RET Z ; and return if not pressed.
XOR $0F ; toggle bits becomes range $88-$8F
RET ; return.
; ---
; now digits in 'KLC' mode
;; K-KLC-DGT
L039D: INC B ; return with digit codes if neither
RET Z ; shift key pressed.
BIT 5,B ; test for caps shift.
LD HL,L0260-$30 ; prepare base of table CTL-CODES.
JR NZ,L034A ; back to K-LOOK-UP if shift pressed.
; must have been symbol shift
SUB $10 ; for ASCII most will now be correct
; on a standard typewriter.
CP $22 ; but '@' is not - see below.
JR Z,L03B2 ; forward to K-@-CHAR if so
CP $20 ; '_' is the other one that fails
RET NZ ; return if not.
LD A,$5F ; substitute ASCII '_'
RET ; return.
; ---
;; K-@-CHAR
L03B2: LD A,$40 ; substitute ASCII '@'
RET ; return.
; ------------------------------------------------------------------------
; The Spectrum Input character keys. One or two are abbreviated.
; From $00 Flash 0 to $FF COPY. The routine above has decoded all these.
; | 00 Fl0| 01 Fl1| 02 Br0| 03 Br1| 04 In0| 05 In1| 06 CAP| 07 EDT|
; | 08 LFT| 09 RIG| 0A DWN| 0B UP | 0C DEL| 0D ENT| 0E SYM| 0F GRA|
; | 10 Ik0| 11 Ik1| 12 Ik2| 13 Ik3| 14 Ik4| 15 Ik5| 16 Ik6| 17 Ik7|
; | 18 Pa0| 19 Pa1| 1A Pa2| 1B Pa3| 1C Pa4| 1D Pa5| 1E Pa6| 1F Pa7|
; | 20 SP | 21 ! | 22 " | 23 # | 24 $ | 25 % | 26 & | 27 ' |
; | 28 ( | 29 ) | 2A * | 2B + | 2C , | 2D - | 2E . | 2F / |
; | 30 0 | 31 1 | 32 2 | 33 3 | 34 4 | 35 5 | 36 6 | 37 7 |
; | 38 8 | 39 9 | 3A : | 3B ; | 3C < | 3D = | 3E > | 3F ? |
; | 40 @ | 41 A | 42 B | 43 C | 44 D | 45 E | 46 F | 47 G |
; | 48 H | 49 I | 4A J | 4B K | 4C L | 4D M | 4E N | 4F O |
; | 50 P | 51 Q | 52 R | 53 S | 54 T | 55 U | 56 V | 57 W |
; | 58 X | 59 Y | 5A Z | 5B [ | 5C \ | 5D ] | 5E ^ | 5F _ |
; | 60 £ | 61 a | 62 b | 63 c | 64 d | 65 e | 66 f | 67 g |
; | 68 h | 69 i | 6A j | 6B k | 6C l | 6D m | 6E n | 6F o |
; | 70 p | 71 q | 72 r | 73 s | 74 t | 75 u | 76 v | 77 w |
; | 78 x | 79 y | 7A z | 7B { | 7C | | 7D } | 7E ~ | 7F © |
; | 80 128| 81 129| 82 130| 83 131| 84 132| 85 133| 86 134| 87 135|
; | 88 136| 89 137| 8A 138| 8B 139| 8C 140| 8D 141| 8E 142| 8F 143|
; | 90 [A]| 91 [B]| 92 [C]| 93 [D]| 94 [E]| 95 [F]| 96 [G]| 97 [H]|
; | 98 [I]| 99 [J]| 9A [K]| 9B [L]| 9C [M]| 9D [N]| 9E [O]| 9F [P]|
; | A0 [Q]| A1 [R]| A2 [S]| A3 [T]| A4 [U]| A5 RND| A6 IK$| A7 PI |
; | A8 FN | A9 PNT| AA SC$| AB ATT| AC AT | AD TAB| AE VL$| AF COD|
; | B0 VAL| B1 LEN| B2 SIN| B3 COS| B4 TAN| B5 ASN| B6 ACS| B7 ATN|
; | B8 LN | B9 EXP| BA INT| BB SQR| BC SGN| BD ABS| BE PEK| BF IN |
; | C0 USR| C1 ST$| C2 CH$| C3 NOT| C4 BIN| C5 OR | C6 AND| C7 <= |
; | C8 >= | C9 <> | CA LIN| CB THN| CC TO | CD STP| CE DEF| CF CAT|
; | D0 FMT| D1 MOV| D2 ERS| D3 OPN| D4 CLO| D5 MRG| D6 VFY| D7 BEP|
; | D8 CIR| D9 INK| DA PAP| DB FLA| DC BRI| DD INV| DE OVR| DF OUT|
; | E0 LPR| E1 LLI| E2 STP| E3 REA| E4 DAT| E5 RES| E6 NEW| E7 BDR|
; | E8 CON| E9 DIM| EA REM| EB FOR| EC GTO| ED GSB| EE INP| EF LOA|
; | F0 LIS| F1 LET| F2 PAU| F3 NXT| F4 POK| F5 PRI| F6 PLO| F7 RUN|
; | F8 SAV| F9 RAN| FA IF | FB CLS| FC DRW| FD CLR| FE RET| FF CPY|
; Note that for simplicity, Sinclair have located all the control codes
; below the space character.
; ASCII DEL, $7F, has been made a copyright symbol.
; Also $60, '`', not used in BASIC but used in other languages, has been
; allocated the local currency symbol for the relevant country -
; £ in most Spectrums.
; ------------------------------------------------------------------------
;**********************************
;** Part 3. LOUDSPEAKER ROUTINES **
;**********************************
; Documented by Alvin Albrecht.
; ------------------------------
; Routine to control loudspeaker
; ------------------------------
; Outputs a square wave of given duration and frequency
; to the loudspeaker.
; Enter with: DE = #cycles - 1
; HL = tone period as described next
;
; The tone period is measured in T states and consists of
; three parts: a coarse part (H register), a medium part
; (bits 7..2 of L) and a fine part (bits 1..0 of L) which
; contribute to the waveform timing as follows:
;
; coarse medium fine
; duration of low = 118 + 1024*H + 16*(L>>2) + 4*(L&0x3)
; duration of hi = 118 + 1024*H + 16*(L>>2) + 4*(L&0x3)
; Tp = tone period = 236 + 2048*H + 32*(L>>2) + 8*(L&0x3)
; = 236 + 2048*H + 8*L = 236 + 8*HL
;
; As an example, to output five seconds of middle C (261.624 Hz):
; (a) Tone period = 1/261.624 = 3.822ms
; (b) Tone period in T-States = 3.822ms*fCPU = 13378
; where fCPU = clock frequency of the CPU = 3.5MHz
; © Find H and L for desired tone period:
; HL = (Tp - 236) / 8 = (13378 - 236) / 8 = 1643 = 0x066B
; (d) Tone duration in cycles = 5s/3.822ms = 1308 cycles
; DE = 1308 - 1 = 0x051B
;
; The resulting waveform has a duty ratio of exactly 50%.
;
;
;; BEEPER
L03B5: DI ; Disable Interrupts so they don't disturb timing
LD A,L ;
SRL L ;
SRL L ; L = medium part of tone period
CPL ;
AND $03 ; A = 3 - fine part of tone period
LD C,A ;
LD B,$00 ;
LD IX,L03D1 ; Address: BE-IX+3
ADD IX,BC ; IX holds address of entry into the loop
; the loop will contain 0-3 NOPs, implementing
; the fine part of the tone period.
LD A,($5C48) ; BORDCR
AND $38 ; bits 5..3 contain border colour
RRCA ; border colour bits moved to 2..0
RRCA ; to match border bits on port #FE
RRCA ;
OR $08 ; bit 3 set (tape output bit on port #FE)
; for loud sound output
;; BE-IX+3
L03D1: NOP ;(4) ; optionally executed NOPs for small
; adjustments to tone period
;; BE-IX+2
L03D2: NOP ;(4) ;
;; BE-IX+1
L03D3: NOP ;(4) ;
;; BE-IX+0
L03D4: INC B ;(4) ;
INC C ;(4) ;
;; BE-H&L-LP
L03D6: DEC C ;(4) ; timing loop for duration of
JR NZ,L03D6 ;(12/7); high or low pulse of waveform
LD C,$3F ;(7) ;
DEC B ;(4) ;
JP NZ,L03D6 ;(10) ; to BE-H&L-LP
XOR $10 ;(7) ; toggle output beep bit
OUT ($FE),A ;(11) ; output pulse
LD B,H ;(4) ; B = coarse part of tone period
LD C,A ;(4) ; save port #FE output byte
BIT 4,A ;(8) ; if new output bit is high, go
JR NZ,L03F2 ;(12/7); to BE-AGAIN
LD A,D ;(4) ; one cycle of waveform has completed
OR E ;(4) ; (low->low). if cycle countdown = 0
JR Z,L03F6 ;(12/7); go to BE-END
LD A,C ;(4) ; restore output byte for port #FE
LD C,L ;(4) ; C = medium part of tone period
DEC DE ;(6) ; decrement cycle count
JP (IX) ;(8) ; do another cycle
;; BE-AGAIN ; halfway through cycle
L03F2: LD C,L ;(4) ; C = medium part of tone period
INC C ;(4) ; adds 16 cycles to make duration of high = duration of low
JP (IX) ;(8) ; do high pulse of tone
;; BE-END
L03F6: EI ; Enable Interrupts
RET ;
; ------------------
; THE 'BEEP' COMMAND
; ------------------
; BASIC interface to BEEPER subroutine.
; Invoked in BASIC with:
; BEEP dur, pitch
; where dur = duration in seconds
; pitch = # of semitones above/below middle C
;
; Enter with: pitch on top of calculator stack
; duration next on calculator stack
;
;; beep
L03F8: RST 28H ;; FP-CALC
DEFB $31 ;;duplicate ; duplicate pitch
DEFB $27 ;;int ; convert to integer
DEFB $C0 ;;st-mem-0 ; store integer pitch to memory 0
DEFB $03 ;;subtract ; calculate fractional part of pitch = fp_pitch - int_pitch
DEFB $34 ;;stk-data ; push constant
DEFB $EC ;;Exponent: $7C, Bytes: 4 ; constant = 0.05762265
DEFB $6C,$98,$1F,$F5 ;;($6C,$98,$1F,$F5)
DEFB $04 ;;multiply ; compute:
DEFB $A1 ;;stk-one ; 1 + 0.05762265 * fraction_part(pitch)
DEFB $0F ;;addition
DEFB $38 ;;end-calc ; leave on calc stack
LD HL,$5C92 ; MEM-0: number stored here is in 16 bit integer format (pitch)
; 0, 0/FF (pos/neg), LSB, MSB, 0
; LSB/MSB is stored in two's complement
; In the following, the pitch is checked if it is in the range -128<=p<=127
LD A,(HL) ; First byte must be zero, otherwise
AND A ; error in integer conversion
JR NZ,L046C ; to REPORT-B
INC HL ;
LD C,(HL) ; C = pos/neg flag = 0/FF
INC HL ;
LD B,(HL) ; B = LSB, two's complement
LD A,B ;
RLA ;
SBC A,A ; A = 0/FF if B is pos/neg
CP C ; must be the same as C if the pitch is -128<=p<=127
JR NZ,L046C ; if no, error REPORT-B
INC HL ; if -128<=p<=127, MSB will be 0/FF if B is pos/neg
CP (HL) ; verify this
JR NZ,L046C ; if no, error REPORT-B
; now we know -128<=p<=127
LD A,B ; A = pitch + 60
ADD A,$3C ; if -60<=pitch<=67,
JP P,L0425 ; goto BE-i-OK
JP PO,L046C ; if pitch <= 67 goto REPORT-B
; lower bound of pitch set at -60
;; BE-I-OK ; here, -60<=pitch<=127
; and A=pitch+60 -> 0<=A<=187
L0425: LD B,$FA ; 6 octaves below middle C
;; BE-OCTAVE ; A=# semitones above 5 octaves below middle C
L0427: INC B ; increment octave
SUB $0C ; 12 semitones = one octave
JR NC,L0427 ; to BE-OCTAVE
ADD A,$0C ; A = # semitones above C (0-11)
PUSH BC ; B = octave displacement from middle C, 2's complement: -5<=B<=10
LD HL,L046E ; Address: semi-tone
CALL L3406 ; routine LOC-MEM
; HL = 5*A + $046E
CALL L33B4 ; routine STACK-NUM
; read FP value (freq) from semitone table (HL) and push onto calc stack
RST 28H ;; FP-CALC
DEFB $04 ;;multiply mult freq by 1 + 0.0576 * fraction_part(pitch) stacked earlier
;; thus taking into account fractional part of pitch.
;; the number 0.0576*frequency is the distance in Hz to the next
;; note (verify with the frequencies recorded in the semitone
;; table below) so that the fraction_part of the pitch does
;; indeed represent a fractional distance to the next note.
DEFB $38 ;;end-calc HL points to first byte of fp num on stack = middle frequency to generate
POP AF ; A = octave displacement from middle C, 2's complement: -5<=A<=10
ADD A,(HL) ; increase exponent by A (equivalent to multiplying by 2^A)
LD (HL),A ;
RST 28H ;; FP-CALC
DEFB $C0 ;;st-mem-0 ; store frequency in memory 0
DEFB $02 ;;delete ; remove from calc stack
DEFB $31 ;;duplicate ; duplicate duration (seconds)
DEFB $38 ;;end-calc
CALL L1E94 ; routine FIND-INT1 ; FP duration to A
CP $0B ; if dur > 10 seconds,
JR NC,L046C ; goto REPORT-B
;;; The following calculation finds the tone period for HL and the cycle count
;;; for DE expected in the BEEPER subroutine. From the example in the BEEPER comments,
;;;
;;; HL = ((fCPU / f) - 236) / 8 = fCPU/8/f - 236/8 = 437500/f -29.5
;;; DE = duration * frequency - 1
;;;
;;; Note the different constant (30.125) used in the calculation of HL
;;; below. This is probably an error.
RST 28H ;; FP-CALC
DEFB $E0 ;;get-mem-0 ; push frequency
DEFB $04 ;;multiply ; result1: #cycles = duration * frequency
DEFB $E0 ;;get-mem-0 ; push frequency
DEFB $34 ;;stk-data ; push constant
DEFB $80 ;;Exponent $93, Bytes: 3 ; constant = 437500
DEFB $43,$55,$9F,$80 ;;($55,$9F,$80,$00)
DEFB $01 ;;exchange ; frequency on top
DEFB $05 ;;division ; 437500 / frequency
DEFB $34 ;;stk-data ; push constant
DEFB $35 ;;Exponent: $85, Bytes: 1 ; constant = 30.125
DEFB $71 ;;($71,$00,$00,$00)
DEFB $03 ;;subtract ; result2: tone_period(HL) = 437500 / freq - 30.125
DEFB $38 ;;end-calc
CALL L1E99 ; routine FIND-INT2
PUSH BC ; BC = tone_period(HL)
CALL L1E99 ; routine FIND-INT2, BC = #cycles to generate
POP HL ; HL = tone period
LD D,B ;
LD E,C ; DE = #cycles
LD A,D ;
OR E ;
RET Z ; if duration = 0, skip BEEP and avoid 65536 cycle
; boondoggle that would occur next
DEC DE ; DE = #cycles - 1
JP L03B5 ; to BEEPER
; ---
;; REPORT-B
L046C: RST 08H ; ERROR-1
DEFB $0A ; Error Report: Integer out of range
; ---------------------
; THE 'SEMI-TONE' TABLE
; ---------------------
;
; Holds frequencies corresponding to semitones in middle octave.
; To move n octaves higher or lower, frequencies are multiplied by 2^n.
;; semi-tone five byte fp decimal freq note (middle)
L046E: DEFB $89, $02, $D0, $12, $86; 261.625565290 C
DEFB $89, $0A, $97, $60, $75; 277.182631135 C#
DEFB $89, $12, $D5, $17, $1F; 293.664768100 D
DEFB $89, $1B, $90, $41, $02; 311.126983881 D#
DEFB $89, $24, $D0, $53, $CA; 329.627557039 E
DEFB $89, $2E, $9D, $36, $B1; 349.228231549 F
DEFB $89, $38, $FF, $49, $3E; 369.994422674 F#
DEFB $89, $43, $FF, $6A, $73; 391.995436072 G
DEFB $89, $4F, $A7, $00, $54; 415.304697513 G#
DEFB $89, $5C, $00, $00, $00; 440.000000000 A
DEFB $89, $69, $14, $F6, $24; 466.163761616 A#
DEFB $89, $76, $F1, $10, $05; 493.883301378 B
; "Music is the hidden mathematical endeavour of a soul unconscious it
; is calculating" - Gottfried Wilhelm Liebnitz 1646 - 1716
;****************************************
;** Part 4. CASSETTE HANDLING ROUTINES **
;****************************************
; These routines begin with the service routines followed by a single
; command entry point.
; The first of these service routines is a curiosity.
; -----------------------
; THE 'ZX81 NAME' ROUTINE
; -----------------------
; This routine fetches a filename in ZX81 format and is not used by the
; cassette handling routines in this ROM.
;; zx81-name
L04AA: CALL L24FB ; routine SCANNING to evaluate expression.
LD A,($5C3B) ; fetch system variable FLAGS.
ADD A,A ; test bit 7 - syntax, bit 6 - result type.
JP M,L1C8A ; to REPORT-C if not string result
; 'Nonsense in BASIC'.
POP HL ; drop return address.
RET NC ; return early if checking syntax.
PUSH HL ; re-save return address.
CALL L2BF1 ; routine STK-FETCH fetches string parameters.
LD H,D ; transfer start of filename
LD L,E ; to the HL register.
DEC C ; adjust to point to last character and
RET M ; return if the null string.
; or multiple of 256!
ADD HL,BC ; find last character of the filename.
; and also clear carry.
SET 7,(HL) ; invert it.
RET ; return.
; =========================================
;
; PORT 254 ($FE)
;
; spk mic { border }
; ___ ___ ___ ___ ___ ___ ___ ___
; PORT | | | | | | | | |
; 254 | | | | | | | | |
; $FE |___|___|___|___|___|___|___|___|
; 7 6 5 4 3 2 1 0
;
; ----------------------------------
; Save header and program/data bytes
; ----------------------------------
; This routine saves a section of data. It is called from SA-CTRL to save the
; seventeen bytes of header data. It is also the exit route from that routine
; when it is set up to save the actual data.
; On entry -
; HL points to start of data.
; IX points to descriptor.
; The accumulator is set to $00 for a header, $FF for data.
;; SA-BYTES
L04C2: LD HL,L053F ; address: SA/LD-RET
PUSH HL ; is pushed as common exit route.
; however there is only one non-terminal exit
; point.
LD HL,$1F80 ; a timing constant H=$1F, L=$80
; inner and outer loop counters
; a five second lead-in is used for a header.
BIT 7,A ; test one bit of accumulator.
; (AND A ?)
JR Z,L04D0 ; skip to SA-FLAG if a header is being saved.
; else is data bytes and a shorter lead-in is used.
LD HL,$0C98 ; another timing value H=$0C, L=$98.
; a two second lead-in is used for the data.
;; SA-FLAG
L04D0: EX AF,AF' ; save flag
INC DE ; increase length by one.
DEC IX ; decrease start.
DI ; disable interrupts
LD A,$02 ; select red for border, microphone bit on.
LD B,A ; also does as an initial slight counter value.
;; SA-LEADER
L04D8: DJNZ L04D8 ; self loop to SA-LEADER for delay.
; after initial loop, count is $A4 (or $A3)
OUT ($FE),A ; output byte $02/$0D to tape port.
XOR $0F ; switch from RED (mic on) to CYAN (mic off).
LD B,$A4 ; hold count. also timed instruction.
DEC L ; originally $80 or $98.
; but subsequently cycles 256 times.
JR NZ,L04D8 ; back to SA-LEADER until L is zero.
; the outer loop is counted by H
DEC B ; decrement count
DEC H ; originally twelve or thirty-one.
JP P,L04D8 ; back to SA-LEADER until H becomes $FF
; now send a sync pulse. At this stage mic is off and A holds value
; for mic on.
; A sync pulse is much shorter than the steady pulses of the lead-in.
LD B,$2F ; another short timed delay.
;; SA-SYNC-1
L04EA: DJNZ L04EA ; self loop to SA-SYNC-1
OUT ($FE),A ; switch to mic on and red.
LD A,$0D ; prepare mic off - cyan
LD B,$37 ; another short timed delay.
;; SA-SYNC-2
L04F2: DJNZ L04F2 ; self loop to SA-SYNC-2
OUT ($FE),A ; output mic off, cyan border.
LD BC,$3B0E ; B=$3B time(*), C=$0E, YELLOW, MIC OFF.
;
EX AF,AF' ; restore saved flag
; which is 1st byte to be saved.
LD L,A ; and transfer to L.
; the initial parity is A, $FF or $00.
JP L0507 ; JUMP forward to SA-START ->
; the mid entry point of loop.
; -------------------------
; During the save loop a parity byte is maintained in H.
; the save loop begins by testing if reduced length is zero and if so
; the final parity byte is saved reducing count to $FFFF.
;; SA-LOOP
L04FE: LD A,D ; fetch high byte
OR E ; test against low byte.
JR Z,L050E ; forward to SA-PARITY if zero.
LD L,(IX+$00) ; load currently addressed byte to L.
;; SA-LOOP-P
L0505: LD A,H ; fetch parity byte.
XOR L ; exclusive or with new byte.
; -> the mid entry point of loop.
;; SA-START
L0507: LD H,A ; put parity byte in H.
LD A,$01 ; prepare blue, mic=on.
SCF ; set carry flag ready to rotate in.
JP L0525 ; JUMP forward to SA-8-BITS -8->
; ---
;; SA-PARITY
L050E: LD L,H ; transfer the running parity byte to L and
JR L0505 ; back to SA-LOOP-P
; to output that byte before quitting normally.
; ---
; The entry point to save yellow part of bit.
; A bit consists of a period with mic on and blue border followed by
; a period of mic off with yellow border.
; Note. since the DJNZ instruction does not affect flags, the zero flag is
; used to indicate which of the two passes is in effect and the carry
; maintains the state of the bit to be saved.
;; SA-BIT-2
L0511: LD A,C ; fetch 'mic on and yellow' which is
; held permanently in C.
BIT 7,B ; set the zero flag. B holds $3E.
; The entry point to save 1 entire bit. For first bit B holds $3B(*).
; Carry is set if saved bit is 1. zero is reset NZ on entry.
;; SA-BIT-1
L0514: DJNZ L0514 ; self loop for delay to SA-BIT-1
JR NC,L051C ; forward to SA-OUT if bit is 0.
; but if bit is 1 then the mic state is held for longer.
LD B,$42 ; set timed delay. (66 decimal)
;; SA-SET
L051A: DJNZ L051A ; self loop to SA-SET
; (roughly an extra 66*13 clock cycles)
;; SA-OUT
L051C: OUT ($FE),A ; blue and mic on OR yellow and mic off.
LD B,$3E ; set up delay
JR NZ,L0511 ; back to SA-BIT-2 if zero reset NZ (first pass)
; proceed when the blue and yellow bands have been output.
DEC B ; change value $3E to $3D.
XOR A ; clear carry flag (ready to rotate in).
INC A ; reset zero flag i.e. NZ.
; -8->
;; SA-8-BITS
L0525: RL L ; rotate left through carry
; C<76543210<C
JP NZ,L0514 ; JUMP back to SA-BIT-1
; until all 8 bits done.
; when the initial set carry is passed out again then a byte is complete.
DEC DE ; decrease length
INC IX ; increase byte pointer
LD B,$31 ; set up timing.
LD A,$7F ; test the space key and
IN A,($FE) ; return to common exit (to restore border)
RRA ; if a space is pressed
RET NC ; return to SA/LD-RET. - - >
; now test if byte counter has reached $FFFF.
LD A,D ; fetch high byte
INC A ; increment.
JP NZ,L04FE ; JUMP to SA-LOOP if more bytes.
LD B,$3B ; a final delay.
;; SA-DELAY
L053C: DJNZ L053C ; self loop to SA-DELAY
RET ; return - - >
; ------------------------------
; THE 'SAVE/LOAD RETURN' ROUTINE
; ------------------------------
; The address of this routine is pushed on the stack prior to any load/save
; operation and it handles normal completion with the restoration of the
; border and also abnormal termination when the break key, or to be more
; precise the space key is pressed during a tape operation.
;
; - - >
;; SA/LD-RET
L053F: PUSH AF ; preserve accumulator throughout.
LD A,($5C48) ; fetch border colour from BORDCR.
AND $38 ; mask off paper bits.
RRCA ; rotate
RRCA ; to the
RRCA ; range 0-7.
OUT ($FE),A ; change the border colour.
LD A,$7F ; read from port address $7FFE the
IN A,($FE) ; row with the space key at outside.
RRA ; test for space key pressed.
EI ; enable interrupts
JR C,L0554 ; forward to SA/LD-END if not
;; REPORT-Da
L0552: RST 08H ; ERROR-1
DEFB $0C ; Error Report: BREAK - CONT repeats
; ---
;; SA/LD-END
L0554: POP AF ; restore the accumulator.
RET ; return.
; ------------------------------------
; Load header or block of information
; ------------------------------------
; This routine is used to load bytes and on entry A is set to $00 for a
; header or to $FF for data. IX points to the start of receiving location
; and DE holds the length of bytes to be loaded. If, on entry the carry flag
; is set then data is loaded, if reset then it is verified.
;; LD-BYTES
L0556: INC D ; reset the zero flag without disturbing carry.
EX AF,AF' ; preserve entry flags.
DEC D ; restore high byte of length.
DI ; disable interrupts
LD A,$0F ; make the border white and mic off.
OUT ($FE),A ; output to port.
LD HL,L053F ; Address: SA/LD-RET
PUSH HL ; is saved on stack as terminating routine.
; the reading of the EAR bit (D6) will always be preceded by a test of the
; space key (D0), so store the initial post-test state.
IN A,($FE) ; read the ear state - bit 6.
RRA ; rotate to bit 5.
AND $20 ; isolate this bit.
OR $02 ; combine with red border colour.
LD C,A ; and store initial state long-term in C.
CP A ; set the zero flag.
;
;; LD-BREAK
L056B: RET NZ ; return if at any time space is pressed.
;; LD-START
L056C: CALL L05E7 ; routine LD-EDGE-1
JR NC,L056B ; back to LD-BREAK with time out and no
; edge present on tape.
; but continue when a transition is found on tape.
LD HL,$0415 ; set up 16-bit outer loop counter for
; approx 1 second delay.
;; LD-WAIT
L0574: DJNZ L0574 ; self loop to LD-WAIT (for 256 times)
DEC HL ; decrease outer loop counter.
LD A,H ; test for
OR L ; zero.
JR NZ,L0574 ; back to LD-WAIT, if not zero, with zero in B.
; continue after delay with H holding zero and B also.
; sample 256 edges to check that we are in the middle of a lead-in section.
CALL L05E3 ; routine LD-EDGE-2
JR NC,L056B ; back to LD-BREAK
; if no edges at all.
;; LD-LEADER
L0580: LD B,$9C ; set timing value.
CALL L05E3 ; routine LD-EDGE-2
JR NC,L056B ; back to LD-BREAK if time-out
LD A,$C6 ; two edges must be spaced apart.
CP B ; compare
JR NC,L056C ; back to LD-START if too close together for a
; lead-in.
INC H ; proceed to test 256 edged sample.
JR NZ,L0580 ; back to LD-LEADER while more to do.
; sample indicates we are in the middle of a two or five second lead-in.
; Now test every edge looking for the terminal sync signal.
;; LD-SYNC
L058F: LD B,$C9 ; initial timing value in B.
CALL L05E7 ; routine LD-EDGE-1
JR NC,L056B ; back to LD-BREAK with time-out.
LD A,B ; fetch augmented timing value from B.
CP $D4 ; compare
JR NC,L058F ; back to LD-SYNC if gap too big, that is,
; a normal lead-in edge gap.
; but a short gap will be the sync pulse.
; in which case another edge should appear before B rises to $FF
CALL L05E7 ; routine LD-EDGE-1
RET NC ; return with time-out.
; proceed when the sync at the end of the lead-in is found.
; We are about to load data so change the border colours.
LD A,C ; fetch long-term mask from C
XOR $03 ; and make blue/yellow.
LD C,A ; store the new long-term byte.
LD H,$00 ; set up parity byte as zero.
LD B,$B0 ; timing.
JR L05C8 ; forward to LD-MARKER
; the loop mid entry point with the alternate
; zero flag reset to indicate first byte
; is discarded.
; --------------
; the loading loop loads each byte and is entered at the mid point.
;; LD-LOOP
L05A9: EX AF,AF' ; restore entry flags and type in A.
JR NZ,L05B3 ; forward to LD-FLAG if awaiting initial flag
; which is to be discarded.
JR NC,L05BD ; forward to LD-VERIFY if not to be loaded.
LD (IX+$00),L ; place loaded byte at memory location.
JR L05C2 ; forward to LD-NEXT
; ---
;; LD-FLAG
L05B3: RL C ; preserve carry (verify) flag in long-term
; state byte. Bit 7 can be lost.
XOR L ; compare type in A with first byte in L.
RET NZ ; return if no match e.g. CODE vs. DATA.
; continue when data type matches.
LD A,C ; fetch byte with stored carry
RRA ; rotate it to carry flag again
LD C,A ; restore long-term port state.
INC DE ; increment length ??
JR L05C4 ; forward to LD-DEC.
; but why not to location after ?
; ---
; for verification the byte read from tape is compared with that in memory.
;; LD-VERIFY
L05BD: LD A,(IX+$00) ; fetch byte from memory.
XOR L ; compare with that on tape
RET NZ ; return if not zero.
;; LD-NEXT
L05C2: INC IX ; increment byte pointer.
;; LD-DEC
L05C4: DEC DE ; decrement length.
EX AF,AF' ; store the flags.
LD B,$B2 ; timing.
; when starting to read 8 bits the receiving byte is marked with bit at right.
; when this is rotated out again then 8 bits have been read.
;; LD-MARKER
L05C8: LD L,$01 ; initialize as %00000001
;; LD-8-BITS
L05CA: CALL L05E3 ; routine LD-EDGE-2 increments B relative to
; gap between 2 edges.
RET NC ; return with time-out.
LD A,$CB ; the comparison byte.
CP B ; compare to incremented value of B.
; if B is higher then bit on tape was set.
; if <= then bit on tape is reset.
RL L ; rotate the carry bit into L.
LD B,$B0 ; reset the B timer byte.
JP NC,L05CA ; JUMP back to LD-8-BITS
; when carry set then marker bit has been passed out and byte is complete.
LD A,H ; fetch the running parity byte.
XOR L ; include the new byte.
LD H,A ; and store back in parity register.
LD A,D ; check length of
OR E ; expected bytes.
JR NZ,L05A9 ; back to LD-LOOP
; while there are more.
; when all bytes loaded then parity byte should be zero.
LD A,H ; fetch parity byte.
CP $01 ; set carry if zero.
RET ; return
; in no carry then error as checksum disagrees.
; -------------------------
; Check signal being loaded
; -------------------------
; An edge is a transition from one mic state to another.
; More specifically a change in bit 6 of value input from port $FE.
; Graphically it is a change of border colour, say, blue to yellow.
; The first entry point looks for two adjacent edges. The second entry point
; is used to find a single edge.
; The B register holds a count, up to 256, within which the edge (or edges)
; must be found. The gap between two edges will be more for a '1' than a '0'
; so the value of B denotes the state of the bit (two edges) read from tape.
; ->
;; LD-EDGE-2
L05E3: CALL L05E7 ; call routine LD-EDGE-1 below.
RET NC ; return if space pressed or time-out.
; else continue and look for another adjacent
; edge which together represent a bit on the
; tape.
; ->
; this entry point is used to find a single edge from above but also
; when detecting a read-in signal on the tape.
;; LD-EDGE-1
L05E7: LD A,$16 ; a delay value of twenty two.
;; LD-DELAY
L05E9: DEC A ; decrement counter
JR NZ,L05E9 ; loop back to LD-DELAY 22 times.
AND A ; clear carry.
;; LD-SAMPLE
L05ED: INC B ; increment the time-out counter.
RET Z ; return with failure when $FF passed.
LD A,$7F ; prepare to read keyboard and EAR port
IN A,($FE) ; row $7FFE. bit 6 is EAR, bit 0 is SPACE key.
RRA ; test outer key the space. (bit 6 moves to 5)
RET NC ; return if space pressed. >>>
XOR C ; compare with initial long-term state.
AND $20 ; isolate bit 5
JR Z,L05ED ; back to LD-SAMPLE if no edge.
; but an edge, a transition of the EAR bit, has been found so switch the
; long-term comparison byte containing both border colour and EAR bit.
LD A,C ; fetch comparison value.
CPL ; switch the bits
LD C,A ; and put back in C for long-term.
AND $07 ; isolate new colour bits.
OR $08 ; set bit 3 - MIC off.
OUT ($FE),A ; send to port to effect the change of colour.
SCF ; set carry flag signaling edge found within
; time allowed.
RET ; return.
; ---------------------------------
; Entry point for all tape commands
; ---------------------------------
; This is the single entry point for the four tape commands.
; The routine first determines in what context it has been called by examining
; the low byte of the Syntax table entry which was stored in T_ADDR.
; Subtracting $EO (the present arrangement) gives a value of
; $00 - SAVE
; $01 - LOAD
; $02 - VERIFY
; $03 - MERGE
; As with all commands the address STMT-RET is on the stack.
;; SAVE-ETC
L0605: POP AF ; discard address STMT-RET.
LD A,($5C74) ; fetch T_ADDR
; Now reduce the low byte of the Syntax table entry to give command.
; Note. For ZASM use SUB $E0 as next instruction.
L0609: SUB L1ADF + 1 % 256 ; subtract the known offset.
; ( is SUB $E0 in standard ROM )
LD ($5C74),A ; and put back in T_ADDR as 0,1,2, or 3
; for future reference.
CALL L1C8C ; routine EXPT-EXP checks that a string
; expression follows and stacks the
; parameters in run-time.
CALL L2530 ; routine SYNTAX-Z
JR Z,L0652 ; forward to SA-DATA if checking syntax.
LD BC,$0011 ; presume seventeen bytes for a header.
LD A,($5C74) ; fetch command from T_ADDR.
AND A ; test for zero - SAVE.
JR Z,L0621 ; forward to SA-SPACE if so.
LD C,$22 ; else double length to thirty four.
;; SA-SPACE
L0621: RST 30H ; BC-SPACES creates 17/34 bytes in workspace.
PUSH DE ; transfer the start of new space to
POP IX ; the available index register.
; ten spaces are required for the default filename but it is simpler to
; overwrite the first file-type indicator byte as well.
LD B,$0B ; set counter to eleven.
LD A,$20 ; prepare a space.
;; SA-BLANK
L0629: LD (DE),A ; set workspace location to space.
INC DE ; next location.
DJNZ L0629 ; loop back to SA-BLANK till all eleven done.
LD (IX+$01),$FF ; set first byte of ten character filename
; to $FF as a default to signal null string.
CALL L2BF1 ; routine STK-FETCH fetches the filename
; parameters from the calculator stack.
; length of string in BC.
; start of string in DE.
LD HL,$FFF6 ; prepare the value minus ten.
DEC BC ; decrement length.
; ten becomes nine, zero becomes $FFFF.
ADD HL,BC ; trial addition.
INC BC ; restore true length.
JR NC,L064B ; forward to SA-NAME if length is one to ten.
; the filename is more than ten characters in length or the null string.
LD A,($5C74) ; fetch command from T_ADDR.
AND A ; test for zero - SAVE.
JR NZ,L0644 ; forward to SA-NULL if not the SAVE command.
; but no more than ten characters are allowed for SAVE.
; The first ten characters of any other command parameter are acceptable.
; Weird, but necessary, if saving to sectors.
; Note. the golden rule that there are no restriction on anything is broken.
;; REPORT-Fa
L0642: RST 08H ; ERROR-1
DEFB $0E ; Error Report: Invalid file name
; continue with LOAD, MERGE, VERIFY and also SAVE within ten character limit.
;; SA-NULL
L0644: LD A,B ; test length of filename
OR C ; for zero.
JR Z,L0652 ; forward to SA-DATA if so using the 255
; indicator followed by spaces.
LD BC,$000A ; else trim length to ten.
; other paths rejoin here with BC holding length in range 1 - 10.
;; SA-NAME
L064B: PUSH IX ; push start of file descriptor.
POP HL ; and pop into HL.
INC HL ; HL now addresses first byte of filename.
EX DE,HL ; transfer destination address to DE, start
; of string in command to HL.
LDIR ; copy up to ten bytes
; if less than ten then trailing spaces follow.
; the case for the null string rejoins here.
;; SA-DATA
L0652: RST 18H ; GET-CHAR
CP $E4 ; is character after filename the token 'DATA' ?
JR NZ,L06A0 ; forward to SA-SCR$ to consider SCREEN$ if
; not.
; continue to consider DATA.
LD A,($5C74) ; fetch command from T_ADDR
CP $03 ; is it 'VERIFY' ?
JP Z,L1C8A ; jump forward to REPORT-C if so.
; 'Nonsense in BASIC'
; VERIFY "d" DATA is not allowed.
; continue with SAVE, LOAD, MERGE of DATA.
RST 20H ; NEXT-CHAR
CALL L28B2 ; routine LOOK-VARS searches variables area
; returning with carry reset if found or
; checking syntax.
SET 7,C ; this converts a simple string to a
; string array. The test for an array or string
; comes later.
JR NC,L0672 ; forward to SA-V-OLD if variable found.
LD HL,$0000 ; set destination to zero as not fixed.
LD A,($5C74) ; fetch command from T_ADDR
DEC A ; test for 1 - LOAD
JR Z,L0685 ; forward to SA-V-NEW with LOAD DATA.
; to load a new array.
; otherwise the variable was not found in run-time with SAVE/MERGE.
;; REPORT-2a
L0670: RST 08H ; ERROR-1
DEFB $01 ; Error Report: Variable not found
; continue with SAVE/LOAD DATA
;; SA-V-OLD
L0672: JP NZ,L1C8A ; to REPORT-C if not an array variable.
; or erroneously a simple string.
; 'Nonsense in BASIC'
CALL L2530 ; routine SYNTAX-Z
JR Z,L0692 ; forward to SA-DATA-1 if checking syntax.
INC HL ; step past single character variable name.
LD A,(HL) ; fetch low byte of length.
LD (IX+$0B),A ; place in descriptor.
INC HL ; point to high byte.
LD A,(HL) ; and transfer that
LD (IX+$0C),A ; to descriptor.
INC HL ; increase pointer within variable.
;; SA-V-NEW
L0685: LD (IX+$0E),C ; place character array name in header.
LD A,$01 ; default to type numeric.
BIT 6,C ; test result from look-vars.
JR Z,L068F ; forward to SA-V-TYPE if numeric.
INC A ; set type to 2 - string array.
;; SA-V-TYPE
L068F: LD (IX+$00),A ; place type 0, 1 or 2 in descriptor.
;; SA-DATA-1
L0692: EX DE,HL ; save var pointer in DE
RST 20H ; NEXT-CHAR
CP $29 ; is character ')' ?
JR NZ,L0672 ; back if not to SA-V-OLD to report
; 'Nonsense in BASIC'
RST 20H ; NEXT-CHAR advances character address.
CALL L1BEE ; routine CHECK-END errors if not end of
; the statement.
EX DE,HL ; bring back variables data pointer.
JP L075A ; jump forward to SA-ALL
; ---
; the branch was here to consider a 'SCREEN$', the display file.
;; SA-SCR$
L06A0: CP $AA ; is character the token 'SCREEN$' ?
JR NZ,L06C3 ; forward to SA-CODE if not.
LD A,($5C74) ; fetch command from T_ADDR
CP $03 ; is it MERGE ?
JP Z,L1C8A ; jump to REPORT-C if so.
; 'Nonsense in BASIC'
; continue with SAVE/LOAD/VERIFY SCREEN$.
RST 20H ; NEXT-CHAR
CALL L1BEE ; routine CHECK-END errors if not at end of
; statement.
; continue in runtime.
LD (IX+$0B),$00 ; set descriptor length
LD (IX+$0C),$1B ; to $1b00 to include bitmaps and attributes.
LD HL,$4000 ; set start to display file start.
LD (IX+$0D),L ; place start in
LD (IX+$0E),H ; the descriptor.
JR L0710 ; forward to SA-TYPE-3
; ---
; the branch was here to consider CODE.
;; SA-CODE
L06C3: CP $AF ; is character the token 'CODE' ?
JR NZ,L0716 ; forward if not to SA-LINE to consider an
; auto-started BASIC program.
LD A,($5C74) ; fetch command from T_ADDR
CP $03 ; is it MERGE ?
JP Z,L1C8A ; jump forward to REPORT-C if so.
; 'Nonsense in BASIC'
RST 20H ; NEXT-CHAR advances character address.
CALL L2048 ; routine PR-ST-END checks if a carriage
; return or ':' follows.
JR NZ,L06E1 ; forward to SA-CODE-1 if there are parameters.
LD A,($5C74) ; else fetch the command from T_ADDR.
AND A ; test for zero - SAVE without a specification.
JP Z,L1C8A ; jump to REPORT-C if so.
; 'Nonsense in BASIC'
; for LOAD/VERIFY put zero on stack to signify handle at location saved from.
CALL L1CE6 ; routine USE-ZERO
JR L06F0 ; forward to SA-CODE-2
; ---
; if there are more characters after CODE expect start and possibly length.
;; SA-CODE-1
L06E1: CALL L1C82 ; routine EXPT-1NUM checks for numeric
; expression and stacks it in run-time.
RST 18H ; GET-CHAR
CP $2C ; does a comma follow ?
JR Z,L06F5 ; forward if so to SA-CODE-3
; else allow saved code to be loaded to a specified address.
LD A,($5C74) ; fetch command from T_ADDR.
AND A ; is the command SAVE which requires length ?
JP Z,L1C8A ; jump to REPORT-C if so.
; 'Nonsense in BASIC'
; the command LOAD code may rejoin here with zero stacked as start.
;; SA-CODE-2
L06F0: CALL L1CE6 ; routine USE-ZERO stacks zero for length.
JR L06F9 ; forward to SA-CODE-4
; ---
; the branch was here with SAVE CODE start,
;; SA-CODE-3
L06F5: RST 20H ; NEXT-CHAR advances character address.
CALL L1C82 ; routine EXPT-1NUM checks for expression
; and stacks in run-time.
; paths converge here and nothing must follow.
;; SA-CODE-4
L06F9: CALL L1BEE ; routine CHECK-END errors with extraneous
; characters and quits if checking syntax.
; in run-time there are two 16-bit parameters on the calculator stack.
CALL L1E99 ; routine FIND-INT2 gets length.
LD (IX+$0B),C ; place length
LD (IX+$0C),B ; in descriptor.
CALL L1E99 ; routine FIND-INT2 gets start.
LD (IX+$0D),C ; place start
LD (IX+$0E),B ; in descriptor.
LD H,B ; transfer the
LD L,C ; start to HL also.
;; SA-TYPE-3
L0710: LD (IX+$00),$03 ; place type 3 - code in descriptor.
JR L075A ; forward to SA-ALL.
; ---
; the branch was here with BASIC to consider an optional auto-start line
; number.
;; SA-LINE
L0716: CP $CA ; is character the token 'LINE' ?
JR Z,L0723 ; forward to SA-LINE-1 if so.
; else all possibilities have been considered and nothing must follow.
CALL L1BEE ; routine CHECK-END
; continue in run-time to save BASIC without auto-start.
LD (IX+$0E),$80 ; place high line number in descriptor to
; disable auto-start.
JR L073A ; forward to SA-TYPE-0 to save program.
; ---
; the branch was here to consider auto-start.
;; SA-LINE-1
L0723: LD A,($5C74) ; fetch command from T_ADDR
AND A ; test for SAVE.
JP NZ,L1C8A ; jump forward to REPORT-C with anything else.
; 'Nonsense in BASIC'
;
RST 20H ; NEXT-CHAR
CALL L1C82 ; routine EXPT-1NUM checks for numeric
; expression and stacks in run-time.
CALL L1BEE ; routine CHECK-END quits if syntax path.
CALL L1E99 ; routine FIND-INT2 fetches the numeric
; expression.
LD (IX+$0D),C ; place the auto-start
LD (IX+$0E),B ; line number in the descriptor.
; Note. this isn't checked, but is subsequently handled by the system.
; If the user typed 40000 instead of 4000 then it won't auto-start
; at line 4000, or indeed, at all.
; continue to save program and any variables.
;; SA-TYPE-0
L073A: LD (IX+$00),$00 ; place type zero - program in descriptor.
LD HL,($5C59) ; fetch E_LINE to HL.
LD DE,($5C53) ; fetch PROG to DE.
SCF ; set carry flag to calculate from end of
; variables E_LINE -1.
SBC HL,DE ; subtract to give total length.
LD (IX+$0B),L ; place total length
LD (IX+$0C),H ; in descriptor.
LD HL,($5C4B) ; load HL from system variable VARS
SBC HL,DE ; subtract to give program length.
LD (IX+$0F),L ; place length of program
LD (IX+$10),H ; in the descriptor.
EX DE,HL ; start to HL, length to DE.
;; SA-ALL
L075A: LD A,($5C74) ; fetch command from T_ADDR
AND A ; test for zero - SAVE.
JP Z,L0970 ; jump forward to SA-CONTRL with SAVE ->
; ---
; continue with LOAD, MERGE and VERIFY.
PUSH HL ; save start.
LD BC,$0011 ; prepare to add seventeen
ADD IX,BC ; to point IX at second descriptor.
;; LD-LOOK-H
L0767: PUSH IX ; save IX
LD DE,$0011 ; seventeen bytes
XOR A ; reset zero flag
SCF ; set carry flag
CALL L0556 ; routine LD-BYTES loads a header from tape
; to second descriptor.
POP IX ; restore IX.
JR NC,L0767 ; loop back to LD-LOOK-H until header found.
LD A,$FE ; select system channel 'S'
CALL L1601 ; routine CHAN-OPEN opens it.
LD (IY+$52),$03 ; set SCR_CT to 3 lines.
LD C,$80 ; C has bit 7 set to indicate type mismatch as
; a default startpoint.
LD A,(IX+$00) ; fetch loaded header type to A
CP (IX-$11) ; compare with expected type.
JR NZ,L078A ; forward to LD-TYPE with mis-match.
LD C,$F6 ; set C to minus ten - will count characters
; up to zero.
;; LD-TYPE
L078A: CP $04 ; check if type in acceptable range 0 - 3.
JR NC,L0767 ; back to LD-LOOK-H with 4 and over.
; else A indicates type 0-3.
LD DE,L09C0 ; address base of last 4 tape messages
PUSH BC ; save BC
CALL L0C0A ; routine PO-MSG outputs relevant message.
; Note. all messages have a leading newline.
POP BC ; restore BC
PUSH IX ; transfer IX,
POP DE ; the 2nd descriptor, to DE.
LD HL,$FFF0 ; prepare minus seventeen.
ADD HL,DE ; add to point HL to 1st descriptor.
LD B,$0A ; the count will be ten characters for the
; filename.
LD A,(HL) ; fetch first character and test for
INC A ; value 255.
JR NZ,L07A6 ; forward to LD-NAME if not the wildcard.
; but if it is the wildcard, then add ten to C which is minus ten for a type
; match or -128 for a type mismatch. Although characters have to be counted
; bit 7 of C will not alter from state set here.
LD A,C ; transfer $F6 or $80 to A
ADD A,B ; add $0A
LD C,A ; place result, zero or -118, in C.
; At this point we have either a type mismatch, a wildcard match or ten
; characters to be counted. The characters must be shown on the screen.
;; LD-NAME
L07A6: INC DE ; address next input character
LD A,(DE) ; fetch character
CP (HL) ; compare to expected
INC HL ; address next expected character
JR NZ,L07AD ; forward to LD-CH-PR with mismatch
INC C ; increment matched character count
;; LD-CH-PR
L07AD: RST 10H ; PRINT-A prints character
DJNZ L07A6 ; loop back to LD-NAME for ten characters.
; if ten characters matched and the types previously matched then C will
; now hold zero.
BIT 7,C ; test if all matched
JR NZ,L0767 ; back to LD-LOOK-H if not
; else print a terminal carriage return.
LD A,$0D ; prepare carriage return.
RST 10H ; PRINT-A outputs it.
; The various control routines for LOAD, VERIFY and MERGE are executed
; during the one-second gap following the header on tape.
POP HL ; restore xx
LD A,(IX+$00) ; fetch incoming type
CP $03 ; compare with CODE
JR Z,L07CB ; forward to VR-CONTRL if it is CODE.
; type is a program or an array.
LD A,($5C74) ; fetch command from T_ADDR
DEC A ; was it LOAD ?
JP Z,L0808 ; JUMP forward to LD-CONTRL if so to
; load BASIC or variables.
CP $02 ; was command MERGE ?
JP Z,L08B6 ; jump forward to ME-CONTRL if so.
; else continue into VERIFY control routine to verify.
; ----------------------------
; THE 'VERIFY CONTROL' ROUTINE
; ----------------------------
; There are two branches to this routine.
; 1) From above to verify a program or array
; 2) from earlier with no carry to load or verify code.
;; VR-CONTRL
L07CB: PUSH HL ; save pointer to data.
LD L,(IX-$06) ; fetch length of old data
LD H,(IX-$05) ; to HL.
LD E,(IX+$0B) ; fetch length of new data
LD D,(IX+$0C) ; to DE.
LD A,H ; check length of old
OR L ; for zero.
JR Z,L07E9 ; forward to VR-CONT-1 if length unspecified
; e.g. LOAD "x" CODE
; as opposed to, say, LOAD 'x' CODE 32768,300.
SBC HL,DE ; subtract the two lengths.
JR C,L0806 ; forward to REPORT-R if the length on tape is
; larger than that specified in command.
; 'Tape loading error'
JR Z,L07E9 ; forward to VR-CONT-1 if lengths match.
; a length on tape shorter than expected is not allowed for CODE
LD A,(IX+$00) ; else fetch type from tape.
CP $03 ; is it CODE ?
JR NZ,L0806 ; forward to REPORT-R if so
; 'Tape loading error'
;; VR-CONT-1
L07E9: POP HL ; pop pointer to data
LD A,H ; test for zero
OR L ; e.g. LOAD 'x' CODE
JR NZ,L07F4 ; forward to VR-CONT-2 if destination specified.
LD L,(IX+$0D) ; else use the destination in the header
LD H,(IX+$0E) ; and load code at address saved from.
;; VR-CONT-2
L07F4: PUSH HL ; push pointer to start of data block.
POP IX ; transfer to IX.
LD A,($5C74) ; fetch reduced command from T_ADDR
CP $02 ; is it VERIFY ?
SCF ; prepare a set carry flag
JR NZ,L0800 ; skip to VR-CONT-3 if not
AND A ; clear carry flag for VERIFY so that
; data is not loaded.
;; VR-CONT-3
L0800: LD A,$FF ; signal data block to be loaded
; -----------------
; Load a data block
; -----------------
; This routine is called from 3 places other than above to load a data block.
; In all cases the accumulator is first set to $FF so the routine could be
; called at the previous instruction.
;; LD-BLOCK
L0802: CALL L0556 ; routine LD-BYTES
RET C ; return if successful.
;; REPORT-R
L0806: RST 08H ; ERROR-1
DEFB $1A ; Error Report: Tape loading error
; --------------------------
; THE 'LOAD CONTROL' ROUTINE
; --------------------------
; This branch is taken when the command is LOAD with type 0, 1 or 2.
;; LD-CONTRL
L0808: LD E,(IX+$0B) ; fetch length of found data block
LD D,(IX+$0C) ; from 2nd descriptor.
PUSH HL ; save destination
LD A,H ; test for zero
OR L ;
JR NZ,L0819 ; forward if not to LD-CONT-1
INC DE ; increase length
INC DE ; for letter name
INC DE ; and 16-bit length
EX DE,HL ; length to HL,
JR L0825 ; forward to LD-CONT-2
; ---
;; LD-CONT-1
L0819: LD L,(IX-$06) ; fetch length from
LD H,(IX-$05) ; the first header.
EX DE,HL ;
SCF ; set carry flag
SBC HL,DE ;
JR C,L082E ; to LD-DATA
;; LD-CONT-2
L0825: LD DE,$0005 ; allow overhead of five bytes.
ADD HL,DE ; add in the difference in data lengths.
LD B,H ; transfer to
LD C,L ; the BC register pair
CALL L1F05 ; routine TEST-ROOM fails if not enough room.
;; LD-DATA
L082E: POP HL ; pop destination
LD A,(IX+$00) ; fetch type 0, 1 or 2.
AND A ; test for program and variables.
JR Z,L0873 ; forward if so to LD-PROG
; the type is a numeric or string array.
LD A,H ; test the destination for zero
OR L ; indicating variable does not already exist.
JR Z,L084C ; forward if so to LD-DATA-1
; else the destination is the first dimension within the array structure
DEC HL ; address high byte of total length
LD B,(HL) ; transfer to B.
DEC HL ; address low byte of total length.
LD C,(HL) ; transfer to C.
DEC HL ; point to letter of variable.
INC BC ; adjust length to
INC BC ; include these
INC BC ; three bytes also.
LD ($5C5F),IX ; save header pointer in X_PTR.
CALL L19E8 ; routine RECLAIM-2 reclaims the old variable
; sliding workspace including the two headers
; downwards.
LD IX,($5C5F) ; reload IX from X_PTR which will have been
; adjusted down by POINTERS routine.
;; LD-DATA-1
L084C: LD HL,($5C59) ; address E_LINE
DEC HL ; now point to the $80 variables end-marker.
LD C,(IX+$0B) ; fetch new data length
LD B,(IX+$0C) ; from 2nd header.
PUSH BC ; * save it.
INC BC ; adjust the
INC BC ; length to include
INC BC ; letter name and total length.
LD A,(IX-$03) ; fetch letter name from old header.
PUSH AF ; preserve accumulator though not corrupted.
CALL L1655 ; routine MAKE-ROOM creates space for variable
; sliding workspace up. IX no longer addresses
; anywhere meaningful.
INC HL ; point to first new location.
POP AF ; fetch back the letter name.
LD (HL),A ; place in first new location.
POP DE ; * pop the data length.
INC HL ; address 2nd location
LD (HL),E ; store low byte of length.
INC HL ; address next.
LD (HL),D ; store high byte.
INC HL ; address start of data.
PUSH HL ; transfer address
POP IX ; to IX register pair.
SCF ; set carry flag indicating load not verify.
LD A,$FF ; signal data not header.
JP L0802 ; JUMP back to LD-BLOCK
; -----------------
; the branch is here when a program as opposed to an array is to be loaded.
;; LD-PROG
L0873: EX DE,HL ; transfer dest to DE.
LD HL,($5C59) ; address E_LINE
DEC HL ; now variables end-marker.
LD ($5C5F),IX ; place the IX header pointer in X_PTR
LD C,(IX+$0B) ; get new length
LD B,(IX+$0C) ; from 2nd header
PUSH BC ; and save it.
CALL L19E5 ; routine RECLAIM-1 reclaims program and vars.
; adjusting X-PTR.
POP BC ; restore new length.
PUSH HL ; * save start
PUSH BC ; ** and length.
CALL L1655 ; routine MAKE-ROOM creates the space.
LD IX,($5C5F) ; reload IX from adjusted X_PTR
INC HL ; point to start of new area.
LD C,(IX+$0F) ; fetch length of BASIC on tape
LD B,(IX+$10) ; from 2nd descriptor
ADD HL,BC ; add to address the start of variables.
LD ($5C4B),HL ; set system variable VARS
LD H,(IX+$0E) ; fetch high byte of autostart line number.
LD A,H ; transfer to A
AND $C0 ; test if greater than $3F.
JR NZ,L08AD ; forward to LD-PROG-1 if so with no autostart.
LD L,(IX+$0D) ; else fetch the low byte.
LD ($5C42),HL ; set system variable to line number NEWPPC
LD (IY+$0A),$00 ; set statement NSPPC to zero.
;; LD-PROG-1
L08AD: POP DE ; ** pop the length
POP IX ; * and start.
SCF ; set carry flag
LD A,$FF ; signal data as opposed to a header.
JP L0802 ; jump back to LD-BLOCK
; ---------------------------
; THE 'MERGE CONTROL' ROUTINE
; ---------------------------
; the branch was here to merge a program and its variables or an array.
;
;; ME-CONTRL
L08B6: LD C,(IX+$0B) ; fetch length
LD B,(IX+$0C) ; of data block on tape.
PUSH BC ; save it.
INC BC ; one for the pot.
RST 30H ; BC-SPACES creates room in workspace.
; HL addresses last new location.
LD (HL),$80 ; place end-marker at end.
EX DE,HL ; transfer first location to HL.
POP DE ; restore length to DE.
PUSH HL ; save start.
PUSH HL ; and transfer it
POP IX ; to IX register.
SCF ; set carry flag to load data on tape.
LD A,$FF ; signal data not a header.
CALL L0802 ; routine LD-BLOCK loads to workspace.
POP HL ; restore first location in workspace to HL.
X08CE LD DE,($5C53) ; set DE from system variable PROG.
; now enter a loop to merge the data block in workspace with the program and
; variables.
;; ME-NEW-LP
L08D2: LD A,(HL) ; fetch next byte from workspace.
AND $C0 ; compare with $3F.
JR NZ,L08F0 ; forward to ME-VAR-LP if a variable or
; end-marker.
; continue when HL addresses a BASIC line number.
;; ME-OLD-LP
L08D7: LD A,(DE) ; fetch high byte from program area.
INC DE ; bump prog address.
CP (HL) ; compare with that in workspace.
INC HL ; bump workspace address.
JR NZ,L08DF ; forward to ME-OLD-L1 if high bytes don't match
LD A,(DE) ; fetch the low byte of program line number.
CP (HL) ; compare with that in workspace.
;; ME-OLD-L1
L08DF: DEC DE ; point to start of
DEC HL ; respective lines again.
JR NC,L08EB ; forward to ME-NEW-L2 if line number in
; workspace is less than or equal to current
; program line as has to be added to program.
PUSH HL ; else save workspace pointer.
EX DE,HL ; transfer prog pointer to HL
CALL L19B8 ; routine NEXT-ONE finds next line in DE.
POP HL ; restore workspace pointer
JR L08D7 ; back to ME-OLD-LP until destination position
; in program area found.
; ---
; the branch was here with an insertion or replacement point.
;; ME-NEW-L2
L08EB: CALL L092C ; routine ME-ENTER enters the line
JR L08D2 ; loop back to ME-NEW-LP.
; ---
; the branch was here when the location in workspace held a variable.
;; ME-VAR-LP
L08F0: LD A,(HL) ; fetch first byte of workspace variable.
LD C,A ; copy to C also.
CP $80 ; is it the end-marker ?
RET Z ; return if so as complete. >>>>>
PUSH HL ; save workspace area pointer.
LD HL,($5C4B) ; load HL with VARS - start of variables area.
;; ME-OLD-VP
L08F9: LD A,(HL) ; fetch first byte.
CP $80 ; is it the end-marker ?
JR Z,L0923 ; forward if so to ME-VAR-L2 to add
; variable at end of variables area.
CP C ; compare with variable in workspace area.
JR Z,L0909 ; forward to ME-OLD-V2 if a match to replace.
; else entire variables area has to be searched.
;; ME-OLD-V1
L0901: PUSH BC ; save character in C.
CALL L19B8 ; routine NEXT-ONE gets following variable
; address in DE.
POP BC ; restore character in C
EX DE,HL ; transfer next address to HL.
JR L08F9 ; loop back to ME-OLD-VP
; ---
; the branch was here when first characters of name matched.
;; ME-OLD-V2
L0909: AND $E0 ; keep bits 11100000
CP $A0 ; compare 10100000 - a long-named variable.
JR NZ,L0921 ; forward to ME-VAR-L1 if just one-character.
; but long-named variables have to be matched character by character.
POP DE ; fetch workspace 1st character pointer
PUSH DE ; and save it on the stack again.
PUSH HL ; save variables area pointer on stack.
;; ME-OLD-V3
L0912: INC HL ; address next character in vars area.
INC DE ; address next character in workspace area.
LD A,(DE) ; fetch workspace character.
CP (HL) ; compare to variables character.
JR NZ,L091E ; forward to ME-OLD-V4 with a mismatch.
RLA ; test if the terminal inverted character.
JR NC,L0912 ; loop back to ME-OLD-V3 if more to test.
; otherwise the long name matches in its entirety.
POP HL ; restore pointer to first character of variable
JR L0921 ; forward to ME-VAR-L1
; ---
; the branch is here when two characters don't match
;; ME-OLD-V4
L091E: POP HL ; restore the prog/vars pointer.
JR L0901 ; back to ME-OLD-V1 to resume search.
; ---
; branch here when variable is to replace an existing one
;; ME-VAR-L1
L0921: LD A,$FF ; indicate a replacement.
; this entry point is when A holds $80 indicating a new variable.
;; ME-VAR-L2
L0923: POP DE ; pop workspace pointer.
EX DE,HL ; now make HL workspace pointer, DE vars pointer
INC A ; zero flag set if replacement.
SCF ; set carry flag indicating a variable not a
; program line.
CALL L092C ; routine ME-ENTER copies variable in.
JR L08F0 ; loop back to ME-VAR-LP
; ------------------------
; Merge a Line or Variable
; ------------------------
; A BASIC line or variable is inserted at the current point. If the line
; number or variable names match (zero flag set) then a replacement takes
; place.
;; ME-ENTER
L092C: JR NZ,L093E ; forward to ME-ENT-1 for insertion only.
; but the program line or variable matches so old one is reclaimed.
EX AF,AF' ; save flag??
LD ($5C5F),HL ; preserve workspace pointer in dynamic X_PTR
EX DE,HL ; transfer program dest pointer to HL.
CALL L19B8 ; routine NEXT-ONE finds following location
; in program or variables area.
CALL L19E8 ; routine RECLAIM-2 reclaims the space between.
EX DE,HL ; transfer program dest pointer back to DE.
LD HL,($5C5F) ; fetch adjusted workspace pointer from X_PTR
EX AF,AF' ; restore flags.
; now the new line or variable is entered.
;; ME-ENT-1
L093E: EX AF,AF' ; save or re-save flags.
PUSH DE ; save dest pointer in prog/vars area.
CALL L19B8 ; routine NEXT-ONE finds next in workspace.
; gets next in DE, difference in BC.
; prev addr in HL
LD ($5C5F),HL ; store pointer in X_PTR
LD HL,($5C53) ; load HL from system variable PROG
EX (SP),HL ; swap with prog/vars pointer on stack.
PUSH BC ; ** save length of new program line/variable.
EX AF,AF' ; fetch flags back.
JR C,L0955 ; skip to ME-ENT-2 if variable
DEC HL ; address location before pointer
CALL L1655 ; routine MAKE-ROOM creates room for BASIC line
INC HL ; address next.
JR L0958 ; forward to ME-ENT-3
; ---
;; ME-ENT-2
L0955: CALL L1655 ; routine MAKE-ROOM creates room for variable.
;; ME-ENT-3
L0958: INC HL ; address next?
POP BC ; ** pop length
POP DE ; * pop value for PROG which may have been
; altered by POINTERS if first line.
LD ($5C53),DE ; set PROG to original value.
LD DE,($5C5F) ; fetch adjusted workspace pointer from X_PTR
PUSH BC ; save length
PUSH DE ; and workspace pointer
EX DE,HL ; make workspace pointer source, prog/vars
; pointer the destination
LDIR ; copy bytes of line or variable into new area.
POP HL ; restore workspace pointer.
POP BC ; restore length.
PUSH DE ; save new prog/vars pointer.
CALL L19E8 ; routine RECLAIM-2 reclaims the space used
; by the line or variable in workspace block
; as no longer required and space could be
; useful for adding more lines.
POP DE ; restore the prog/vars pointer
RET ; return.
; --------------------------
; THE 'SAVE CONTROL' ROUTINE
; --------------------------
; A branch from the main SAVE-ETC routine at SAVE-ALL.
; First the header data is saved. Then after a wait of 1 second
; the data itself is saved.
; HL points to start of data.
; IX points to start of descriptor.
;; SA-CONTRL
L0970: PUSH HL ; save start of data
LD A,$FD ; select system channel 'S'
CALL L1601 ; routine CHAN-OPEN
XOR A ; clear to address table directly
LD DE,L09A1 ; address: tape-msgs
CALL L0C0A ; routine PO-MSG -
; 'Start tape then press any key.'
SET 5,(IY+$02) ; TV_FLAG - Signal lower screen requires
; clearing
CALL L15D4 ; routine WAIT-KEY
PUSH IX ; save pointer to descriptor.
LD DE,$0011 ; there are seventeen bytes.
XOR A ; signal a header.
CALL L04C2 ; routine SA-BYTES
POP IX ; restore descriptor pointer.
LD B,$32 ; wait for a second - 50 interrupts.
;; SA-1-SEC
L0991: HALT ; wait for interrupt
DJNZ L0991 ; back to SA-1-SEC until pause complete.
LD E,(IX+$0B) ; fetch length of bytes from the
LD D,(IX+$0C) ; descriptor.
LD A,$FF ; signal data bytes.
POP IX ; retrieve pointer to start
JP L04C2 ; jump back to SA-BYTES
; Arrangement of two headers in workspace.
; Originally IX addresses first location and only one header is required
; when saving.
;
; OLD NEW PROG DATA DATA CODE
; HEADER HEADER num chr NOTES.
; ------ ------ ---- ---- ---- ---- -----------------------------
; IX-$11 IX+$00 0 1 2 3 Type.
; IX-$10 IX+$01 x x x x F ($FF if filename is null).
; IX-$0F IX+$02 x x x x i
; IX-$0E IX+$03 x x x x l
; IX-$0D IX+$04 x x x x e
; IX-$0C IX+$05 x x x x n
; IX-$0B IX+$06 x x x x a
; IX-$0A IX+$07 x x x x m
; IX-$09 IX+$08 x x x x e
; IX-$08 IX+$09 x x x x .
; IX-$07 IX+$0A x x x x (terminal spaces).
; IX-$06 IX+$0B lo lo lo lo Total
; IX-$05 IX+$0C hi hi hi hi Length of datablock.
; IX-$04 IX+$0D Auto - - Start Various
; IX-$03 IX+$0E Start a-z a-z addr ($80 if no autostart).
; IX-$02 IX+$0F lo - - - Length of Program
; IX-$01 IX+$10 hi - - - only i.e. without variables.
;
; ------------------------
; Canned cassette messages
; ------------------------
; The last-character-inverted Cassette messages.
; Starts with normal initial step-over byte.
;; tape-msgs
L09A1: DEFB $80
DEFM "Start tape, then press any key"
L09C0: DEFB '.'+$80
DEFB $0D
DEFM "Program:"
DEFB ' '+$80
DEFB $0D
DEFM "Number array:"
DEFB ' '+$80
DEFB $0D
DEFM "Character array:"
DEFB ' '+$80
DEFB $0D
DEFM "Bytes:"
DEFB ' '+$80
;**************************************************
;** Part 5. SCREEN AND PRINTER HANDLING ROUTINES **
;**************************************************
; --------------------------
; THE 'PRINT OUTPUT' ROUTINE
; --------------------------
; This is the routine most often used by the RST 10 restart although the
; subroutine is on two occasions called directly when it is known that
; output will definitely be to the lower screen.
;; PRINT-OUT
L09F4: CALL L0B03 ; routine PO-FETCH fetches print position
; to HL register pair.
CP $20 ; is character a space or higher ?
JP NC,L0AD9 ; jump forward to PO-ABLE if so.
CP $06 ; is character in range 00-05 ?
JR C,L0A69 ; to PO-QUEST to print '?' if so.
CP $18 ; is character in range 24d - 31d ?
JR NC,L0A69 ; to PO-QUEST to also print '?' if so.
LD HL,L0A11 - 6 ; address 0A0B - the base address of control
; character table - where zero would be.
LD E,A ; control character 06 - 23d
LD D,$00 ; is transferred to DE.
ADD HL,DE ; index into table.
LD E,(HL) ; fetch the offset to routine.
ADD HL,DE ; add to make HL the address.
PUSH HL ; push the address.
JP L0B03 ; Jump forward to PO-FETCH,
; as the screen/printer position has been
; disturbed, and then indirectly to the PO-STORE
; routine on stack.
; -----------------------------
; THE 'CONTROL CHARACTER' TABLE
; -----------------------------
; For control characters in the range 6 - 23d the following table
; is indexed to provide an offset to the handling routine that
; follows the table.
;; ctlchrtab
L0A11: DEFB L0A5F - $ ; 06d offset $4E to Address: PO-COMMA
DEFB L0A69 - $ ; 07d offset $57 to Address: PO-QUEST
DEFB L0A23 - $ ; 08d offset $10 to Address: PO-BACK-1
DEFB L0A3D - $ ; 09d offset $29 to Address: PO-RIGHT
DEFB L0A69 - $ ; 10d offset $54 to Address: PO-QUEST
DEFB L0A69 - $ ; 11d offset $53 to Address: PO-QUEST
DEFB L0A69 - $ ; 12d offset $52 to Address: PO-QUEST
DEFB L0A4F - $ ; 13d offset $37 to Address: PO-ENTER
DEFB L0A69 - $ ; 14d offset $50 to Address: PO-QUEST
DEFB L0A69 - $ ; 15d offset $4F to Address: PO-QUEST
DEFB L0A7A - $ ; 16d offset $5F to Address: PO-1-OPER
DEFB L0A7A - $ ; 17d offset $5E to Address: PO-1-OPER
DEFB L0A7A - $ ; 18d offset $5D to Address: PO-1-OPER
DEFB L0A7A - $ ; 19d offset $5C to Address: PO-1-OPER
DEFB L0A7A - $ ; 20d offset $5B to Address: PO-1-OPER
DEFB L0A7A - $ ; 21d offset $5A to Address: PO-1-OPER
DEFB L0A75 - $ ; 22d offset $54 to Address: PO-2-OPER
DEFB L0A75 - $ ; 23d offset $53 to Address: PO-2-OPER
; -------------------------
; THE 'CURSOR LEFT' ROUTINE
; -------------------------
; Backspace and up a line if that action is from the left of screen.
; For ZX printer backspace up to first column but not beyond.
;; PO-BACK-1
L0A23: INC C ; move left one column.
LD A,$22 ; value $21 is leftmost column.
CP C ; have we passed ?
JR NZ,L0A3A ; to PO-BACK-3 if not and store new position.
BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
JR NZ,L0A38 ; to PO-BACK-2 if so, as we are unable to
; backspace from the leftmost position.
INC B ; move up one screen line
LD C,$02 ; the rightmost column position.
LD A,$18 ; Note. This should be $19
; credit. Dr. Frank O'Hara, 1982
CP B ; has position moved past top of screen ?
JR NZ,L0A3A ; to PO-BACK-3 if not and store new position.
DEC B ; else back to $18.
;; PO-BACK-2
L0A38: LD C,$21 ; the leftmost column position.
;; PO-BACK-3
L0A3A: JP L0DD9 ; to CL-SET and PO-STORE to save new
; position in system variables.
; --------------------------
; THE 'CURSOR RIGHT' ROUTINE
; --------------------------
; This moves the print position to the right leaving a trail in the
; current background colour.
; "However the programmer has failed to store the new print position
; so CHR$ 9 will only work if the next print position is at a newly
; defined place.
; e.g. PRINT PAPER 2; CHR$ 9; AT 4,0;
; does work but is not very helpful"
; - Dr. Ian Logan, Understanding Your Spectrum, 1982.
;; PO-RIGHT
L0A3D: LD A,($5C91) ; fetch P_FLAG value
PUSH AF ; and save it on stack.
LD (IY+$57),$01 ; temporarily set P_FLAG 'OVER 1'.
LD A,$20 ; prepare a space.
CALL L0B65 ; routine PO-CHAR to print it.
; Note. could be PO-ABLE which would update
; the column position.
POP AF ; restore the permanent flag.
LD ($5C91),A ; and restore system variable P_FLAG
RET ; return without updating column position
; -----------------------
; Perform carriage return
; -----------------------
; A carriage return is 'printed' to screen or printer buffer.
;; PO-ENTER
L0A4F: BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
JP NZ,L0ECD ; to COPY-BUFF if so, to flush buffer and reset
; the print position.
LD C,$21 ; the leftmost column position.
CALL L0C55 ; routine PO-SCR handles any scrolling required.
DEC B ; to next screen line.
JP L0DD9 ; jump forward to CL-SET to store new position.
; -----------
; Print comma
; -----------
; The comma control character. The 32 column screen has two 16 character
; tabstops. The routine is only reached via the control character table.
;; PO-COMMA
L0A5F: CALL L0B03 ; routine PO-FETCH - seems unnecessary.
LD A,C ; the column position. $21-$01
DEC A ; move right. $20-$00
DEC A ; and again $1F-$00 or $FF if trailing
AND $10 ; will be $00 or $10.
JR L0AC3 ; forward to PO-FILL
; -------------------
; Print question mark
; -------------------
; This routine prints a question mark which is commonly
; used to print an unassigned control character in range 0-31d.
; there are a surprising number yet to be assigned.
;; PO-QUEST
L0A69: LD A,$3F ; prepare the character '?'.
JR L0AD9 ; forward to PO-ABLE.
; --------------------------------
; Control characters with operands
; --------------------------------
; Certain control characters are followed by 1 or 2 operands.
; The entry points from control character table are PO-2-OPER and PO-1-OPER.
; The routines alter the output address of the current channel so that
; subsequent RST $10 instructions take the appropriate action
; before finally resetting the output address back to PRINT-OUT.
;; PO-TV-2
L0A6D: LD DE,L0A87 ; address: PO-CONT will be next output routine
LD ($5C0F),A ; store first operand in TVDATA-hi
JR L0A80 ; forward to PO-CHANGE >>
; ---
; -> This initial entry point deals with two operands - AT or TAB.
;; PO-2-OPER
L0A75: LD DE,L0A6D ; address: PO-TV-2 will be next output routine
JR L0A7D ; forward to PO-TV-1
; ---
; -> This initial entry point deals with one operand INK to OVER.
;; PO-1-OPER
L0A7A: LD DE,L0A87 ; address: PO-CONT will be next output routine
;; PO-TV-1
L0A7D: LD ($5C0E),A ; store control code in TVDATA-lo
;; PO-CHANGE
L0A80: LD HL,($5C51) ; use CURCHL to find current output channel.
LD (HL),E ; make it
INC HL ; the supplied
LD (HL),D ; address from DE.
RET ; return.
; ---
;; PO-CONT
L0A87: LD DE,L09F4 ; Address: PRINT-OUT
CALL L0A80 ; routine PO-CHANGE to restore normal channel.
LD HL,($5C0E) ; TVDATA gives control code and possible
; subsequent character
LD D,A ; save current character
LD A,L ; the stored control code
CP $16 ; was it INK to OVER (1 operand) ?
JP C,L2211 ; to CO-TEMP-5
JR NZ,L0AC2 ; to PO-TAB if not 22d i.e. 23d TAB.
; else must have been 22d AT.
LD B,H ; line to H (0-23d)
LD C,D ; column to C (0-31d)
LD A,$1F ; the value 31d
SUB C ; reverse the column number.
JR C,L0AAC ; to PO-AT-ERR if C was greater than 31d.
ADD A,$02 ; transform to system range $02-$21
LD C,A ; and place in column register.
BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
JR NZ,L0ABF ; to PO-AT-SET as line can be ignored.
LD A,$16 ; 22 decimal
SUB B ; subtract line number to reverse
; 0 - 22 becomes 22 - 0.
;; PO-AT-ERR
L0AAC: JP C,L1E9F ; to REPORT-B if higher than 22 decimal
; Integer out of range.
INC A ; adjust for system range $01-$17
LD B,A ; place in line register
INC B ; adjust to system range $02-$18
BIT 0,(IY+$02) ; TV_FLAG - Lower screen in use ?
JP NZ,L0C55 ; exit to PO-SCR to test for scrolling
CP (IY+$31) ; Compare against DF_SZ
JP C,L0C86 ; to REPORT-5 if too low
; Out of screen.
;; PO-AT-SET
L0ABF: JP L0DD9 ; print position is valid so exit via CL-SET
; ---
; Continue here when dealing with TAB.
; Note. In BASIC, TAB is followed by a 16-bit number and was initially
; designed to work with any output device.
;; PO-TAB
L0AC2: LD A,H ; transfer parameter to A
; Losing current character -
; High byte of TAB parameter.
;; PO-FILL
L0AC3: CALL L0B03 ; routine PO-FETCH, HL-addr, BC=line/column.
; column 1 (right), $21 (left)
ADD A,C ; add operand to current column
DEC A ; range 0 - 31+
AND $1F ; make range 0 - 31d
RET Z ; return if result zero
LD D,A ; Counter to D
SET 0,(IY+$01) ; update FLAGS - signal suppress leading space.
;; PO-SPACE
L0AD0: LD A,$20 ; space character.
CALL L0C3B ; routine PO-SAVE prints the character
; using alternate set (normal output routine)
DEC D ; decrement counter.
JR NZ,L0AD0 ; to PO-SPACE until done
RET ; return
; ----------------------
; Printable character(s)
; ----------------------
; This routine prints printable characters and continues into
; the position store routine
;; PO-ABLE
L0AD9: CALL L0B24 ; routine PO-ANY
; and continue into position store routine.
; ----------------------------
; THE 'POSITION STORE' ROUTINE
; ----------------------------
; This routine updates the system variables associated with the main screen,
; the lower screen/input buffer or the ZX printer.
;; PO-STORE
L0ADC: BIT 1,(IY+$01) ; Test FLAGS - is printer in use ?
JR NZ,L0AFC ; Forward, if so, to PO-ST-PR
BIT 0,(IY+$02) ; Test TV_FLAG - is lower screen in use ?
JR NZ,L0AF0 ; Forward, if so, to PO-ST-E
; This section deals with the upper screen.
LD ($5C88),BC ; Update S_POSN - line/column upper screen
LD ($5C84),HL ; Update DF_CC - upper display file address
RET ; Return.
; ---
; This section deals with the lower screen.
;; PO-ST-E
L0AF0: LD ($5C8A),BC ; Update SPOSNL line/column lower screen
LD ($5C82),BC ; Update ECHO_E line/column input buffer
LD ($5C86),HL ; Update DFCCL lower screen memory address
RET ; Return.
; ---
; This section deals with the ZX Printer.
;; PO-ST-PR
L0AFC: LD (IY+$45),C ; Update P_POSN column position printer
LD ($5C80),HL ; Update PR_CC - full printer buffer memory
; address
RET ; Return.
; Note. that any values stored in location 23681 will be overwritten with
; the value 91 decimal.
; Credit April 1983, Dilwyn Jones. "Delving Deeper into your ZX Spectrum".
; ----------------------------
; THE 'POSITION FETCH' ROUTINE
; ----------------------------
; This routine fetches the line/column and display file address of the upper
; and lower screen or, if the printer is in use, the column position and
; absolute memory address.
; Note. that PR-CC-hi (23681) is used by this routine and if, in accordance
; with the manual (that says this is unused), the location has been used for
; other purposes, then subsequent output to the printer buffer could corrupt
; a 256-byte section of memory.
;; PO-FETCH
L0B03: BIT 1,(IY+$01) ; Test FLAGS - is printer in use ?
JR NZ,L0B1D ; Forward, if so, to PO-F-PR
; assume upper screen in use and thus optimize for path that requires speed.
LD BC,($5C88) ; Fetch line/column from S_POSN
LD HL,($5C84) ; Fetch DF_CC display file address
BIT 0,(IY+$02) ; Test TV_FLAG - lower screen in use ?
RET Z ; Return if upper screen in use.
; Overwrite registers with values for lower screen.
LD BC,($5C8A) ; Fetch line/column from SPOSNL
LD HL,($5C86) ; Fetch display file address from DFCCL
RET ; Return.
; ---
; This section deals with the ZX Printer.
;; PO-F-PR
L0B1D: LD C,(IY+$45) ; Fetch column from P_POSN.
LD HL,($5C80) ; Fetch printer buffer address from PR_CC.
RET ; Return.
; ---------------------------------
; THE 'PRINT ANY CHARACTER' ROUTINE
; ---------------------------------
; This routine is used to print any character in range 32d - 255d
; It is only called from PO-ABLE which continues into PO-STORE
;; PO-ANY
L0B24: CP $80 ; ASCII ?
JR C,L0B65 ; to PO-CHAR is so.
CP $90 ; test if a block graphic character.
JR NC,L0B52 ; to PO-T&UDG to print tokens and UDGs
; The 16 2*2 mosaic characters 128-143 decimal are formed from
; bits 0-3 of the character.
LD B,A ; save character
CALL L0B38 ; routine PO-GR-1 to construct top half
; then bottom half.
CALL L0B03 ; routine PO-FETCH fetches print position.
LD DE,$5C92 ; MEM-0 is location of 8 bytes of character
JR L0B7F ; to PR-ALL to print to screen or printer
; ---
;; PO-GR-1
L0B38: LD HL,$5C92 ; address MEM-0 - a temporary buffer in
; systems variables which is normally used
; by the calculator.
CALL L0B3E ; routine PO-GR-2 to construct top half
; and continue into routine to construct
; bottom half.
;; PO-GR-2
L0B3E: RR B ; rotate bit 0/2 to carry
SBC A,A ; result $00 or $FF
AND $0F ; mask off right hand side
LD C,A ; store part in C
RR B ; rotate bit 1/3 of original chr to carry
SBC A,A ; result $00 or $FF
AND $F0 ; mask off left hand side
OR C ; combine with stored pattern
LD C,$04 ; four bytes for top/bottom half
;; PO-GR-3
L0B4C: LD (HL),A ; store bit patterns in temporary buffer
INC HL ; next address
DEC C ; jump back to
JR NZ,L0B4C ; to PO-GR-3 until byte is stored 4 times
RET ; return
; ---
; Tokens and User defined graphics are now separated.
;; PO-T&UDG
L0B52: SUB $A5 ; the 'RND' character
JR NC,L0B5F ; to PO-T to print tokens
ADD A,$15 ; add 21d to restore to 0 - 20
PUSH BC ; save current print position
LD BC,($5C7B) ; fetch UDG to address bit patterns
JR L0B6A ; to PO-CHAR-2 - common code to lay down
; a bit patterned character
; ---
;; PO-T
L0B5F: CALL L0C10 ; routine PO-TOKENS prints tokens
JP L0B03 ; exit via a JUMP to PO-FETCH as this routine
; must continue into PO-STORE.
; A JR instruction could be used.
; This point is used to print ASCII characters 32d - 127d.
;; PO-CHAR
L0B65: PUSH BC ; save print position
LD BC,($5C36) ; address CHARS
; This common code is used to transfer the character bytes to memory.
;; PO-CHAR-2
L0B6A: EX DE,HL ; transfer destination address to DE
LD HL,$5C3B ; point to FLAGS
RES 0,(HL) ; allow for leading space
CP $20 ; is it a space ?
JR NZ,L0B76 ; to PO-CHAR-3 if not
SET 0,(HL) ; signal no leading space to FLAGS
;; PO-CHAR-3
L0B76: LD H,$00 ; set high byte to 0
LD L,A ; character to A
; 0-21 UDG or 32-127 ASCII.
ADD HL,HL ; multiply
ADD HL,HL ; by
ADD HL,HL ; eight
ADD HL,BC ; HL now points to first byte of character
POP BC ; the source address CHARS or UDG
EX DE,HL ; character address to DE
; ----------------------------------
; THE 'PRINT ALL CHARACTERS' ROUTINE
; ----------------------------------
; This entry point entered from above to print ASCII and UDGs but also from
; earlier to print mosaic characters.
; HL=destination
; DE=character source
; BC=line/column
;; PR-ALL
L0B7F: LD A,C ; column to A
DEC A ; move right
LD A,$21 ; pre-load with leftmost position
JR NZ,L0B93 ; but if not zero to PR-ALL-1
DEC B ; down one line
LD C,A ; load C with $21
BIT 1,(IY+$01) ; test FLAGS - Is printer in use
JR Z,L0B93 ; to PR-ALL-1 if not
PUSH DE ; save source address
CALL L0ECD ; routine COPY-BUFF outputs line to printer
POP DE ; restore character source address
LD A,C ; the new column number ($21) to C
;; PR-ALL-1
L0B93: CP C ; this test is really for screen - new line ?
PUSH DE ; save source
CALL Z,L0C55 ; routine PO-SCR considers scrolling
POP DE ; restore source
PUSH BC ; save line/column
PUSH HL ; and destination
LD A,($5C91) ; fetch P_FLAG to accumulator
LD B,$FF ; prepare OVER mask in B.
RRA ; bit 0 set if OVER 1
JR C,L0BA4 ; to PR-ALL-2
INC B ; set OVER mask to 0
;; PR-ALL-2
L0BA4: RRA ; skip bit 1 of P_FLAG
RRA ; bit 2 is INVERSE
SBC A,A ; will be FF for INVERSE 1 else zero
LD C,A ; transfer INVERSE mask to C
LD A,$08 ; prepare to count 8 bytes
AND A ; clear carry to signal screen
BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
JR Z,L0BB6 ; to PR-ALL-3 if screen
SET 1,(IY+$30) ; update FLAGS2 - signal printer buffer has
; been used.
SCF ; set carry flag to signal printer.
;; PR-ALL-3
L0BB6: EX DE,HL ; now HL=source, DE=destination
;; PR-ALL-4
L0BB7: EX AF,AF' ; save printer/screen flag
LD A,(DE) ; fetch existing destination byte
AND B ; consider OVER
XOR (HL) ; now XOR with source
XOR C ; now with INVERSE MASK
LD (DE),A ; update screen/printer
EX AF,AF' ; restore flag
JR C,L0BD3 ; to PR-ALL-6 - printer address update
INC D ; gives next pixel line down screen
;; PR-ALL-5
L0BC1: INC HL ; address next character byte
DEC A ; the byte count is decremented
JR NZ,L0BB7 ; back to PR-ALL-4 for all 8 bytes
EX DE,HL ; destination to HL
DEC H ; bring back to last updated screen position
BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
CALL Z,L0BDB ; if not, call routine PO-ATTR to update
; corresponding colour attribute.
POP HL ; restore original screen/printer position
POP BC ; and line column
DEC C ; move column to right
INC HL ; increase screen/printer position
RET ; return and continue into PO-STORE
; within PO-ABLE
; ---
; This branch is used to update the printer position by 32 places
; Note. The high byte of the address D remains constant (which it should).
;; PR-ALL-6
L0BD3: EX AF,AF' ; save the flag
LD A,$20 ; load A with 32 decimal
ADD A,E ; add this to E
LD E,A ; and store result in E
EX AF,AF' ; fetch the flag
JR L0BC1 ; back to PR-ALL-5
; -----------------------------------
; THE 'GET ATTRIBUTE ADDRESS' ROUTINE
; -----------------------------------
; This routine is entered with the HL register holding the last screen
; address to be updated by PRINT or PLOT.
; The Spectrum screen arrangement leads to the L register holding the correct
; value for the attribute file and it is only necessary to manipulate H to
; form the correct colour attribute address.
;; PO-ATTR
L0BDB: LD A,H ; fetch high byte $40 - $57
RRCA ; shift
RRCA ; bits 3 and 4
RRCA ; to right.
AND $03 ; range is now 0 - 2
OR $58 ; form correct high byte for third of screen
LD H,A ; HL is now correct
LD DE,($5C8F) ; make D hold ATTR_T, E hold MASK-T
LD A,(HL) ; fetch existing attribute
XOR E ; apply masks
AND D ;
XOR E ;
BIT 6,(IY+$57) ; test P_FLAG - is this PAPER 9 ??
JR Z,L0BFA ; skip to PO-ATTR-1 if not.
AND $C7 ; set paper
BIT 2,A ; to contrast with ink
JR NZ,L0BFA ; skip to PO-ATTR-1
XOR $38 ;
;; PO-ATTR-1
L0BFA: BIT 4,(IY+$57) ; test P_FLAG - Is this INK 9 ??
JR Z,L0C08 ; skip to PO-ATTR-2 if not
AND $F8 ; make ink
BIT 5,A ; contrast with paper.
JR NZ,L0C08 ; to PO-ATTR-2
XOR $07 ;
;; PO-ATTR-2
L0C08: LD (HL),A ; save the new attribute.
RET ; return.
; ---------------------------------
; THE 'MESSAGE PRINTING' SUBROUTINE
; ---------------------------------
; This entry point is used to print tape, boot-up, scroll? and error messages.
; On entry the DE register points to an initial step-over byte or the
; inverted end-marker of the previous entry in the table.
; Register A contains the message number, often zero to print first message.
; (HL has nothing important usually P_FLAG)
;; PO-MSG
L0C0A: PUSH HL ; put hi-byte zero on stack to suppress
LD H,$00 ; trailing spaces
EX (SP),HL ; ld h,0; push hl would have done ?.
JR L0C14 ; forward to PO-TABLE.
; ---
; This entry point prints the BASIC keywords, '<>' etc. from alt set
;; PO-TOKENS
L0C10: LD DE,L0095 ; address: TKN-TABLE
PUSH AF ; save the token number to control
; trailing spaces - see later *
; ->
;; PO-TABLE
L0C14: CALL L0C41 ; routine PO-SEARCH will set carry for
; all messages and function words.
JR C,L0C22 ; forward to PO-EACH if not a command, '<>' etc.
LD A,$20 ; prepare leading space
BIT 0,(IY+$01) ; test FLAGS - leading space if not set
CALL Z,L0C3B ; routine PO-SAVE to print a space without
; disturbing registers.
;; PO-EACH
L0C22: LD A,(DE) ; Fetch character from the table.
AND $7F ; Cancel any inverted bit.
CALL L0C3B ; Routine PO-SAVE to print using the alternate
; set of registers.
LD A,(DE) ; Re-fetch character from table.
INC DE ; Address next character in the table.
ADD A,A ; Was character inverted ?
; (this also doubles character)
JR NC,L0C22 ; back to PO-EACH if not.
POP DE ; * re-fetch trailing space byte to D
CP $48 ; was the last character '$' ?
JR Z,L0C35 ; forward to PO-TR-SP to consider trailing
; space if so.
CP $82 ; was it < 'A' i.e. '#','>','=' from tokens
; or ' ','.' (from tape) or '?' from scroll
RET C ; Return if so as no trailing space required.
;; PO-TR-SP
L0C35: LD A,D ; The trailing space flag (zero if an error msg)
CP $03 ; Test against RND, INKEY$ and PI which have no
; parameters and therefore no trailing space.
RET C ; Return if no trailing space.
LD A,$20 ; Prepare the space character and continue to
; print and make an indirect return.
; -----------------------------------
; THE 'RECURSIVE PRINTING' SUBROUTINE
; -----------------------------------
; This routine which is part of PRINT-OUT allows RST $10 to be used
; recursively to print tokens and the spaces associated with them.
; It is called on three occasions when the value of DE must be preserved.
;; PO-SAVE
L0C3B: PUSH DE ; Save DE value.
EXX ; Switch in main set
RST 10H ; PRINT-A prints using this alternate set.
EXX ; Switch back to this alternate set.
POP DE ; Restore the initial DE value.
RET ; Return.
; ------------
; Table search
; ------------
; This subroutine searches a message or the token table for the
; message number held in A. DE holds the address of the table.
;; PO-SEARCH
L0C41: PUSH AF ; save the message/token number
EX DE,HL ; transfer DE to HL
INC A ; adjust for initial step-over byte
;; PO-STEP
L0C44: BIT 7,(HL) ; is character inverted ?
INC HL ; address next
JR Z,L0C44 ; back to PO-STEP if not inverted.
DEC A ; decrease counter
JR NZ,L0C44 ; back to PO-STEP if not zero
EX DE,HL ; transfer address to DE
POP AF ; restore message/token number
CP $20 ; return with carry set
RET C ; for all messages and function tokens
LD A,(DE) ; test first character of token
SUB $41 ; and return with carry set
RET ; if it is less that 'A'
; i.e. '<>', '<=', '>='
; ---------------
; Test for scroll
; ---------------
; This test routine is called when printing carriage return, when considering
; PRINT AT and from the general PRINT ALL characters routine to test if
; scrolling is required, prompting the user if necessary.
; This is therefore using the alternate set.
; The B register holds the current line.
;; PO-SCR
L0C55: BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
RET NZ ; return immediately if so.
LD DE,L0DD9 ; set DE to address: CL-SET
PUSH DE ; and push for return address.
LD A,B ; transfer the line to A.
BIT 0,(IY+$02) ; test TV_FLAG - lower screen in use ?
JP NZ,L0D02 ; jump forward to PO-SCR-4 if so.
CP (IY+$31) ; greater than DF_SZ display file size ?
JR C,L0C86 ; forward to REPORT-5 if less.
; 'Out of screen'
RET NZ ; return (via CL-SET) if greater
BIT 4,(IY+$02) ; test TV_FLAG - Automatic listing ?
JR Z,L0C88 ; forward to PO-SCR-2 if not.
LD E,(IY+$2D) ; fetch BREG - the count of scroll lines to E.
DEC E ; decrease and jump
JR Z,L0CD2 ; to PO-SCR-3 if zero and scrolling required.
LD A,$00 ; explicit - select channel zero.
CALL L1601 ; routine CHAN-OPEN opens it.
LD SP,($5C3F) ; set stack pointer to LIST_SP
RES 4,(IY+$02) ; reset TV_FLAG - signal auto listing finished.
RET ; return ignoring pushed value, CL-SET
; to MAIN or EDITOR without updating
; print position >>
; ---
;; REPORT-5
L0C86: RST 08H ; ERROR-1
DEFB $04 ; Error Report: Out of screen
; continue here if not an automatic listing.
;; PO-SCR-2
L0C88: DEC (IY+$52) ; decrease SCR_CT
JR NZ,L0CD2 ; forward to PO-SCR-3 to scroll display if
; result not zero.
; now produce prompt.
LD A,$18 ; reset
SUB B ; the
LD ($5C8C),A ; SCR_CT scroll count
LD HL,($5C8F) ; L=ATTR_T, H=MASK_T
PUSH HL ; save on stack
LD A,($5C91) ; P_FLAG
PUSH AF ; save on stack to prevent lower screen
; attributes (BORDCR etc.) being applied.
LD A,$FD ; select system channel 'K'
CALL L1601 ; routine CHAN-OPEN opens it
XOR A ; clear to address message directly
LD DE,L0CF8 ; make DE address: scrl-mssg
CALL L0C0A ; routine PO-MSG prints to lower screen
SET 5,(IY+$02) ; set TV_FLAG - signal lower screen requires
; clearing
LD HL,$5C3B ; make HL address FLAGS
SET 3,(HL) ; signal 'L' mode.
RES 5,(HL) ; signal 'no new key'.
EXX ; switch to main set.
; as calling chr input from alternative set.
CALL L15D4 ; routine WAIT-KEY waits for new key
; Note. this is the right routine but the
; stream in use is unsatisfactory. From the
; choices available, it is however the best.
EXX ; switch back to alternate set.
CP $20 ; space is considered as BREAK
JR Z,L0D00 ; forward to REPORT-D if so
; 'BREAK - CONT repeats'
CP $E2 ; is character 'STOP' ?
JR Z,L0D00 ; forward to REPORT-D if so
OR $20 ; convert to lower-case
CP $6E ; is character 'n' ?
JR Z,L0D00 ; forward to REPORT-D if so else scroll.
LD A,$FE ; select system channel 'S'
CALL L1601 ; routine CHAN-OPEN
POP AF ; restore original P_FLAG
LD ($5C91),A ; and save in P_FLAG.
POP HL ; restore original ATTR_T, MASK_T
LD ($5C8F),HL ; and reset ATTR_T, MASK-T as 'scroll?' has
; been printed.
;; PO-SCR-3
L0CD2: CALL L0DFE ; routine CL-SC-ALL to scroll whole display
LD B,(IY+$31) ; fetch DF_SZ to B
INC B ; increase to address last line of display
LD C,$21 ; set C to $21 (was $21 from above routine)
PUSH BC ; save the line and column in BC.
CALL L0E9B ; routine CL-ADDR finds display address.
LD A,H ; now find the corresponding attribute byte
RRCA ; (this code sequence is used twice
RRCA ; elsewhere and is a candidate for
RRCA ; a subroutine.)
AND $03 ;
OR $58 ;
LD H,A ;
LD DE,$5AE0 ; start of last 'line' of attribute area
LD A,(DE) ; get attribute for last line
LD C,(HL) ; transfer to base line of upper part
LD B,$20 ; there are thirty two bytes
EX DE,HL ; swap the pointers.
;; PO-SCR-3A
L0CF0: LD (DE),A ; transfer
LD (HL),C ; attributes.
INC DE ; address next.
INC HL ; address next.
DJNZ L0CF0 ; loop back to PO-SCR-3A for all adjacent
; attribute lines.
POP BC ; restore the line/column.
RET ; return via CL-SET (was pushed on stack).
; ---
; The message 'scroll?' appears here with last byte inverted.
;; scrl-mssg
L0CF8: DEFB $80 ; initial step-over byte.
DEFM "scroll"
DEFB '?'+$80
;; REPORT-D
L0D00: RST 08H ; ERROR-1
DEFB $0C ; Error Report: BREAK - CONT repeats
; continue here if using lower display - A holds line number.
;; PO-SCR-4
L0D02: CP $02 ; is line number less than 2 ?
JR C,L0C86 ; to REPORT-5 if so
; 'Out of Screen'.
ADD A,(IY+$31) ; add DF_SZ
SUB $19 ;
RET NC ; return if scrolling unnecessary
NEG ; Negate to give number of scrolls required.
PUSH BC ; save line/column
LD B,A ; count to B
LD HL,($5C8F) ; fetch current ATTR_T, MASK_T to HL.
PUSH HL ; and save
LD HL,($5C91) ; fetch P_FLAG
PUSH HL ; and save.
; to prevent corruption by input AT
CALL L0D4D ; routine TEMPS sets to BORDCR etc
LD A,B ; transfer scroll number to A.
;; PO-SCR-4A
L0D1C: PUSH AF ; save scroll number.
LD HL,$5C6B ; address DF_SZ
LD B,(HL) ; fetch old value
LD A,B ; transfer to A
INC A ; and increment
LD (HL),A ; then put back.
LD HL,$5C89 ; address S_POSN_hi - line
CP (HL) ; compare
JR C,L0D2D ; forward to PO-SCR-4B if scrolling required
INC (HL) ; else increment S_POSN_hi
LD B,$18 ; set count to whole display ??
; Note. should be $17 and the top line will be
; scrolled into the ROM which is harmless on
; the standard set up.
; credit P.Giblin 1984.
;; PO-SCR-4B
L0D2D: CALL L0E00 ; routine CL-SCROLL scrolls B lines
POP AF ; restore scroll counter.
DEC A ; decrease
JR NZ,L0D1C ; back to PO-SCR-4A until done
POP HL ; restore original P_FLAG.
LD (IY+$57),L ; and overwrite system variable P_FLAG.
POP HL ; restore original ATTR_T/MASK_T.
LD ($5C8F),HL ; and update system variables.
LD BC,($5C88) ; fetch S_POSN to BC.
RES 0,(IY+$02) ; signal to TV_FLAG - main screen in use.
CALL L0DD9 ; call routine CL-SET for upper display.
SET 0,(IY+$02) ; signal to TV_FLAG - lower screen in use.
POP BC ; restore line/column
RET ; return via CL-SET for lower display.
; ----------------------
; Temporary colour items
; ----------------------
; This subroutine is called 11 times to copy the permanent colour items
; to the temporary ones.
;; TEMPS
L0D4D: XOR A ; clear the accumulator
LD HL,($5C8D) ; fetch L=ATTR_P and H=MASK_P
BIT 0,(IY+$02) ; test TV_FLAG - is lower screen in use ?
JR Z,L0D5B ; skip to TEMPS-1 if not
LD H,A ; set H, MASK P, to 00000000.
LD L,(IY+$0E) ; fetch BORDCR to L which is used for lower
; screen.
;; TEMPS-1
L0D5B: LD ($5C8F),HL ; transfer values to ATTR_T and MASK_T
; for the print flag the permanent values are odd bits, temporary even bits.
LD HL,$5C91 ; address P_FLAG.
JR NZ,L0D65 ; skip to TEMPS-2 if lower screen using A=0.
LD A,(HL) ; else pick up flag bits.
RRCA ; rotate permanent bits to temporary bits.
;; TEMPS-2
L0D65: XOR (HL) ;
AND $55 ; BIN 01010101
XOR (HL) ; permanent now as original
LD (HL),A ; apply permanent bits to temporary bits.
RET ; and return.
; -----------------
; THE 'CLS' COMMAND
; -----------------
; This command clears the display.
; The routine is also called during initialization and by the CLEAR command.
; If it's difficult to write it should be difficult to read.
;; CLS
L0D6B: CALL L0DAF ; Routine CL-ALL clears the entire display and
; sets the attributes to the permanent ones
; from ATTR-P.
; Having cleared all 24 lines of the display area, continue into the
; subroutine that clears the lower display area. Note that at the moment
; the attributes for the lower lines are the same as upper ones and have
; to be changed to match the BORDER colour.
; --------------------------
; THE 'CLS-LOWER' SUBROUTINE
; --------------------------
; This routine is called from INPUT, and from the MAIN execution loop.
; This is very much a housekeeping routine which clears between 2 and 23
; lines of the display, setting attributes and correcting situations where
; errors have occurred while the normal input and output routines have been
; temporarily diverted to deal with, say colour control codes.
;; CLS-LOWER
L0D6E: LD HL,$5C3C ; address System Variable TV_FLAG.
RES 5,(HL) ; TV_FLAG - signal do not clear lower screen.
SET 0,(HL) ; TV_FLAG - signal lower screen in use.
CALL L0D4D ; routine TEMPS applies permanent attributes,
; in this case BORDCR to ATTR_T.
; Note. this seems unnecessary and is repeated
; within CL-LINE.
LD B,(IY+$31) ; fetch lower screen display file size DF_SZ
CALL L0E44 ; routine CL-LINE clears lines to bottom of the
; display and sets attributes from BORDCR while
; preserving the B register.
LD HL,$5AC0 ; set initial attribute address to the leftmost
; cell of second line up.
LD A,($5C8D) ; fetch permanent attribute from ATTR_P.
DEC B ; decrement lower screen display file size.
JR L0D8E ; forward to enter the backfill loop at CLS-3
; where B is decremented again.
; ---
; The backfill loop is entered at midpoint and ensures, if more than 2
; lines have been cleared, that any other lines take the permanent screen
; attributes.
;; CLS-1
L0D87: LD C,$20 ; set counter to 32 character cells per line
;; CLS-2
L0D89: DEC HL ; decrease attribute address.
LD (HL),A ; and place attributes in next line up.
DEC C ; decrease the 32 counter.
JR NZ,L0D89 ; loop back to CLS-2 until all 32 cells done.
;; CLS-3
L0D8E: DJNZ L0D87 ; decrease B counter and back to CLS-1
; if not zero.
LD (IY+$31),$02 ; now set DF_SZ lower screen to 2
; This entry point is also called from CL-ALL below to
; reset the system channel input and output addresses to normal.
;; CL-CHAN
L0D94: LD A,$FD ; select system channel 'K'
CALL L1601 ; routine CHAN-OPEN opens it.
LD HL,($5C51) ; fetch CURCHL to HL to address current channel
LD DE,L09F4 ; set address to PRINT-OUT for first pass.
AND A ; clear carry for first pass.
;; CL-CHAN-A
L0DA0: LD (HL),E ; Insert the output address on the first pass
INC HL ; or the input address on the second pass.
LD (HL),D ;
INC HL ;
LD DE,L10A8 ; fetch address KEY-INPUT for second pass
CCF ; complement carry flag - will set on pass 1.
JR C,L0DA0 ; back to CL-CHAN-A if first pass else done.
LD BC,$1721 ; line 23 for lower screen
JR L0DD9 ; exit via CL-SET to set column
; for lower display
; ---------------------------
; Clearing whole display area
; ---------------------------
; This subroutine called from CLS, AUTO-LIST and MAIN-3
; clears 24 lines of the display and resets the relevant system variables.
; This routine also recovers from an error situation where, for instance, an
; invalid colour or position control code has left the output routine addressing
; PO-TV-2 or PO-CONT.
;; CL-ALL
L0DAF: LD HL,$0000 ; Initialize plot coordinates.
LD ($5C7D),HL ; Set system variable COORDS to 0,0.
RES 0,(IY+$30) ; update FLAGS2 - signal main screen is clear.
CALL L0D94 ; routine CL-CHAN makes channel 'K' 'normal'.
LD A,$FE ; select system channel 'S'
CALL L1601 ; routine CHAN-OPEN opens it.
CALL L0D4D ; routine TEMPS applies permanent attributes,
; in this case ATTR_P, to ATTR_T.
; Note. this seems unnecessary.
LD B,$18 ; There are 24 lines.
CALL L0E44 ; routine CL-LINE clears 24 text lines and sets
; attributes from ATTR-P.
; This routine preserves B and sets C to $21.
LD HL,($5C51) ; fetch CURCHL make HL address output routine.
LD DE,L09F4 ; address: PRINT-OUT
LD (HL),E ; is made
INC HL ; the normal
LD (HL),D ; output address.
LD (IY+$52),$01 ; set SCR_CT - scroll count - to default.
; Note. BC already contains $1821.
LD BC,$1821 ; reset column and line to 0,0
; and continue into CL-SET, below, exiting
; via PO-STORE (for the upper screen).
; --------------------
; THE 'CL-SET' ROUTINE
; --------------------
; This important subroutine is used to calculate the character output
; address for screens or printer based on the line/column for screens
; or the column for printer.
;; CL-SET
L0DD9: LD HL,$5B00 ; the base address of printer buffer
BIT 1,(IY+$01) ; test FLAGS - is printer in use ?
JR NZ,L0DF4 ; forward to CL-SET-2 if so.
LD A,B ; transfer line to A.
BIT 0,(IY+$02) ; test TV_FLAG - lower screen in use ?
JR Z,L0DEE ; skip to CL-SET-1 if handling upper part
ADD A,(IY+$31) ; add DF_SZ for lower screen
SUB $18 ; and adjust.
;; CL-SET-1
L0DEE: PUSH BC ; save the line/column.
LD B,A ; transfer line to B
; (adjusted if lower screen)
CALL L0E9B ; routine CL-ADDR calculates address at left
; of screen.
POP BC ; restore the line/column.
;; CL-SET-2
L0DF4: LD A,$21 ; the column $01-$21 is reversed
SUB C ; to range $00 - $20
LD E,A ; now transfer to DE
LD D,$00 ; prepare for addition
ADD HL,DE ; and add to base address
JP L0ADC ; exit via PO-STORE to update the relevant
; system variables.
; ----------------
; Handle scrolling
; ----------------
; The routine CL-SC-ALL is called once from PO to scroll all the display
; and from the routine CL-SCROLL, once, to scroll part of the display.
;; CL-SC-ALL
L0DFE: LD B,$17 ; scroll 23 lines, after 'scroll?'.
;; CL-SCROLL
L0E00: CALL L0E9B ; routine CL-ADDR gets screen address in HL.
LD C,$08 ; there are 8 pixel lines to scroll.
;; CL-SCR-1
L0E05: PUSH BC ; save counters.
PUSH HL ; and initial address.
LD A,B ; get line count.
AND $07 ; will set zero if all third to be scrolled.
LD A,B ; re-fetch the line count.
JR NZ,L0E19 ; forward to CL-SCR-3 if partial scroll.
; HL points to top line of third and must be copied to bottom of previous 3rd.
; ( so HL = $4800 or $5000 ) ( but also sometimes $4000 )
;; CL-SCR-2
L0E0D: EX DE,HL ; copy HL to DE.
LD HL,$F8E0 ; subtract $08 from H and add $E0 to L -
ADD HL,DE ; to make destination bottom line of previous
; third.
EX DE,HL ; restore the source and destination.
LD BC,$0020 ; thirty-two bytes are to be copied.
DEC A ; decrement the line count.
LDIR ; copy a pixel line to previous third.
;; CL-SCR-3
L0E19: EX DE,HL ; save source in DE.
LD HL,$FFE0 ; load the value -32.
ADD HL,DE ; add to form destination in HL.
EX DE,HL ; switch source and destination
LD B,A ; save the count in B.
AND $07 ; mask to find count applicable to current
RRCA ; third and
RRCA ; multiply by
RRCA ; thirty two (same as 5 RLCAs)
LD C,A ; transfer byte count to C ($E0 at most)
LD A,B ; store line count to A
LD B,$00 ; make B zero
LDIR ; copy bytes (BC=0, H incremented, L=0)
LD B,$07 ; set B to 7, C is zero.
ADD HL,BC ; add 7 to H to address next third.
AND $F8 ; has last third been done ?
JR NZ,L0E0D ; back to CL-SCR-2 if not.
POP HL ; restore topmost address.
INC H ; next pixel line down.
POP BC ; restore counts.
DEC C ; reduce pixel line count.
JR NZ,L0E05 ; back to CL-SCR-1 if all eight not done.
CALL L0E88 ; routine CL-ATTR gets address in attributes
; from current 'ninth line', count in BC.
LD HL,$FFE0 ; set HL to the 16-bit value -32.
ADD HL,DE ; and add to form destination address.
EX DE,HL ; swap source and destination addresses.
LDIR ; copy bytes scrolling the linear attributes.
LD B,$01 ; continue to clear the bottom line.
; ------------------------------
; THE 'CLEAR TEXT LINES' ROUTINE
; ------------------------------
; This subroutine, called from CL-ALL, CLS-LOWER and AUTO-LIST and above,
; clears text lines at bottom of display.
; The B register holds on entry the number of lines to be cleared 1-24.
;; CL-LINE
L0E44: PUSH BC ; save line count
CALL L0E9B ; routine CL-ADDR gets top address
LD C,$08 ; there are eight screen lines to a text line.
;; CL-LINE-1
L0E4A: PUSH BC ; save pixel line count
PUSH HL ; and save the address
LD A,B ; transfer the line to A (1-24).
;; CL-LINE-2
L0E4D: AND $07 ; mask 0-7 to consider thirds at a time
RRCA ; multiply
RRCA ; by 32 (same as five RLCA instructions)
RRCA ; now 32 - 256(0)
LD C,A ; store result in C
LD A,B ; save line in A (1-24)
LD B,$00 ; set high byte to 0, prepare for ldir.
DEC C ; decrement count 31-255.
LD D,H ; copy HL
LD E,L ; to DE.
LD (HL),$00 ; blank the first byte.
INC DE ; make DE point to next byte.
LDIR ; ldir will clear lines.
LD DE,$0701 ; now address next third adjusting
ADD HL,DE ; register E to address left hand side
DEC A ; decrease the line count.
AND $F8 ; will be 16, 8 or 0 (AND $18 will do).
LD B,A ; transfer count to B.
JR NZ,L0E4D ; back to CL-LINE-2 if 16 or 8 to do
; the next third.
POP HL ; restore start address.
INC H ; address next line down.
POP BC ; fetch counts.
DEC C ; decrement pixel line count
JR NZ,L0E4A ; back to CL-LINE-1 till all done.
CALL L0E88 ; routine CL-ATTR gets attribute address
; in DE and B * 32 in BC.
LD H,D ; transfer the address
LD L,E ; to HL.
INC DE ; make DE point to next location.
LD A,($5C8D) ; fetch ATTR_P - permanent attributes
BIT 0,(IY+$02) ; test TV_FLAG - lower screen in use ?
JR Z,L0E80 ; skip to CL-LINE-3 if not.
LD A,($5C48) ; else lower screen uses BORDCR as attribute.
;; CL-LINE-3
L0E80: LD (HL),A ; put attribute in first byte.
DEC BC ; decrement the counter.
LDIR ; copy bytes to set all attributes.
POP BC ; restore the line $01-$24.
LD C,$21 ; make column $21. (No use is made of this)
RET ; return to the calling routine.
; ------------------
; Attribute handling
; ------------------
; This subroutine is called from CL-LINE or CL-SCROLL with the HL register
; pointing to the 'ninth' line and H needs to be decremented before or after
; the division. Had it been done first then either present code or that used
; at the start of PO-ATTR could have been used.
; The Spectrum screen arrangement leads to the L register already holding
; the correct value for the attribute file and it is only necessary
; to manipulate H to form the correct colour attribute address.
;; CL-ATTR
L0E88: LD A,H ; fetch H to A - $48, $50, or $58.
RRCA ; divide by
RRCA ; eight.
RRCA ; $09, $0A or $0B.
DEC A ; $08, $09 or $0A.
OR $50 ; $58, $59 or $5A.
LD H,A ; save high byte of attributes.
EX DE,HL ; transfer attribute address to DE
LD H,C ; set H to zero - from last LDIR.
LD L,B ; load L with the line from B.
ADD HL,HL ; multiply
ADD HL,HL ; by
ADD HL,HL ; thirty two
ADD HL,HL ; to give count of attribute
ADD HL,HL ; cells to the end of display.
LD B,H ; transfer the result
LD C,L ; to register BC.
RET ; return.
; -------------------------------
; Handle display with line number
; -------------------------------
; This subroutine is called from four places to calculate the address
; of the start of a screen character line which is supplied in B.
;; CL-ADDR
L0E9B: LD A,$18 ; reverse the line number
SUB B ; to range $00 - $17.
LD D,A ; save line in D for later.
RRCA ; multiply
RRCA ; by
RRCA ; thirty-two.
AND $E0 ; mask off low bits to make
LD L,A ; L a multiple of 32.
LD A,D ; bring back the line to A.
AND $18 ; now $00, $08 or $10.
OR $40 ; add the base address of screen.
LD H,A ; HL now has the correct address.
RET ; return.
; -------------------
; Handle COPY command
; -------------------
; This command copies the top 176 lines to the ZX Printer
; It is popular to call this from machine code at point
; L0EAF with B holding 192 (and interrupts disabled) for a full-screen
; copy. This particularly applies to 16K Spectrums as time-critical
; machine code routines cannot be written in the first 16K of RAM as
; it is shared with the ULA which has precedence over the Z80 chip.
;; COPY
L0EAC: DI ; disable interrupts as this is time-critical.
LD B,$B0 ; top 176 lines.
L0EAF: LD HL,$4000 ; address start of the display file.
; now enter a loop to handle each pixel line.
;; COPY-1
L0EB2: PUSH HL ; save the screen address.
PUSH BC ; and the line counter.
CALL L0EF4 ; routine COPY-LINE outputs one line.
POP BC ; restore the line counter.
POP HL ; and display address.
INC H ; next line down screen within 'thirds'.
LD A,H ; high byte to A.
AND $07 ; result will be zero if we have left third.
JR NZ,L0EC9 ; forward to COPY-2 if not to continue loop.
LD A,L ; consider low byte first.
ADD A,$20 ; increase by 32 - sets carry if back to zero.
LD L,A ; will be next group of 8.
CCF ; complement - carry set if more lines in
; the previous third.
SBC A,A ; will be FF, if more, else 00.
AND $F8 ; will be F8 (-8) or 00.
ADD A,H ; that is subtract 8, if more to do in third.
LD H,A ; and reset address.
;; COPY-2
L0EC9: DJNZ L0EB2 ; back to COPY-1 for all lines.
JR L0EDA ; forward to COPY-END to switch off the printer
; motor and enable interrupts.
; Note. Nothing else is required.
; ------------------------------
; Pass printer buffer to printer
; ------------------------------
; This routine is used to copy 8 text lines from the printer buffer
; to the ZX Printer. These text lines are mapped linearly so HL does
; not need to be adjusted at the end of each line.
;; COPY-BUFF
L0ECD: DI ; disable interrupts
LD HL,$5B00 ; the base address of the Printer Buffer.
LD B,$08 ; set count to 8 lines of 32 bytes.
;; COPY-3
L0ED3: PUSH BC ; save counter.
CALL L0EF4 ; routine COPY-LINE outputs 32 bytes
POP BC ; restore counter.
DJNZ L0ED3 ; loop back to COPY-3 for all 8 lines.
; then stop motor and clear buffer.
; Note. the COPY command rejoins here, essentially to execute the next
; three instructions.
;; COPY-END
L0EDA: LD A,$04 ; output value 4 to port
OUT ($FB),A ; to stop the slowed printer motor.
EI ; enable interrupts.
; --------------------
; Clear Printer Buffer
; --------------------
; This routine clears an arbitrary 256 bytes of memory.
; Note. The routine seems designed to clear a buffer that follows the
; system variables.
; The routine should check a flag or HL address and simply return if COPY
; is in use.
; As a consequence of this omission the buffer will needlessly
; be cleared when COPY is used and the screen/printer position may be set to
; the start of the buffer and the line number to 0 (B)
; giving an 'Out of Screen' error.
; There seems to have been an unsuccessful attempt to circumvent the use
; of PR_CC_hi.
;; CLEAR-PRB
L0EDF: LD HL,$5B00 ; the location of the buffer.
LD (IY+$46),L ; update PR_CC_lo - set to zero - superfluous.
XOR A ; clear the accumulator.
LD B,A ; set count to 256 bytes.
;; PRB-BYTES
L0EE7: LD (HL),A ; set addressed location to zero.
INC HL ; address next byte - Note. not INC L.
DJNZ L0EE7 ; back to PRB-BYTES. repeat for 256 bytes.
RES 1,(IY+$30) ; set FLAGS2 - signal printer buffer is clear.
LD C,$21 ; set the column position .
JP L0DD9 ; exit via CL-SET and then PO-STORE.
; -----------------
; Copy line routine
; -----------------
; This routine is called from COPY and COPY-BUFF to output a line of
; 32 bytes to the ZX Printer.
; Output to port $FB -
; bit 7 set - activate stylus.
; bit 7 low - deactivate stylus.
; bit 2 set - stops printer.
; bit 2 reset - starts printer
; bit 1 set - slows printer.
; bit 1 reset - normal speed.
;; COPY-LINE
L0EF4: LD A,B ; fetch the counter 1-8 or 1-176
CP $03 ; is it 01 or 02 ?.
SBC A,A ; result is $FF if so else $00.
AND $02 ; result is 02 now else 00.
; bit 1 set slows the printer.
OUT ($FB),A ; slow the printer for the
; last two lines.
LD D,A ; save the mask to control the printer later.
;; COPY-L-1
L0EFD: CALL L1F54 ; call BREAK-KEY to read keyboard immediately.
JR C,L0F0C ; forward to COPY-L-2 if 'break' not pressed.
LD A,$04 ; else stop the
OUT ($FB),A ; printer motor.
EI ; enable interrupts.
CALL L0EDF ; call routine CLEAR-PRB.
; Note. should not be cleared if COPY in use.
;; REPORT-Dc
L0F0A: RST 08H ; ERROR-1
DEFB $0C ; Error Report: BREAK - CONT repeats
;; COPY-L-2
L0F0C: IN A,($FB) ; test now to see if
ADD A,A ; a printer is attached.
RET M ; return if not - but continue with parent
; command.
JR NC,L0EFD ; back to COPY-L-1 if stylus of printer not
; in position.
LD C,$20 ; set count to 32 bytes.
;; COPY-L-3
L0F14: LD E,(HL) ; fetch a byte from line.
INC HL ; address next location. Note. not INC L.
LD B,$08 ; count the bits.
;; COPY-L-4
L0F18: RL D ; prepare mask to receive bit.
RL E ; rotate leftmost print bit to carry
RR D ; and back to bit 7 of D restoring bit 1
;; COPY-L-5
L0F1E: IN A,($FB) ; read the port.
RRA ; bit 0 to carry.
JR NC,L0F1E ; back to COPY-L-5 if stylus not in position.
LD A,D ; transfer command bits to A.
OUT ($FB),A ; and output to port.
DJNZ L0F18 ; loop back to COPY-L-4 for all 8 bits.
DEC C ; decrease the byte count.
JR NZ,L0F14 ; back to COPY-L-3 until 256 bits done.
RET ; return to calling routine COPY/COPY-BUFF.
; ----------------------------------
; Editor routine for BASIC and INPUT
; ----------------------------------
; The editor is called to prepare or edit a BASIC line.
; It is also called from INPUT to input a numeric or string expression.
; The behaviour and options are quite different in the various modes
; and distinguished by bit 5 of FLAGX.
;
; This is a compact and highly versatile routine.
;; EDITOR
L0F2C: LD HL,($5C3D) ; fetch ERR_SP
PUSH HL ; save on stack
;; ED-AGAIN
L0F30: LD HL,L107F ; address: ED-ERROR
PUSH HL ; save address on stack and
LD ($5C3D),SP ; make ERR_SP point to it.
; Note. While in editing/input mode should an error occur then RST 08 will
; update X_PTR to the location reached by CH_ADD and jump to ED-ERROR
; where the error will be cancelled and the loop begin again from ED-AGAIN
; above. The position of the error will be apparent when the lower screen is
; reprinted. If no error then the re-iteration is to ED-LOOP below when
; input is arriving from the keyboard.
;; ED-LOOP
L0F38: CALL L15D4 ; routine WAIT-KEY gets key possibly
; changing the mode.
PUSH AF ; save key.
LD D,$00 ; and give a short click based
LD E,(IY-$01) ; on PIP value for duration.
LD HL,$00C8 ; and pitch.
CALL L03B5 ; routine BEEPER gives click - effective
; with rubber keyboard.
POP AF ; get saved key value.
LD HL,L0F38 ; address: ED-LOOP is loaded to HL.
PUSH HL ; and pushed onto stack.
; At this point there is a looping return address on the stack, an error
; handler and an input stream set up to supply characters.
; The character that has been received can now be processed.
CP $18 ; range 24 to 255 ?
JR NC,L0F81 ; forward to ADD-CHAR if so.
CP $07 ; lower than 7 ?
JR C,L0F81 ; forward to ADD-CHAR also.
; Note. This is a 'bug' and chr$ 6, the comma
; control character, should have had an
; entry in the ED-KEYS table.
; Steven Vickers, 1984, Pitman.
CP $10 ; less than 16 ?
JR C,L0F92 ; forward to ED-KEYS if editing control
; range 7 to 15 dealt with by a table
LD BC,$0002 ; prepare for ink/paper etc.
LD D,A ; save character in D
CP $16 ; is it ink/paper/bright etc. ?
JR C,L0F6C ; forward to ED-CONTR if so
; leaves 22d AT and 23d TAB
; which can't be entered via KEY-INPUT.
; so this code is never normally executed
; when the keyboard is used for input.
INC BC ; if it was AT/TAB - 3 locations required
BIT 7,(IY+$37) ; test FLAGX - Is this INPUT LINE ?
JP Z,L101E ; jump to ED-IGNORE if not, else
CALL L15D4 ; routine WAIT-KEY - input address is KEY-NEXT
; but is reset to KEY-INPUT
LD E,A ; save first in E
;; ED-CONTR
L0F6C: CALL L15D4 ; routine WAIT-KEY for control.
; input address will be key-next.
PUSH DE ; saved code/parameters
LD HL,($5C5B) ; fetch address of keyboard cursor from K_CUR
RES 0,(IY+$07) ; set MODE to 'L'
CALL L1655 ; routine MAKE-ROOM makes 2/3 spaces at cursor
POP BC ; restore code/parameters
INC HL ; address first location
LD (HL),B ; place code (ink etc.)
INC HL ; address next
LD (HL),C ; place possible parameter. If only one
; then DE points to this location also.
JR L0F8B ; forward to ADD-CH-1
; ------------------------
; Add code to current line
; ------------------------
; this is the branch used to add normal non-control characters
; with ED-LOOP as the stacked return address.
; it is also the OUTPUT service routine for system channel 'R'.
;; ADD-CHAR
L0F81: RES 0,(IY+$07) ; set MODE to 'L'
X0F85: LD HL,($5C5B) ; fetch address of keyboard cursor from K_CUR
CALL L1652 ; routine ONE-SPACE creates one space.
; either a continuation of above or from ED-CONTR with ED-LOOP on stack.
;; ADD-CH-1
L0F8B: LD (DE),A ; load current character to last new location.
INC DE ; address next
LD ($5C5B),DE ; and update K_CUR system variable.
RET ; return - either a simple return
; from ADD-CHAR or to ED-LOOP on stack.
; ---
; a branch of the editing loop to deal with control characters
; using a look-up table.
;; ED-KEYS
L0F92: LD E,A ; character to E.
LD D,$00 ; prepare to add.
LD HL,L0FA0 - 7 ; base address of editing keys table. $0F99
ADD HL,DE ; add E
LD E,(HL) ; fetch offset to E
ADD HL,DE ; add offset for address of handling routine.
PUSH HL ; push the address on machine stack.
LD HL,($5C5B) ; load address of cursor from K_CUR.
RET ; Make an indirect jump forward to routine.
; ------------------
; Editing keys table
; ------------------
; For each code in the range $07 to $0F this table contains a
; single offset byte to the routine that services that code.
; Note. for what was intended there should also have been an
; entry for chr$ 6 with offset to ed-symbol.
;; ed-keys-t
L0FA0: DEFB L0FA9 - $ ; 07d offset $09 to Address: ED-EDIT
DEFB L1007 - $ ; 08d offset $66 to Address: ED-LEFT
DEFB L100C - $ ; 09d offset $6A to Address: ED-RIGHT
DEFB L0FF3 - $ ; 10d offset $50 to Address: ED-DOWN
DEFB L1059 - $ ; 11d offset $B5 to Address: ED-UP
DEFB L1015 - $ ; 12d offset $70 to Address: ED-DELETE
DEFB L1024 - $ ; 13d offset $7E to Address: ED-ENTER
DEFB L1076 - $ ; 14d offset $CF to Address: ED-SYMBOL
DEFB L107C - $ ; 15d offset $D4 to Address: ED-GRAPH
; ---------------
; Handle EDIT key
; ---------------
; The user has pressed SHIFT 1 to bring edit line down to bottom of screen.
; Alternatively the user wishes to clear the input buffer and start again.
; Alternatively ...
;; ED-EDIT
L0FA9: LD HL,($5C49) ; fetch E_PPC the last line number entered.
; Note. may not exist and may follow program.
BIT 5,(IY+$37) ; test FLAGX - input mode ?
JP NZ,L1097 ; jump forward to CLEAR-SP if not in editor.
CALL L196E ; routine LINE-ADDR to find address of line
; or following line if it doesn't exist.
CALL L1695 ; routine LINE-NO will get line number from
; address or previous line if at end-marker.
LD A,D ; if there is no program then DE will
OR E ; contain zero so test for this.
JP Z,L1097 ; jump to CLEAR-SP if so.
; Note. at this point we have a validated line number, not just an
; approximation and it would be best to update E_PPC with the true
; cursor line value which would enable the line cursor to be suppressed
; in all situations - see shortly.
PUSH HL ; save address of line.
INC HL ; address low byte of length.
LD C,(HL) ; transfer to C
INC HL ; next to high byte
LD B,(HL) ; transfer to B.
LD HL,$000A ; an overhead of ten bytes
ADD HL,BC ; is added to length.
LD B,H ; transfer adjusted value
LD C,L ; to BC register.
CALL L1F05 ; routine TEST-ROOM checks free memory.
CALL L1097 ; routine CLEAR-SP clears editing area.
LD HL,($5C51) ; address CURCHL
EX (SP),HL ; swap with line address on stack
PUSH HL ; save line address underneath
LD A,$FF ; select system channel 'R'
CALL L1601 ; routine CHAN-OPEN opens it
POP HL ; drop line address
DEC HL ; make it point to first byte of line num.
DEC (IY+$0F) ; decrease E_PPC_lo to suppress line cursor.
; Note. ineffective when E_PPC is one
; greater than last line of program perhaps
; as a result of a delete.
; credit. Paul Harrison 1982.
CALL L1855 ; routine OUT-LINE outputs the BASIC line
; to the editing area.
INC (IY+$0F) ; restore E_PPC_lo to the previous value.
LD HL,($5C59) ; address E_LINE in editing area.
INC HL ; advance
INC HL ; past space
INC HL ; and digit characters
INC HL ; of line number.
LD ($5C5B),HL ; update K_CUR to address start of BASIC.
POP HL ; restore the address of CURCHL.
CALL L1615 ; routine CHAN-FLAG sets flags for it.
RET ; RETURN to ED-LOOP.
; -------------------
; Cursor down editing
; -------------------
; The BASIC lines are displayed at the top of the screen and the user
; wishes to move the cursor down one line in edit mode.
; With INPUT LINE, this key must be used instead of entering STOP.
;; ED-DOWN
L0FF3: BIT 5,(IY+$37) ; test FLAGX - Input Mode ?
JR NZ,L1001 ; skip to ED-STOP if so
LD HL,$5C49 ; address E_PPC - 'current line'
CALL L190F ; routine LN-FETCH fetches number of next
; line or same if at end of program.
JR L106E ; forward to ED-LIST to produce an
; automatic listing.
; ---
;; ED-STOP
L1001: LD (IY+$00),$10 ; set ERR_NR to 'STOP in INPUT' code
JR L1024 ; forward to ED-ENTER to produce error.
; -------------------
; Cursor left editing
; -------------------
; This acts on the cursor in the lower section of the screen in both
; editing and input mode.
;; ED-LEFT
L1007: CALL L1031 ; routine ED-EDGE moves left if possible
JR L1011 ; forward to ED-CUR to update K-CUR
; and return to ED-LOOP.
; --------------------
; Cursor right editing
; --------------------
; This acts on the cursor in the lower screen in both editing and input
; mode and moves it to the right.
;; ED-RIGHT
L100C: LD A,(HL) ; fetch addressed character.
CP $0D ; is it carriage return ?
RET Z ; return if so to ED-LOOP
INC HL ; address next character
;; ED-CUR
L1011: LD ($5C5B),HL ; update K_CUR system variable
RET ; return to ED-LOOP
; --------------
; DELETE editing
; --------------
; This acts on the lower screen and deletes the character to left of
; cursor. If control characters are present these are deleted first
; leaving the naked parameter (0-7) which appears as a '?' except in the
; case of chr$ 6 which is the comma control character. It is not mandatory
; to delete these second characters.
;; ED-DELETE
L1015: CALL L1031 ; routine ED-EDGE moves cursor to left.
LD BC,$0001 ; of character to be deleted.
JP L19E8 ; to RECLAIM-2 reclaim the character.
; ------------------------------------------
; Ignore next 2 codes from key-input routine
; ------------------------------------------
; Since AT and TAB cannot be entered this point is never reached
; from the keyboard. If inputting from a tape device or network then
; the control and two following characters are ignored and processing
; continues as if a carriage return had been received.
; Here, perhaps, another Spectrum has said print #15; AT 0,0; "This is yellow"
; and this one is interpreting input #15; a$.
;; ED-IGNORE
L101E: CALL L15D4 ; routine WAIT-KEY to ignore keystroke.
CALL L15D4 ; routine WAIT-KEY to ignore next key.
; -------------
; Enter/newline
; -------------
; The enter key has been pressed to have BASIC line or input accepted.
;; ED-ENTER
L1024: POP HL ; discard address ED-LOOP
POP HL ; drop address ED-ERROR
;; ED-END
L1026: POP HL ; the previous value of ERR_SP
LD ($5C3D),HL ; is restored to ERR_SP system variable
BIT 7,(IY+$00) ; is ERR_NR $FF (= 'OK') ?
RET NZ ; return if so
LD SP,HL ; else put error routine on stack
RET ; and make an indirect jump to it.
; -----------------------------
; Move cursor left when editing
; -----------------------------
; This routine moves the cursor left. The complication is that it must
; not position the cursor between control codes and their parameters.
; It is further complicated in that it deals with TAB and AT characters
; which are never present from the keyboard.
; The method is to advance from the beginning of the line each time,
; jumping one, two, or three characters as necessary saving the original
; position at each jump in DE. Once it arrives at the cursor then the next
; legitimate leftmost position is in DE.
;; ED-EDGE
L1031: SCF ; carry flag must be set to call the nested
CALL L1195 ; subroutine SET-DE.
; if input then DE=WORKSP
; if editing then DE=E_LINE
SBC HL,DE ; subtract address from start of line
ADD HL,DE ; and add back.
INC HL ; adjust for carry.
POP BC ; drop return address
RET C ; return to ED-LOOP if already at left
; of line.
PUSH BC ; resave return address - ED-LOOP.
LD B,H ; transfer HL - cursor address
LD C,L ; to BC register pair.
; at this point DE addresses start of line.
;; ED-EDGE-1
L103E: LD H,D ; transfer DE - leftmost pointer
LD L,E ; to HL
INC HL ; address next leftmost character to
; advance position each time.
LD A,(DE) ; pick up previous in A
AND $F0 ; lose the low bits
CP $10 ; is it INK to TAB $10-$1F ?
; that is, is it followed by a parameter ?
JR NZ,L1051 ; to ED-EDGE-2 if not
; HL has been incremented once
INC HL ; address next as at least one parameter.
; in fact since 'tab' and 'at' cannot be entered the next section seems
; superfluous.
; The test will always fail and the jump to ED-EDGE-2 will be taken.
LD A,(DE) ; reload leftmost character
SUB $17 ; decimal 23 ('tab')
ADC A,$00 ; will be 0 for 'tab' and 'at'.
JR NZ,L1051 ; forward to ED-EDGE-2 if not
; HL has been incremented twice
INC HL ; increment a third time for 'at'/'tab'
;; ED-EDGE-2
L1051: AND A ; prepare for true subtraction
SBC HL,BC ; subtract cursor address from pointer
ADD HL,BC ; and add back
; Note when HL matches the cursor position BC,
; there is no carry and the previous
; position is in DE.
EX DE,HL ; transfer result to DE if looping again.
; transfer DE to HL to be used as K-CUR
; if exiting loop.
JR C,L103E ; back to ED-EDGE-1 if cursor not matched.
RET ; return.
; -----------------
; Cursor up editing
; -----------------
; The main screen displays part of the BASIC program and the user wishes
; to move up one line scrolling if necessary.
; This has no alternative use in input mode.
;; ED-UP
L1059: BIT 5,(IY+$37) ; test FLAGX - input mode ?
RET NZ ; return if not in editor - to ED-LOOP.
LD HL,($5C49) ; get current line from E_PPC
CALL L196E ; routine LINE-ADDR gets address
EX DE,HL ; and previous in DE
CALL L1695 ; routine LINE-NO gets prev line number
LD HL,$5C4A ; set HL to E_PPC_hi as next routine stores
; top first.
CALL L191C ; routine LN-STORE loads DE value to HL
; high byte first - E_PPC_lo takes E
; this branch is also taken from ed-down.
;; ED-LIST
L106E: CALL L1795 ; routine AUTO-LIST lists to upper screen
; including adjusted current line.
LD A,$00 ; select lower screen again
JP L1601 ; exit via CHAN-OPEN to ED-LOOP
; --------------------------------
; Use of symbol and graphics codes
; --------------------------------
; These will not be encountered with the keyboard but would be handled
; otherwise as follows.
; As noted earlier, Vickers says there should have been an entry in
; the KEYS table for chr$ 6 which also pointed here.
; If, for simplicity, two Spectrums were both using #15 as a bi-directional
; channel connected to each other:-
; then when the other Spectrum has said PRINT #15; x, y
; input #15; i ; j would treat the comma control as a newline and the
; control would skip to input j.
; You can get round the missing chr$ 6 handler by sending multiple print
; items separated by a newline '.
; chr$14 would have the same functionality.
; This is chr$ 14.
;; ED-SYMBOL
L1076: BIT 7,(IY+$37) ; test FLAGX - is this INPUT LINE ?
JR Z,L1024 ; back to ED-ENTER if not to treat as if
; enter had been pressed.
; else continue and add code to buffer.
; Next is chr$ 15
; Note that ADD-CHAR precedes the table so we can't offset to it directly.
;; ED-GRAPH
L107C: JP L0F81 ; jump back to ADD-CHAR
; --------------------
; Editor error routine
; --------------------
; If an error occurs while editing, or inputting, then ERR_SP
; points to the stack location holding address ED_ERROR.
;; ED-ERROR
L107F: BIT 4,(IY+$30) ; test FLAGS2 - is K channel in use ?
JR Z,L1026 ; back to ED-END if not.
; but as long as we're editing lines or inputting from the keyboard, then
; we've run out of memory so give a short rasp.
LD (IY+$00),$FF ; reset ERR_NR to 'OK'.
LD D,$00 ; prepare for beeper.
LD E,(IY-$02) ; use RASP value.
LD HL,$1A90 ; set the pitch - or tone period.
CALL L03B5 ; routine BEEPER emits a warning rasp.
JP L0F30 ; to ED-AGAIN to re-stack address of
; this routine and make ERR_SP point to it.
; ---------------------
; Clear edit/work space
; ---------------------
; The editing area or workspace is cleared depending on context.
; This is called from ED-EDIT to clear workspace if edit key is
; used during input, to clear editing area if no program exists
; and to clear editing area prior to copying the edit line to it.
; It is also used by the error routine to clear the respective
; area depending on FLAGX.
;; CLEAR-SP
L1097: PUSH HL ; preserve HL
CALL L1190 ; routine SET-HL
; if in edit HL = WORKSP-1, DE = E_LINE
; if in input HL = STKBOT, DE = WORKSP
DEC HL ; adjust
CALL L19E5 ; routine RECLAIM-1 reclaims space
LD ($5C5B),HL ; set K_CUR to start of empty area
LD (IY+$07),$00 ; set MODE to 'KLC'
POP HL ; restore HL.
RET ; return.
; ----------------------------
; THE 'KEYBOARD INPUT' ROUTINE
; ----------------------------
; This is the service routine for the input stream of the keyboard channel 'K'.
;; KEY-INPUT
L10A8: BIT 3,(IY+$02) ; test TV_FLAG - has a key been pressed in
; editor ?
CALL NZ,L111D ; routine ED-COPY, if so, to reprint the lower
; screen at every keystroke/mode change.
AND A ; clear carry flag - required exit condition.
BIT 5,(IY+$01) ; test FLAGS - has a new key been pressed ?
RET Z ; return if not. >>
LD A,($5C08) ; system variable LASTK will hold last key -
; from the interrupt routine.
RES 5,(IY+$01) ; update FLAGS - reset the new key flag.
PUSH AF ; save the input character.
BIT 5,(IY+$02) ; test TV_FLAG - clear lower screen ?
CALL NZ,L0D6E ; routine CLS-LOWER if so.
POP AF ; restore the character code.
CP $20 ; if space or higher then
JR NC,L111B ; forward to KEY-DONE2 and return with carry
; set to signal key-found.
CP $10 ; with 16d INK and higher skip
JR NC,L10FA ; forward to KEY-CONTR.
CP $06 ; for 6 - 15d
JR NC,L10DB ; skip forward to KEY-M-CL to handle Modes
; and CapsLock.
; that only leaves 0-5, the flash bright inverse switches.
LD B,A ; save character in B
AND $01 ; isolate the embedded parameter (0/1).
LD C,A ; and store in C
LD A,B ; re-fetch copy (0-5)
RRA ; halve it 0, 1 or 2.
ADD A,$12 ; add 18d gives 'flash', 'bright'
; and 'inverse'.
JR L1105 ; forward to KEY-DATA with the
; parameter (0/1) in C.
; ---
; Now separate capslock 06 from modes 7-15.
;; KEY-M-CL
L10DB: JR NZ,L10E6 ; forward to KEY-MODE if not 06 (capslock)
LD HL,$5C6A ; point to FLAGS2
LD A,$08 ; value 00001000
XOR (HL) ; toggle BIT 3 of FLAGS2 the capslock bit
LD (HL),A ; and store result in FLAGS2 again.
JR L10F4 ; forward to KEY-FLAG to signal no-key.
; ---
;; KEY-MODE
L10E6: CP $0E ; compare with chr 14d
RET C ; return with carry set "key found" for
; codes 7 - 13d leaving 14d and 15d
; which are converted to mode codes.
SUB $0D ; subtract 13d leaving 1 and 2
; 1 is 'E' mode, 2 is 'G' mode.
LD HL,$5C41 ; address the MODE system variable.
CP (HL) ; compare with existing value before
LD (HL),A ; inserting the new value.
JR NZ,L10F4 ; forward to KEY-FLAG if it has changed.
LD (HL),$00 ; else make MODE zero - KLC mode
; Note. while in Extended/Graphics mode,
; the Extended Mode/Graphics key is pressed
; again to get out.
;; KEY-FLAG
L10F4: SET 3,(IY+$02) ; update TV_FLAG - show key state has changed
CP A ; clear carry and reset zero flags -
; no actual key returned.
RET ; make the return.
; ---
; now deal with colour controls - 16-23 ink, 24-31 paper
;; KEY-CONTR
L10FA: LD B,A ; make a copy of character.
AND $07 ; mask to leave bits 0-7
LD C,A ; and store in C.
LD A,$10 ; initialize to 16d - INK.
BIT 3,B ; was it paper ?
JR NZ,L1105 ; forward to KEY-DATA with INK 16d and
; colour in C.
INC A ; else change from INK to PAPER (17d) if so.
;; KEY-DATA
L1105: LD (IY-$2D),C ; put the colour (0-7)/state(0/1) in KDATA
LD DE,L110D ; address: KEY-NEXT will be next input stream
JR L1113 ; forward to KEY-CHAN to change it ...
; ---
; ... so that INPUT_AD directs control to here at next call to WAIT-KEY
;; KEY-NEXT
L110D: LD A,($5C0D) ; pick up the parameter stored in KDATA.
LD DE,L10A8 ; address: KEY-INPUT will be next input stream
; continue to restore default channel and
; make a return with the control code.
;; KEY-CHAN
L1113: LD HL,($5C4F) ; address start of CHANNELS area using CHANS
; system variable.
; Note. One might have expected CURCHL to
; have been used.
INC HL ; step over the
INC HL ; output address
LD (HL),E ; and update the input
INC HL ; routine address for
LD (HL),D ; the next call to WAIT-KEY.
;; KEY-DONE2
L111B: SCF ; set carry flag to show a key has been found
RET ; and return.
; --------------------
; Lower screen copying
; --------------------
; This subroutine is called whenever the line in the editing area or
; input workspace is required to be printed to the lower screen.
; It is by calling this routine after any change that the cursor, for
; instance, appears to move to the left.
; Remember the edit line will contain characters and tokens
; e.g. "1000 LET a=1" is 8 characters.
;; ED-COPY
L111D: CALL L0D4D ; routine TEMPS sets temporary attributes.
RES 3,(IY+$02) ; update TV_FLAG - signal no change in mode
RES 5,(IY+$02) ; update TV_FLAG - signal don't clear lower
; screen.
LD HL,($5C8A) ; fetch SPOSNL
PUSH HL ; and save on stack.
LD HL,($5C3D) ; fetch ERR_SP
PUSH HL ; and save also
LD HL,L1167 ; address: ED-FULL
PUSH HL ; is pushed as the error routine
LD ($5C3D),SP ; and ERR_SP made to point to it.
LD HL,($5C82) ; fetch ECHO_E
PUSH HL ; and push also
SCF ; set carry flag to control SET-DE
CALL L1195 ; call routine SET-DE
; if in input DE = WORKSP
; if in edit DE = E_LINE
EX DE,HL ; start address to HL
CALL L187D ; routine OUT-LINE2 outputs entire line up to
; carriage return including initial
; characterized line number when present.
EX DE,HL ; transfer new address to DE
CALL L18E1 ; routine OUT-CURS considers a
; terminating cursor.
LD HL,($5C8A) ; fetch updated SPOSNL
EX (SP),HL ; exchange with ECHO_E on stack
EX DE,HL ; transfer ECHO_E to DE
CALL L0D4D ; routine TEMPS to re-set attributes
; if altered.
; the lower screen was not cleared, at the outset, so if deleting then old
; text from a previous print may follow this line and requires blanking.
;; ED-BLANK
L1150: LD A,($5C8B) ; fetch SPOSNL_hi is current line
SUB D ; compare with old
JR C,L117C ; forward to ED-C-DONE if no blanking
JR NZ,L115E ; forward to ED-SPACES if line has changed
LD A,E ; old column to A
SUB (IY+$50) ; subtract new in SPOSNL_lo
JR NC,L117C ; forward to ED-C-DONE if no backfilling.
;; ED-SPACES
L115E: LD A,$20 ; prepare a space.
PUSH DE ; save old line/column.
CALL L09F4 ; routine PRINT-OUT prints a space over
; any text from previous print.
; Note. Since the blanking only occurs when
; using $09F4 to print to the lower screen,
; there is no need to vector via a RST 10
; and we can use this alternate set.
POP DE ; restore the old line column.
JR L1150 ; back to ED-BLANK until all old text blanked.
; -------------------------------
; THE 'EDITOR-FULL' ERROR ROUTINE
; -------------------------------
; This is the error routine addressed by ERR_SP. This is not for the out of
; memory situation as we're just printing. The pitch and duration are exactly
; the same as used by ED-ERROR from which this has been augmented. The
; situation is that the lower screen is full and a rasp is given to suggest
; that this is perhaps not the best idea you've had that day.
;; ED-FULL
L1167: LD D,$00 ; prepare to moan.
LD E,(IY-$02) ; fetch RASP value.
LD HL,$1A90 ; set pitch or tone period.
CALL L03B5 ; routine BEEPER.
LD (IY+$00),$FF ; clear ERR_NR.
LD DE,($5C8A) ; fetch SPOSNL.
JR L117E ; forward to ED-C-END
; -------
; the exit point from line printing continues here.
;; ED-C-DONE
L117C: POP DE ; fetch new line/column.
POP HL ; fetch the error address.
; the error path rejoins here.
;; ED-C-END
L117E: POP HL ; restore the old value of ERR_SP.
LD ($5C3D),HL ; update the system variable ERR_SP
POP BC ; old value of SPOSN_L
PUSH DE ; save new value
CALL L0DD9 ; routine CL-SET and PO-STORE
; update ECHO_E and SPOSN_L from BC
POP HL ; restore new value
LD ($5C82),HL ; and overwrite ECHO_E
LD (IY+$26),$00 ; make error pointer X_PTR_hi out of bounds
RET ; return
; -----------------------------------------------
; Point to first and last locations of work space
; -----------------------------------------------
; These two nested routines ensure that the appropriate pointers are
; selected for the editing area or workspace. The routines that call
; these routines are designed to work on either area.
; this routine is called once
;; SET-HL
L1190: LD HL,($5C61) ; fetch WORKSP to HL.
DEC HL ; point to last location of editing area.
AND A ; clear carry to limit exit points to first
; or last.
; this routine is called with carry set and exits at a conditional return.
;; SET-DE
L1195: LD DE,($5C59) ; fetch E_LINE to DE
BIT 5,(IY+$37) ; test FLAGX - Input Mode ?
RET Z ; return now if in editing mode
LD DE,($5C61) ; fetch WORKSP to DE
RET C ; return if carry set ( entry = set-de)
LD HL,($5C63) ; fetch STKBOT to HL as well
RET ; and return (entry = set-hl (in input))
; -----------------------------------
; THE 'REMOVE FLOATING POINT' ROUTINE
; -----------------------------------
; When a BASIC LINE or the INPUT BUFFER is parsed any numbers will have
; an invisible chr 14d inserted after them and the 5-byte integer or
; floating point form inserted after that. Similar invisible value holders
; are also created after the numeric and string variables in a DEF FN list.
; This routine removes these 'compiled' numbers from the edit line or
; input workspace.
;; REMOVE-FP
L11A7: LD A,(HL) ; fetch character
CP $0E ; is it the CHR$ 14 number marker ?
LD BC,$0006 ; prepare to strip six bytes
CALL Z,L19E8 ; routine RECLAIM-2 reclaims bytes if CHR$ 14.
LD A,(HL) ; reload next (or same) character
INC HL ; and advance address
CP $0D ; end of line or input buffer ?
JR NZ,L11A7 ; back to REMOVE-FP until entire line done.
RET ; return.
; *********************************
; ** Part 6. EXECUTIVE ROUTINES **
; *********************************
; The memory.
;
; +---------+-----------+------------+--------------+-------------+--
; | BASIC | Display | Attributes | ZX Printer | System |
; | ROM | File | File | Buffer | Variables |
; +---------+-----------+------------+--------------+-------------+--
; ^ ^ ^ ^ ^ ^
; $0000 $4000 $5800 $5B00 $5C00 $5CB6 = CHANS
;
;
; --+----------+---+---------+-----------+---+------------+--+---+--
; | Channel |$80| BASIC | Variables |$80| Edit Line |NL|$80|
; | Info | | Program | Area | | or Command | | |
; --+----------+---+---------+-----------+---+------------+--+---+--
; ^ ^ ^ ^ ^
; CHANS PROG VARS E_LINE WORKSP
;
;
; ---5--> <---2--- <--3---
; --+-------+--+------------+-------+-------+---------+-------+-+---+------+
; | INPUT |NL| Temporary | Calc. | Spare | Machine | GOSUB |?|$3E| UDGs |
; | data | | Work Space | Stack | | Stack | Stack | | | |
; --+-------+--+------------+-------+-------+---------+-------+-+---+------+
; ^ ^ ^ ^ ^ ^ ^
; WORKSP STKBOT STKEND sp RAMTOP UDG P_RAMT
;
; -----------------
; THE 'NEW' COMMAND
; -----------------
; The NEW command is about to set all RAM below RAMTOP to zero and then
; re-initialize the system. All RAM above RAMTOP should, and will be,
; preserved.
; There is nowhere to store values in RAM or on the stack which becomes
; inoperable. Similarly PUSH and CALL instructions cannot be used to store
; values or section common code. The alternate register set is the only place
; available to store 3 persistent 16-bit system variables.
;; NEW
L11B7: DI ; Disable Interrupts - machine stack will be
; cleared.
LD A,$FF ; Flag coming from NEW.
LD DE,($5CB2) ; Fetch RAMTOP as top value.
EXX ; Switch in alternate set.
LD BC,($5CB4) ; Fetch P-RAMT differs on 16K/48K machines.
LD DE,($5C38) ; Fetch RASP/PIP.
LD HL,($5C7B) ; Fetch UDG differs on 16K/48K machines.
EXX ; Switch back to main set and continue into...
; ----------------------
; THE 'START-NEW' BRANCH
; ----------------------
; This branch is taken from above and from RST 00h.
; The common code tests RAM and sets it to zero re-initializing all the
; non-zero system variables and channel information. The A register flags
; if coming from START or NEW.
;; START-NEW
L11CB: LD B,A ; Save the flag to control later branching.
LD A,$07 ; Select a white border
OUT ($FE),A ; and set it now by writing to a port.
LD A,$3F ; Load the accumulator with last page in ROM.
LD I,A ; Set the I register - this remains constant
; and can't be in the range $40 - $7F as 'snow'
; appears on the screen.
NOP ; These seem unnecessary.
NOP ;
NOP ;
NOP ;
NOP ;
NOP ;
; -----------------------
; THE 'RAM CHECK' SECTION
; -----------------------
; Typically, a Spectrum will have 16K or 48K of RAM and this code will test
; it all till it finds an unpopulated location or, less likely, a faulty
; location. Usually it stops when it reaches the top $FFFF, or in the case
; of NEW the supplied top value. The entire screen turns black with
; sometimes red stripes on black paper just visible.
;; ram-check
L11DA: LD H,D ; Transfer the top value to the HL register
LD L,E ; pair.
;; RAM-FILL
L11DC: LD (HL),$02 ; Load memory with $02 - red ink on black paper.
DEC HL ; Decrement memory address.
CP H ; Have we reached ROM - $3F ?
JR NZ,L11DC ; Back to RAM-FILL if not.
;; RAM-READ
L11E2: AND A ; Clear carry - prepare to subtract.
SBC HL,DE ; subtract and add back setting
ADD HL,DE ; carry when back at start.
INC HL ; and increment for next iteration.
JR NC,L11EF ; forward to RAM-DONE if we've got back to
; starting point with no errors.
DEC (HL) ; decrement to 1.
JR Z,L11EF ; forward to RAM-DONE if faulty.
DEC (HL) ; decrement to zero.
JR Z,L11E2 ; back to RAM-READ if zero flag was set.
;; RAM-DONE
L11EF: DEC HL ; step back to last valid location.
EXX ; regardless of state, set up possibly
; stored system variables in case from NEW.
LD ($5CB4),BC ; insert P-RAMT.
LD ($5C38),DE ; insert RASP/PIP.
LD ($5C7B),HL ; insert UDG.
EXX ; switch in main set.
INC B ; now test if we arrived here from NEW.
JR Z,L1219 ; forward to RAM-SET if we did.
; This section applies to START only.
LD ($5CB4),HL ; set P-RAMT to the highest working RAM
; address.
LD DE,$3EAF ; address of last byte of 'U' bitmap in ROM.
LD BC,$00A8 ; there are 21 user defined graphics.
EX DE,HL ; switch pointers and make the UDGs a
LDDR ; copy of the standard characters A - U.
EX DE,HL ; switch the pointer to HL.
INC HL ; update to start of 'A' in RAM.
LD ($5C7B),HL ; make UDG system variable address the first
; bitmap.
DEC HL ; point at RAMTOP again.
LD BC,$0040 ; set the values of
LD ($5C38),BC ; the PIP and RASP system variables.
; The NEW command path rejoins here.
;; RAM-SET
L1219: LD ($5CB2),HL ; set system variable RAMTOP to HL.
;
; Note. this entry point is a disabled Warm Restart that was almost certainly
; once pointed to by the System Variable NMIADD. It would be essential that
; any NMI Handler would perform the tasks from here to the EI instruction
; below.
;; NMI_VECT
L121C:
LD HL,$3C00 ; a strange place to set the pointer to the
LD ($5C36),HL ; character set, CHARS - as no printing yet.
LD HL,($5CB2) ; fetch RAMTOP to HL again as we've lost it.
LD (HL),$3E ; top of user ram holds GOSUB end marker
; an impossible line number - see RETURN.
; no significance in the number $3E. It has
; been traditional since the ZX80.
DEC HL ; followed by empty byte (not important).
LD SP,HL ; set up the machine stack pointer.
DEC HL ;
DEC HL ;
LD ($5C3D),HL ; ERR_SP is where the error pointer is
; at moment empty - will take address MAIN-4
; at the call preceding that address,
; although interrupts and calls will make use
; of this location in meantime.
IM 1 ; select interrupt mode 1.
LD IY,$5C3A ; set IY to ERR_NR. IY can reach all standard
; system variables but shadow ROM system
; variables will be mostly out of range.
EI ; enable interrupts now that we have a stack.
; If, as suggested above, the NMI service routine pointed to this section of
; code then a decision would have to be made at this point to jump forward,
; in a Warm Restart scenario, to produce a report code, leaving any program
; intact.
LD HL,$5CB6 ; The address of the channels - initially
; following system variables.
LD ($5C4F),HL ; Set the CHANS system variable.
LD DE,L15AF ; Address: init-chan in ROM.
LD BC,$0015 ; There are 21 bytes of initial data in ROM.
EX DE,HL ; swap the pointers.
LDIR ; Copy the bytes to RAM.
EX DE,HL ; Swap pointers. HL points to program area.
DEC HL ; Decrement address.
LD ($5C57),HL ; Set DATADD to location before program area.
INC HL ; Increment again.
LD ($5C53),HL ; Set PROG the location where BASIC starts.
LD ($5C4B),HL ; Set VARS to same location with a
LD (HL),$80 ; variables end-marker.
INC HL ; Advance address.
LD ($5C59),HL ; Set E_LINE, where the edit line
; will be created.
; Note. it is not strictly necessary to
; execute the next fifteen bytes of code
; as this will be done by the call to SET-MIN.
; --
LD (HL),$0D ; initially just has a carriage return
INC HL ; followed by
LD (HL),$80 ; an end-marker.
INC HL ; address the next location.
LD ($5C61),HL ; set WORKSP - empty workspace.
LD ($5C63),HL ; set STKBOT - bottom of the empty stack.
LD ($5C65),HL ; set STKEND to the end of the empty stack.
; --
LD A,$38 ; the colour system is set to white paper,
; black ink, no flash or bright.
LD ($5C8D),A ; set ATTR_P permanent colour attributes.
LD ($5C8F),A ; set ATTR_T temporary colour attributes.
LD ($5C48),A ; set BORDCR the border colour/lower screen
; attributes.
LD HL,$0523 ; The keyboard repeat and delay values are
LD ($5C09),HL ; loaded to REPDEL and REPPER.
DEC (IY-$3A) ; set KSTATE-0 to $FF - keyboard map available.
DEC (IY-$36) ; set KSTATE-4 to $FF - keyboard map available.
LD HL,L15C6 ; set source to ROM Address: init-strm
LD DE,$5C10 ; set destination to system variable STRMS-FD
LD BC,$000E ; copy the 14 bytes of initial 7 streams data
LDIR ; from ROM to RAM.
SET 1,(IY+$01) ; update FLAGS - signal printer in use.
CALL L0EDF ; call routine CLEAR-PRB to initialize system
; variables associated with printer.
; The buffer is clear.
LD (IY+$31),$02 ; set DF_SZ the lower screen display size to
; two lines
CALL L0D6B ; call routine CLS to set up system
; variables associated with screen and clear
; the screen and set attributes.
XOR A ; clear accumulator so that we can address
LD DE,L1539 - 1 ; the message table directly.
CALL L0C0A ; routine PO-MSG puts
; ' © 1982 Sinclair Research Ltd'
; at bottom of display.
SET 5,(IY+$02) ; update TV_FLAG - signal lower screen will
; require clearing.
JR L12A9 ; forward to MAIN-1
; -------------------------
; THE 'MAIN EXECUTION LOOP'
; -------------------------
;
;
;; MAIN-EXEC
L12A2: LD (IY+$31),$02 ; set DF_SZ lower screen display file size to
; two lines.
CALL L1795 ; routine AUTO-LIST
;; MAIN-1
L12A9: CALL L16B0 ; routine SET-MIN clears work areas.
;; MAIN-2
L12AC: LD A,$00 ; select channel 'K' the keyboard
CALL L1601 ; routine CHAN-OPEN opens it
CALL L0F2C ; routine EDITOR is called.
; Note the above routine is where the Spectrum
; waits for user-interaction. Perhaps the
; most common input at this stage
; is LOAD "".
CALL L1B17 ; routine LINE-SCAN scans the input.
BIT 7,(IY+$00) ; test ERR_NR - will be $FF if syntax is OK.
JR NZ,L12CF ; forward, if correct, to MAIN-3.
;
BIT 4,(IY+$30) ; test FLAGS2 - K channel in use ?
JR Z,L1303 ; forward to MAIN-4 if not.
;
LD HL,($5C59) ; an editing error so address E_LINE.
CALL L11A7 ; routine REMOVE-FP removes the hidden
; floating-point forms.
LD (IY+$00),$FF ; system variable ERR_NR is reset to 'OK'.
JR L12AC ; back to MAIN-2 to allow user to correct.
; ---
; the branch was here if syntax has passed test.
;; MAIN-3
L12CF: LD HL,($5C59) ; fetch the edit line address from E_LINE.
LD ($5C5D),HL ; system variable CH_ADD is set to first
; character of edit line.
; Note. the above two instructions are a little
; inadequate.
; They are repeated with a subtle difference
; at the start of the next subroutine and are
; therefore not required above.
CALL L19FB ; routine E-LINE-NO will fetch any line
; number to BC if this is a program line.
LD A,B ; test if the number of
OR C ; the line is non-zero.
JP NZ,L155D ; jump forward to MAIN-ADD if so to add the
; line to the BASIC program.
; Has the user just pressed the ENTER key ?
RST 18H ; GET-CHAR gets character addressed by CH_ADD.
CP $0D ; is it a carriage return ?
JR Z,L12A2 ; back to MAIN-EXEC if so for an automatic
; listing.
; this must be a direct command.
BIT 0,(IY+$30) ; test FLAGS2 - clear the main screen ?
CALL NZ,L0DAF ; routine CL-ALL, if so, e.g. after listing.
CALL L0D6E ; routine CLS-LOWER anyway.
LD A,$19 ; compute scroll count as 25 minus
SUB (IY+$4F) ; value of S_POSN_hi.
LD ($5C8C),A ; update SCR_CT system variable.
SET 7,(IY+$01) ; update FLAGS - signal running program.
LD (IY+$00),$FF ; set ERR_NR to 'OK'.
LD (IY+$0A),$01 ; set NSPPC to one for first statement.
CALL L1B8A ; call routine LINE-RUN to run the line.
; sysvar ERR_SP therefore addresses MAIN-4
; Examples of direct commands are RUN, CLS, LOAD "", PRINT USR 40000,
; LPRINT "A"; etc..
; If a user written machine-code program disables interrupts then it
; must enable them to pass the next step. We also jumped to here if the
; keyboard was not being used.
;; MAIN-4
L1303: HALT ; wait for interrupt the only routine that can
; set bit 5 of FLAGS.
RES 5,(IY+$01) ; update bit 5 of FLAGS - signal no new key.
BIT 1,(IY+$30) ; test FLAGS2 - is printer buffer clear ?
CALL NZ,L0ECD ; call routine COPY-BUFF if not.
; Note. the programmer has neglected
; to set bit 1 of FLAGS first.
LD A,($5C3A) ; fetch ERR_NR
INC A ; increment to give true code.
; Now deal with a runtime error as opposed to an editing error.
; However if the error code is now zero then the OK message will be printed.
;; MAIN-G
L1313: PUSH AF ; save the error number.
LD HL,$0000 ; prepare to clear some system variables.
LD (IY+$37),H ; clear all the bits of FLAGX.
LD (IY+$26),H ; blank X_PTR_hi to suppress error marker.
LD ($5C0B),HL ; blank DEFADD to signal that no defined
; function is currently being evaluated.
LD HL,$0001 ; explicit - inc hl would do.
LD ($5C16),HL ; ensure STRMS-00 is keyboard.
CALL L16B0 ; routine SET-MIN clears workspace etc.
RES 5,(IY+$37) ; update FLAGX - signal in EDIT not INPUT mode.
; Note. all the bits were reset earlier.
CALL L0D6E ; call routine CLS-LOWER.
SET 5,(IY+$02) ; update TV_FLAG - signal lower screen
; requires clearing.
POP AF ; bring back the true error number
LD B,A ; and make a copy in B.
CP $0A ; is it a print-ready digit ?
JR C,L133C ; forward to MAIN-5 if so.
ADD A,$07 ; add ASCII offset to letters.
;; MAIN-5
L133C: CALL L15EF ; call routine OUT-CODE to print the code.
LD A,$20 ; followed by a space.
RST 10H ; PRINT-A
LD A,B ; fetch stored report code.
LD DE,L1391 ; address: rpt-mesgs.
CALL L0C0A ; call routine PO-MSG to print the message.
X1349: XOR A ; clear accumulator to directly
LD DE,L1537 - 1 ; address the comma and space message.
CALL L0C0A ; routine PO-MSG prints ', ' although it would
; be more succinct to use RST $10.
LD BC,($5C45) ; fetch PPC the current line number.
CALL L1A1B ; routine OUT-NUM-1 will print that
LD A,$3A ; then a ':' character.
RST 10H ; PRINT-A
LD C,(IY+$0D) ; then SUBPPC for statement
LD B,$00 ; limited to 127
CALL L1A1B ; routine OUT-NUM-1 prints BC.
CALL L1097 ; routine CLEAR-SP clears editing area which
; probably contained 'RUN'.
LD A,($5C3A) ; fetch ERR_NR again
INC A ; test for no error originally $FF.
JR Z,L1386 ; forward to MAIN-9 if no error.
CP $09 ; is code Report 9 STOP ?
JR Z,L1373 ; forward to MAIN-6 if so
CP $15 ; is code Report L Break ?
JR NZ,L1376 ; forward to MAIN-7 if not
; Stop or Break was encountered so consider CONTINUE.
;; MAIN-6
L1373: INC (IY+$0D) ; increment SUBPPC to next statement.
;; MAIN-7
L1376: LD BC,$0003 ; prepare to copy 3 system variables to
LD DE,$5C70 ; address OSPPC - statement for CONTINUE.
; also updating OLDPPC line number below.
LD HL,$5C44 ; set source top to NSPPC next statement.
BIT 7,(HL) ; did BREAK occur before the jump ?
; e.g. between GO TO and next statement.
JR Z,L1384 ; skip forward to MAIN-8, if not, as set-up
; is correct.
ADD HL,BC ; set source to SUBPPC number of current
; statement/line which will be repeated.
;; MAIN-8
L1384: LDDR ; copy PPC to OLDPPC and SUBPPC to OSPCC
; or NSPPC to OLDPPC and NEWPPC to OSPCC
;; MAIN-9
L1386: LD (IY+$0A),$FF ; update NSPPC - signal 'no jump'.
RES 3,(IY+$01) ; update FLAGS - signal use 'K' mode for
; the first character in the editor and
JP L12AC ; jump back to MAIN-2.
; ----------------------
; Canned report messages
; ----------------------
; The Error reports with the last byte inverted. The first entry
; is a dummy entry. The last, which begins with $7F, the Spectrum
; character for copyright symbol, is placed here for convenience
; as is the preceding comma and space.
; The report line must accommodate a 4-digit line number and a 3-digit
; statement number which limits the length of the message text to twenty
; characters.
; e.g. "B Integer out of range, 1000:127"
;; rpt-mesgs
L1391: DEFB $80
DEFB 'O','K'+$80 ; 0
DEFM "NEXT without FO"
DEFB 'R'+$80 ; 1
DEFM "Variable not foun"
DEFB 'd'+$80 ; 2
DEFM "Subscript wron"
DEFB 'g'+$80 ; 3
DEFM "Out of memor"
DEFB 'y'+$80 ; 4
DEFM "Out of scree"
DEFB 'n'+$80 ; 5
DEFM "Number too bi"
DEFB 'g'+$80 ; 6
DEFM "RETURN without GOSU"
DEFB 'B'+$80 ; 7
DEFM "End of fil"
DEFB 'e'+$80 ; 8
DEFM "STOP statemen"
DEFB 't'+$80 ; 9
DEFM "Invalid argumen"
DEFB 't'+$80 ; A
DEFM "Integer out of rang"
DEFB 'e'+$80 ; B
DEFM "Nonsense in BASI"
DEFB 'C'+$80 ; C
DEFM "BREAK - CONT repeat"
DEFB 's'+$80 ; D
DEFM "Out of DAT"
DEFB 'A'+$80 ; E
DEFM "Invalid file nam"
DEFB 'e'+$80 ; F
DEFM "No room for lin"
DEFB 'e'+$80 ; G
DEFM "STOP in INPU"
DEFB 'T'+$80 ; H
DEFM "FOR without NEX"
DEFB 'T'+$80 ; I
DEFM "Invalid I/O devic"
DEFB 'e'+$80 ; J
DEFM "Invalid colou"
DEFB 'r'+$80 ; K
DEFM "BREAK into progra"
DEFB 'm'+$80 ; L
DEFM "RAMTOP no goo"
DEFB 'd'+$80 ; M
DEFM "Statement los"
DEFB 't'+$80 ; N
DEFM "Invalid strea"
DEFB 'm'+$80 ; O
DEFM "FN without DE"
DEFB 'F'+$80 ; P
DEFM "Parameter erro"
DEFB 'r'+$80 ; Q
DEFM "Tape loading erro"
DEFB 'r'+$80 ; R
;; comma-sp
L1537: DEFB ',',' '+$80 ; used in report line.
;; copyright
L1539: DEFB $7F ; copyright
DEFM " 1982 Sinclair Research Lt"
DEFB 'd'+$80
; -------------
; REPORT-G
; -------------
; Note ERR_SP points here during line entry which allows the
; normal 'Out of Memory' report to be augmented to the more
; precise 'No Room for line' report.
;; REPORT-G
; No Room for line
L1555: LD A,$10 ; i.e. 'G' -$30 -$07
LD BC,$0000 ; this seems unnecessary.
JP L1313 ; jump back to MAIN-G
; -----------------------------
; Handle addition of BASIC line
; -----------------------------
; Note this is not a subroutine but a branch of the main execution loop.
; System variable ERR_SP still points to editing error handler.
; A new line is added to the BASIC program at the appropriate place.
; An existing line with same number is deleted first.
; Entering an existing line number deletes that line.
; Entering a non-existent line allows the subsequent line to be edited next.
;; MAIN-ADD
L155D: LD ($5C49),BC ; set E_PPC to extracted line number.
LD HL,($5C5D) ; fetch CH_ADD - points to location after the
; initial digits (set in E_LINE_NO).
EX DE,HL ; save start of BASIC in DE.
LD HL,L1555 ; Address: REPORT-G
PUSH HL ; is pushed on stack and addressed by ERR_SP.
; the only error that can occur is
; 'Out of memory'.
LD HL,($5C61) ; fetch WORKSP - end of line.
SCF ; prepare for true subtraction.
SBC HL,DE ; find length of BASIC and
PUSH HL ; save it on stack.
LD H,B ; transfer line number
LD L,C ; to HL register.
CALL L196E ; routine LINE-ADDR will see if
; a line with the same number exists.
JR NZ,L157D ; forward if no existing line to MAIN-ADD1.
CALL L19B8 ; routine NEXT-ONE finds the existing line.
CALL L19E8 ; routine RECLAIM-2 reclaims it.
;; MAIN-ADD1
L157D: POP BC ; retrieve the length of the new line.
LD A,C ; and test if carriage return only
DEC A ; i.e. one byte long.
OR B ; result would be zero.
JR Z,L15AB ; forward to MAIN-ADD2 is so.
PUSH BC ; save the length again.
INC BC ; adjust for inclusion
INC BC ; of line number (two bytes)
INC BC ; and line length
INC BC ; (two bytes).
DEC HL ; HL points to location before the destination
LD DE,($5C53) ; fetch the address of PROG
PUSH DE ; and save it on the stack
CALL L1655 ; routine MAKE-ROOM creates BC spaces in
; program area and updates pointers.
POP HL ; restore old program pointer.
LD ($5C53),HL ; and put back in PROG as it may have been
; altered by the POINTERS routine.
POP BC ; retrieve BASIC length
PUSH BC ; and save again.
INC DE ; points to end of new area.
LD HL,($5C61) ; set HL to WORKSP - location after edit line.
DEC HL ; decrement to address end marker.
DEC HL ; decrement to address carriage return.
LDDR ; copy the BASIC line back to initial command.
LD HL,($5C49) ; fetch E_PPC - line number.
EX DE,HL ; swap it to DE, HL points to last of
; four locations.
POP BC ; retrieve length of line.
LD (HL),B ; high byte last.
DEC HL ;
LD (HL),C ; then low byte of length.
DEC HL ;
LD (HL),E ; then low byte of line number.
DEC HL ;
LD (HL),D ; then high byte range $0 - $27 (1-9999).
;; MAIN-ADD2
L15AB: POP AF ; drop the address of Report G
JP L12A2 ; and back to MAIN-EXEC producing a listing
; and to reset ERR_SP in EDITOR.
; ---------------------------------
; THE 'INITIAL CHANNEL' INFORMATION
; ---------------------------------
; This initial channel information is copied from ROM to RAM, during
; initialization. It's new location is after the system variables and is
; addressed by the system variable CHANS which means that it can slide up and
; down in memory. The table is never searched, by this ROM, and the last
; character, which could be anything other than a comma, provides a
; convenient resting place for DATADD.
;; init-chan
L15AF: DEFW L09F4 ; PRINT-OUT
DEFW L10A8 ; KEY-INPUT
DEFB $4B ; 'K'
DEFW L09F4 ; PRINT-OUT
DEFW L15C4 ; REPORT-J
DEFB $53 ; 'S'
DEFW L0F81 ; ADD-CHAR
DEFW L15C4 ; REPORT-J
DEFB $52 ; 'R'
DEFW L09F4 ; PRINT-OUT
DEFW L15C4 ; REPORT-J
DEFB $50 ; 'P'
DEFB $80 ; End Marker
;; REPORT-J
L15C4: RST 08H ; ERROR-1
DEFB $12 ; Error Report: Invalid I/O device
; -------------------------
; THE 'INITIAL STREAM' DATA
; -------------------------
; This is the initial stream data for the seven streams $FD - $03 that is
; copied from ROM to the STRMS system variables area during initialization.
; There are reserved locations there for another 12 streams. Each location
; contains an offset to the second byte of a channel. The first byte of a
; channel can't be used as that would result in an offset of zero for some
; and zero is used to denote that a stream is closed.
;; init-strm
L15C6: DEFB $01, $00 ; stream $FD offset to channel 'K'
DEFB $06, $00 ; stream $FE offset to channel 'S'
DEFB $0B, $00 ; stream $FF offset to channel 'R'
DEFB $01, $00 ; stream $00 offset to channel 'K'
DEFB $01, $00 ; stream $01 offset to channel 'K'
DEFB $06, $00 ; stream $02 offset to channel 'S'
DEFB $10, $00 ; stream $03 offset to channel 'P'
; ------------------------------
; THE 'INPUT CONTROL' SUBROUTINE
; ------------------------------
;
;; WAIT-KEY
L15D4: BIT 5,(IY+$02) ; test TV_FLAG - clear lower screen ?
JR NZ,L15DE ; forward to WAIT-KEY1 if so.
SET 3,(IY+$02) ; update TV_FLAG - signal reprint the edit
; line to the lower screen.
;; WAIT-KEY1
L15DE: CALL L15E6 ; routine INPUT-AD is called.
RET C ; return with acceptable keys.
JR Z,L15DE ; back to WAIT-KEY1 if no key is pressed
; or it has been handled within INPUT-AD.
; Note. When inputting from the keyboard all characters are returned with
; above conditions so this path is never taken.
;; REPORT-8
L15E4: RST 08H ; ERROR-1
DEFB $07 ; Error Report: End of file
; ---------------------------
; THE 'INPUT ADDRESS' ROUTINE
; ---------------------------
; This routine fetches the address of the input stream from the current
; channel area using the system variable CURCHL.
;; INPUT-AD
L15E6: EXX ; switch in alternate set.
PUSH HL ; save HL register
LD HL,($5C51) ; fetch address of CURCHL - current channel.
INC HL ; step over output routine
INC HL ; to point to low byte of input routine.
JR L15F7 ; forward to CALL-SUB.
; -------------------------
; THE 'CODE OUTPUT' ROUTINE
; -------------------------
; This routine is called on five occasions to print the ASCII equivalent of
; a value 0-9.
;; OUT-CODE
L15EF: LD E,$30 ; add 48 decimal to give the ASCII character
ADD A,E ; '0' to '9' and continue into the main output
; routine.
; -------------------------
; THE 'MAIN OUTPUT' ROUTINE
; -------------------------
; PRINT-A-2 is a continuation of the RST 10 restart that prints any character.
; The routine prints to the current channel and the printing of control codes
; may alter that channel to divert subsequent RST 10 instructions to temporary
; routines. The normal channel is $09F4.
;; PRINT-A-2
L15F2: EXX ; switch in alternate set
PUSH HL ; save HL register
LD HL,($5C51) ; fetch CURCHL the current channel.
; input-ad rejoins here also.
;; CALL-SUB
L15F7: LD E,(HL) ; put the low byte in E.
INC HL ; advance address.
LD D,(HL) ; put the high byte to D.
EX DE,HL ; transfer the stream to HL.
CALL L162C ; use routine CALL-JUMP.
; in effect CALL (HL).
POP HL ; restore saved HL register.
EXX ; switch back to the main set and
RET ; return.
; --------------------------
; THE 'OPEN CHANNEL' ROUTINE
; --------------------------
; This subroutine is used by the ROM to open a channel 'K', 'S', 'R' or 'P'.
; This is either for its own use or in response to a user's request, for
; example, when '#' is encountered with output - PRINT, LIST etc.
; or with input - INPUT, INKEY$ etc.
; It is entered with a system stream $FD - $FF, or a user stream $00 - $0F
; in the accumulator.
;; CHAN-OPEN
L1601: ADD A,A ; double the stream ($FF will become $FE etc.)
ADD A,$16 ; add the offset to stream 0 from $5C00
LD L,A ; result to L
LD H,$5C ; now form the address in STRMS area.
LD E,(HL) ; fetch low byte of CHANS offset
INC HL ; address next
LD D,(HL) ; fetch high byte of offset
LD A,D ; test that the stream is open.
OR E ; zero if closed.
JR NZ,L1610 ; forward to CHAN-OP-1 if open.
;; REPORT-Oa
L160E: RST 08H ; ERROR-1
DEFB $17 ; Error Report: Invalid stream
; continue here if stream was open. Note that the offset is from CHANS
; to the second byte of the channel.
;; CHAN-OP-1
L1610: DEC DE ; reduce offset so it points to the channel.
LD HL,($5C4F) ; fetch CHANS the location of the base of
; the channel information area
ADD HL,DE ; and add the offset to address the channel.
; and continue to set flags.
; -----------------
; Set channel flags
; -----------------
; This subroutine is used from ED-EDIT, str$ and read-in to reset the
; current channel when it has been temporarily altered.
;; CHAN-FLAG
L1615: LD ($5C51),HL ; set CURCHL system variable to the
; address in HL
RES 4,(IY+$30) ; update FLAGS2 - signal K channel not in use.
; Note. provide a default for channel 'R'.
INC HL ; advance past
INC HL ; output routine.
INC HL ; advance past
INC HL ; input routine.
LD C,(HL) ; pick up the letter.
LD HL,L162D ; address: chn-cd-lu
CALL L16DC ; routine INDEXER finds offset to a
; flag-setting routine.
RET NC ; but if the letter wasn't found in the
; table just return now. - channel 'R'.
LD D,$00 ; prepare to add
LD E,(HL) ; offset to E
ADD HL,DE ; add offset to location of offset to form
; address of routine
;; CALL-JUMP
L162C: JP (HL) ; jump to the routine
; Footnote. calling any location that holds JP (HL) is the equivalent to
; a pseudo Z80 instruction CALL (HL). The ROM uses the instruction above.
; --------------------------
; Channel code look-up table
; --------------------------
; This table is used by the routine above to find one of the three
; flag setting routines below it.
; A zero end-marker is required as channel 'R' is not present.
;; chn-cd-lu
L162D: DEFB 'K', L1634-$-1 ; offset $06 to CHAN-K
DEFB 'S', L1642-$-1 ; offset $12 to CHAN-S
DEFB 'P', L164D-$-1 ; offset $1B to CHAN-P
DEFB $00 ; end marker.
; --------------
; Channel K flag
; --------------
; routine to set flags for lower screen/keyboard channel.
;; CHAN-K
L1634: SET 0,(IY+$02) ; update TV_FLAG - signal lower screen in use
RES 5,(IY+$01) ; update FLAGS - signal no new key
SET 4,(IY+$30) ; update FLAGS2 - signal K channel in use
JR L1646 ; forward to CHAN-S-1 for indirect exit
; --------------
; Channel S flag
; --------------
; routine to set flags for upper screen channel.
;; CHAN-S
L1642: RES 0,(IY+$02) ; TV_FLAG - signal main screen in use
;; CHAN-S-1
L1646: RES 1,(IY+$01) ; update FLAGS - signal printer not in use
JP L0D4D ; jump back to TEMPS and exit via that
; routine after setting temporary attributes.
; --------------
; Channel P flag
; --------------
; This routine sets a flag so that subsequent print related commands
; print to printer or update the relevant system variables.
; This status remains in force until reset by the routine above.
;; CHAN-P
L164D: SET 1,(IY+$01) ; update FLAGS - signal printer in use
RET ; return
; --------------------------
; THE 'ONE SPACE' SUBROUTINE
; --------------------------
; This routine is called once only to create a single space
; in workspace by ADD-CHAR.
;; ONE-SPACE
L1652: LD BC,$0001 ; create space for a single character.
; ---------
; Make Room
; ---------
; This entry point is used to create BC spaces in various areas such as
; program area, variables area, workspace etc..
; The entire free RAM is available to each BASIC statement.
; On entry, HL addresses where the first location is to be created.
; Afterwards, HL will point to the location before this.
;; MAKE-ROOM
L1655: PUSH HL ; save the address pointer.
CALL L1F05 ; routine TEST-ROOM checks if room
; exists and generates an error if not.
POP HL ; restore the address pointer.
CALL L1664 ; routine POINTERS updates the
; dynamic memory location pointers.
; DE now holds the old value of STKEND.
LD HL,($5C65) ; fetch new STKEND the top destination.
EX DE,HL ; HL now addresses the top of the area to
; be moved up - old STKEND.
LDDR ; the program, variables, etc are moved up.
RET ; return with new area ready to be populated.
; HL points to location before new area,
; and DE to last of new locations.
; -----------------------------------------------
; Adjust pointers before making or reclaiming room
; -----------------------------------------------
; This routine is called by MAKE-ROOM to adjust upwards and by RECLAIM to
; adjust downwards the pointers within dynamic memory.
; The fourteen pointers to dynamic memory, starting with VARS and ending
; with STKEND, are updated adding BC if they are higher than the position
; in HL.
; The system variables are in no particular order except that STKEND, the first
; free location after dynamic memory must be the last encountered.
;; POINTERS
L1664: PUSH AF ; preserve accumulator.
PUSH HL ; put pos pointer on stack.
LD HL,$5C4B ; address VARS the first of the
LD A,$0E ; fourteen variables to consider.
;; PTR-NEXT
L166B: LD E,(HL) ; fetch the low byte of the system variable.
INC HL ; advance address.
LD D,(HL) ; fetch high byte of the system variable.
EX (SP),HL ; swap pointer on stack with the variable
; pointer.
AND A ; prepare to subtract.
SBC HL,DE ; subtract variable address
ADD HL,DE ; and add back
EX (SP),HL ; swap pos with system variable pointer
JR NC,L167F ; forward to PTR-DONE if var before pos
PUSH DE ; save system variable address.
EX DE,HL ; transfer to HL
ADD HL,BC ; add the offset
EX DE,HL ; back to DE
LD (HL),D ; load high byte
DEC HL ; move back
LD (HL),E ; load low byte
INC HL ; advance to high byte
POP DE ; restore old system variable address.
;; PTR-DONE
L167F: INC HL ; address next system variable.
DEC A ; decrease counter.
JR NZ,L166B ; back to PTR-NEXT if more.
EX DE,HL ; transfer old value of STKEND to HL.
; Note. this has always been updated.
POP DE ; pop the address of the position.
POP AF ; pop preserved accumulator.
AND A ; clear carry flag preparing to subtract.
SBC HL,DE ; subtract position from old stkend
LD B,H ; to give number of data bytes
LD C,L ; to be moved.
INC BC ; increment as we also copy byte at old STKEND.
ADD HL,DE ; recompute old stkend.
EX DE,HL ; transfer to DE.
RET ; return.
; -------------------
; Collect line number
; -------------------
; This routine extracts a line number, at an address that has previously
; been found using LINE-ADDR, and it is entered at LINE-NO. If it encounters
; the program 'end-marker' then the previous line is used and if that
; should also be unacceptable then zero is used as it must be a direct
; command. The program end-marker is the variables end-marker $80, or
; if variables exist, then the first character of any variable name.
;; LINE-ZERO
L168F: DEFB $00, $00 ; dummy line number used for direct commands
;; LINE-NO-A
L1691: EX DE,HL ; fetch the previous line to HL and set
LD DE,L168F ; DE to LINE-ZERO should HL also fail.
; -> The Entry Point.
;; LINE-NO
L1695: LD A,(HL) ; fetch the high byte - max $2F
AND $C0 ; mask off the invalid bits.
JR NZ,L1691 ; to LINE-NO-A if an end-marker.
LD D,(HL) ; reload the high byte.
INC HL ; advance address.
LD E,(HL) ; pick up the low byte.
RET ; return from here.
; -------------------
; Handle reserve room
; -------------------
; This is a continuation of the restart BC-SPACES
;; RESERVE
L169E: LD HL,($5C63) ; STKBOT first location of calculator stack
DEC HL ; make one less than new location
CALL L1655 ; routine MAKE-ROOM creates the room.
INC HL ; address the first new location
INC HL ; advance to second
POP BC ; restore old WORKSP
LD ($5C61),BC ; system variable WORKSP was perhaps
; changed by POINTERS routine.
POP BC ; restore count for return value.
EX DE,HL ; switch. DE = location after first new space
INC HL ; HL now location after new space
RET ; return.
; ---------------------------
; Clear various editing areas
; ---------------------------
; This routine sets the editing area, workspace and calculator stack
; to their minimum configurations as at initialization and indeed this
; routine could have been relied on to perform that task.
; This routine uses HL only and returns with that register holding
; WORKSP/STKBOT/STKEND though no use is made of this. The routines also
; reset MEM to its usual place in the systems variable area should it
; have been relocated to a FOR-NEXT variable. The main entry point
; SET-MIN is called at the start of the MAIN-EXEC loop and prior to
; displaying an error.
;; SET-MIN
L16B0: LD HL,($5C59) ; fetch E_LINE
LD (HL),$0D ; insert carriage return
LD ($5C5B),HL ; make K_CUR keyboard cursor point there.
INC HL ; next location
LD (HL),$80 ; holds end-marker $80
INC HL ; next location becomes
LD ($5C61),HL ; start of WORKSP
; This entry point is used prior to input and prior to the execution,
; or parsing, of each statement.
;; SET-WORK
L16BF: LD HL,($5C61) ; fetch WORKSP value
LD ($5C63),HL ; and place in STKBOT
; This entry point is used to move the stack back to its normal place
; after temporary relocation during line entry and also from ERROR-3
;; SET-STK
L16C5: LD HL,($5C63) ; fetch STKBOT value
LD ($5C65),HL ; and place in STKEND.
PUSH HL ; perhaps an obsolete entry point.
LD HL,$5C92 ; normal location of MEM-0
LD ($5C68),HL ; is restored to system variable MEM.
POP HL ; saved value not required.
RET ; return.
; ------------------
; Reclaim edit-line?
; ------------------
; This seems to be legacy code from the ZX80/ZX81 as it is
; not used in this ROM.
; That task, in fact, is performed here by the dual-area routine CLEAR-SP.
; This routine is designed to deal with something that is known to be in the
; edit buffer and not workspace.
; On entry, HL must point to the end of the something to be deleted.
;; REC-EDIT
L16D4: LD DE,($5C59) ; fetch start of edit line from E_LINE.
JP L19E5 ; jump forward to RECLAIM-1.
; --------------------------
; The Table INDEXING routine
; --------------------------
; This routine is used to search two-byte hash tables for a character
; held in C, returning the address of the following offset byte.
; if it is known that the character is in the table e.g. for priorities,
; then the table requires no zero end-marker. If this is not known at the
; outset then a zero end-marker is required and carry is set to signal
; success.
;; INDEXER-1
L16DB: INC HL ; address the next pair of values.
; -> The Entry Point.
;; INDEXER
L16DC: LD A,(HL) ; fetch the first byte of pair
AND A ; is it the end-marker ?
RET Z ; return with carry reset if so.
CP C ; is it the required character ?
INC HL ; address next location.
JR NZ,L16DB ; back to INDEXER-1 if no match.
SCF ; else set the carry flag.
RET ; return with carry set
; --------------------------------
; The Channel and Streams Routines
; --------------------------------
; A channel is an input/output route to a hardware device
; and is identified to the system by a single letter e.g. 'K' for
; the keyboard. A channel can have an input and output route
; associated with it in which case it is bi-directional like
; the keyboard. Others like the upper screen 'S' are output
; only and the input routine usually points to a report message.
; Channels 'K' and 'S' are system channels and it would be inappropriate
; to close the associated streams so a mechanism is provided to
; re-attach them. When the re-attachment is no longer required, then
; closing these streams resets them as at initialization.
; Early adverts said that the network and RS232 were in this ROM.
; Channels 'N' and 'B' are user channels and have been removed successfully
; if, as seems possible, they existed.
; Ironically the tape streamer is not accessed through streams and
; channels.
; Early demonstrations of the Spectrum showed a single microdrive being
; controlled by the main ROM.
; ---------------------
; THE 'CLOSE #' COMMAND
; ---------------------
; This command allows streams to be closed after use.
; Any temporary memory areas used by the stream would be reclaimed and
; finally flags set or reset if necessary.
;; CLOSE
L16E5: CALL L171E ; routine STR-DATA fetches parameter
; from calculator stack and gets the
; existing STRMS data pointer address in HL
; and stream offset from CHANS in BC.
; Note. this offset could be zero if the
; stream is already closed. A check for this
; should occur now and an error should be
; generated, for example,
; Report S 'Stream status closed'.
CALL L1701 ; routine CLOSE-2 would perform any actions
; peculiar to that stream without disturbing
; data pointer to STRMS entry in HL.
LD BC,$0000 ; the stream is to be blanked.
LD DE,$A3E2 ; the number of bytes from stream 4, $5C1E,
; to $10000
EX DE,HL ; transfer offset to HL, STRMS data pointer
; to DE.
ADD HL,DE ; add the offset to the data pointer.
JR C,L16FC ; forward to CLOSE-1 if a non-system stream.
; i.e. higher than 3.
; proceed with a negative result.
LD BC,L15C6 + 14 ; prepare the address of the byte after
; the initial stream data in ROM. ($15D4)
ADD HL,BC ; index into the data table with negative value.
LD C,(HL) ; low byte to C
INC HL ; address next.
LD B,(HL) ; high byte to B.
; and for streams 0 - 3 just enter the initial data back into the STRMS entry
; streams 0 - 2 can't be closed as they are shared by the operating system.
; -> for streams 4 - 15 then blank the entry.
;; CLOSE-1
L16FC: EX DE,HL ; address of stream to HL.
LD (HL),C ; place zero (or low byte).
INC HL ; next address.
LD (HL),B ; place zero (or high byte).
RET ; return.
; ------------------------
; THE 'CLOSE-2' SUBROUTINE
; ------------------------
; There is not much point in coming here.
; The purpose was once to find the offset to a special closing routine,
; in this ROM and within 256 bytes of the close stream look up table that
; would reclaim any buffers associated with a stream. At least one has been
; removed.
; Any attempt to CLOSE streams $00 to $04, without first opening the stream,
; will lead to either a system restart or the production of a strange report.
; credit: Martin Wren-Hilton 1982.
;; CLOSE-2
L1701: PUSH HL ; * save address of stream data pointer
; in STRMS on the machine stack.
LD HL,($5C4F) ; fetch CHANS address to HL
ADD HL,BC ; add the offset to address the second
; byte of the output routine hopefully.
INC HL ; step past
INC HL ; the input routine.
; Note. When the Sinclair Interface1 is fitted then an instruction fetch
; on the next address pages this ROM out and the shadow ROM in.
;; ROM_TRAP
L1708: INC HL ; to address channel's letter
LD C,(HL) ; pick it up in C.
; Note. but if stream is already closed we
; get the value $10 (the byte preceding 'K').
EX DE,HL ; save the pointer to the letter in DE.
; Note. The string pointer is saved but not used!!
LD HL,L1716 ; address: cl-str-lu in ROM.
CALL L16DC ; routine INDEXER uses the code to get
; the 8-bit offset from the current point to
; the address of the closing routine in ROM.
; Note. it won't find $10 there!
LD C,(HL) ; transfer the offset to C.
LD B,$00 ; prepare to add.
ADD HL,BC ; add offset to point to the address of the
; routine that closes the stream.
; (and presumably removes any buffers that
; are associated with it.)
JP (HL) ; jump to that routine.
; --------------------------------
; THE 'CLOSE STREAM LOOK-UP' TABLE
; --------------------------------
; This table contains an entry for a letter found in the CHANS area.
; followed by an 8-bit displacement, from that byte's address in the
; table to the routine that performs any ancillary actions associated
; with closing the stream of that channel.
; The table doesn't require a zero end-marker as the letter has been
; picked up from a channel that has an open stream.
;; cl-str-lu
L1716: DEFB 'K', L171C-$-1 ; offset 5 to CLOSE-STR
DEFB 'S', L171C-$-1 ; offset 3 to CLOSE-STR
DEFB 'P', L171C-$-1 ; offset 1 to CLOSE-STR
; ------------------------------
; THE 'CLOSE STREAM' SUBROUTINES
; ------------------------------
; The close stream routines in fact have no ancillary actions to perform
; which is not surprising with regard to 'K' and 'S'.
;; CLOSE-STR
L171C: POP HL ; * now just restore the stream data pointer
RET ; in STRMS and return.
; -----------
; Stream data
; -----------
; This routine finds the data entry in the STRMS area for the specified
; stream which is passed on the calculator stack. It returns with HL
; pointing to this system variable and BC holding a displacement from
; the CHANS area to the second byte of the stream's channel. If BC holds
; zero, then that signifies that the stream is closed.
;; STR-DATA
L171E: CALL L1E94 ; routine FIND-INT1 fetches parameter to A
CP $10 ; is it less than 16d ?
JR C,L1727 ; skip forward to STR-DATA1 if so.
;; REPORT-Ob
L1725: RST 08H ; ERROR-1
DEFB $17 ; Error Report: Invalid stream
;; STR-DATA1
L1727: ADD A,$03 ; add the offset for 3 system streams.
; range 00 - 15d becomes 3 - 18d.
RLCA ; double as there are two bytes per
; stream - now 06 - 36d
LD HL,$5C10 ; address STRMS - the start of the streams
; data area in system variables.
LD C,A ; transfer the low byte to A.
LD B,$00 ; prepare to add offset.
ADD HL,BC ; add to address the data entry in STRMS.
; the data entry itself contains an offset from CHANS to the address of the
; stream
LD C,(HL) ; low byte of displacement to C.
INC HL ; address next.
LD B,(HL) ; high byte of displacement to B.
DEC HL ; step back to leave HL pointing to STRMS
; data entry.
RET ; return with CHANS displacement in BC
; and address of stream data entry in HL.
; --------------------
; Handle OPEN# command
; --------------------
; Command syntax example: OPEN #5,"s"
; On entry the channel code entry is on the calculator stack with the next
; value containing the stream identifier. They have to swapped.
;; OPEN
L1736: RST 28H ;; FP-CALC ;s,c.
DEFB $01 ;;exchange ;c,s.
DEFB $38 ;;end-calc
CALL L171E ; routine STR-DATA fetches the stream off
; the stack and returns with the CHANS
; displacement in BC and HL addressing
; the STRMS data entry.
LD A,B ; test for zero which
OR C ; indicates the stream is closed.
JR Z,L1756 ; skip forward to OPEN-1 if so.
; if it is a system channel then it can re-attached.
EX DE,HL ; save STRMS address in DE.
LD HL,($5C4F) ; fetch CHANS.
ADD HL,BC ; add the offset to address the second
; byte of the channel.
INC HL ; skip over the
INC HL ; input routine.
INC HL ; and address the letter.
LD A,(HL) ; pick up the letter.
EX DE,HL ; save letter pointer and bring back
; the STRMS pointer.
CP $4B ; is it 'K' ?
JR Z,L1756 ; forward to OPEN-1 if so
CP $53 ; is it 'S' ?
JR Z,L1756 ; forward to OPEN-1 if so
CP $50 ; is it 'P' ?
JR NZ,L1725 ; back to REPORT-Ob if not.
; to report 'Invalid stream'.
; continue if one of the upper-case letters was found.
; and rejoin here from above if stream was closed.
;; OPEN-1
L1756: CALL L175D ; routine OPEN-2 opens the stream.
; it now remains to update the STRMS variable.
LD (HL),E ; insert or overwrite the low byte.
INC HL ; address high byte in STRMS.
LD (HL),D ; insert or overwrite the high byte.
RET ; return.
; -----------------
; OPEN-2 Subroutine
; -----------------
; There is some point in coming here as, as well as once creating buffers,
; this routine also sets flags.
;; OPEN-2
L175D: PUSH HL ; * save the STRMS data entry pointer.
CALL L2BF1 ; routine STK-FETCH now fetches the
; parameters of the channel string.
; start in DE, length in BC.
LD A,B ; test that it is not
OR C ; the null string.
JR NZ,L1767 ; skip forward to OPEN-3 with 1 character
; or more!
;; REPORT-Fb
L1765: RST 08H ; ERROR-1
DEFB $0E ; Error Report: Invalid file name
;; OPEN-3
L1767: PUSH BC ; save the length of the string.
LD A,(DE) ; pick up the first character.
; Note. There can be more than one character.
AND $DF ; make it upper-case.
LD C,A ; place it in C.
LD HL,L177A ; address: op-str-lu is loaded.
CALL L16DC ; routine INDEXER will search for letter.
JR NC,L1765 ; back to REPORT-F if not found
; 'Invalid filename'
LD C,(HL) ; fetch the displacement to opening routine.
LD B,$00 ; prepare to add.
ADD HL,BC ; now form address of opening routine.
POP BC ; restore the length of string.
JP (HL) ; now jump forward to the relevant routine.
; -------------------------
; OPEN stream look-up table
; -------------------------
; The open stream look-up table consists of matched pairs.
; The channel letter is followed by an 8-bit displacement to the
; associated stream-opening routine in this ROM.
; The table requires a zero end-marker as the letter has been
; provided by the user and not the operating system.
;; op-str-lu
L177A: DEFB 'K', L1781-$-1 ; $06 offset to OPEN-K
DEFB 'S', L1785-$-1 ; $08 offset to OPEN-S
DEFB 'P', L1789-$-1 ; $0A offset to OPEN-P
DEFB $00 ; end-marker.
; ----------------------------
; The Stream Opening Routines.
; ----------------------------
; These routines would have opened any buffers associated with the stream
; before jumping forward to OPEN-END with the displacement value in E
; and perhaps a modified value in BC. The strange pathing does seem to
; provide for flexibility in this respect.
;
; There is no need to open the printer buffer as it is there already
; even if you are still saving up for a ZX Printer or have moved onto
; something bigger. In any case it would have to be created after
; the system variables but apart from that it is a simple task
; and all but one of the ROM routines can handle a buffer in that position.
; (PR-ALL-6 would require an extra 3 bytes of code).
; However it wouldn't be wise to have two streams attached to the ZX Printer
; as you can now, so one assumes that if PR_CC_hi was non-zero then
; the OPEN-P routine would have refused to attach a stream if another
; stream was attached.
; Something of significance is being passed to these ghost routines in the
; second character. Strings 'RB', 'RT' perhaps or a drive/station number.
; The routine would have to deal with that and exit to OPEN_END with BC
; containing $0001 or more likely there would be an exit within the routine.
; Anyway doesn't matter, these routines are long gone.
; -----------------
; OPEN-K Subroutine
; -----------------
; Open Keyboard stream.
;; OPEN-K
L1781: LD E,$01 ; 01 is offset to second byte of channel 'K'.
JR L178B ; forward to OPEN-END
; -----------------
; OPEN-S Subroutine
; -----------------
; Open Screen stream.
;; OPEN-S
L1785: LD E,$06 ; 06 is offset to 2nd byte of channel 'S'
JR L178B ; to OPEN-END
; -----------------
; OPEN-P Subroutine
; -----------------
; Open Printer stream.
;; OPEN-P
L1789: LD E,$10 ; 16d is offset to 2nd byte of channel 'P'
;; OPEN-END
L178B: DEC BC ; the stored length of 'K','S','P' or
; whatever is now tested. ??
LD A,B ; test now if initial or residual length
OR C ; is one character.
JR NZ,L1765 ; to REPORT-Fb 'Invalid file name' if not.
LD D,A ; load D with zero to form the displacement
; in the DE register.
POP HL ; * restore the saved STRMS pointer.
RET ; return to update STRMS entry thereby
; signaling stream is open.
; ----------------------------------------
; Handle CAT, ERASE, FORMAT, MOVE commands
; ----------------------------------------
; These just generate an error report as the ROM is 'incomplete'.
;
; Luckily this provides a mechanism for extending these in a shadow ROM
; but without the powerful mechanisms set up in this ROM.
; An instruction fetch on $0008 may page in a peripheral ROM,
; e.g. the Sinclair Interface 1 ROM, to handle these commands.
; However that wasn't the plan.
; Development of this ROM continued for another three months until the cost
; of replacing it and the manual became unfeasible.
; The ultimate power of channels and streams died at birth.
;; CAT-ETC
L1793: JR L1725 ; to REPORT-Ob
; -----------------
; Perform AUTO-LIST
; -----------------
; This produces an automatic listing in the upper screen.
;; AUTO-LIST
L1795: LD ($5C3F),SP ; save stack pointer in LIST_SP
LD (IY+$02),$10 ; update TV_FLAG set bit 3
CALL L0DAF ; routine CL-ALL.
SET 0,(IY+$02) ; update TV_FLAG - signal lower screen in use
LD B,(IY+$31) ; fetch DF_SZ to B.
CALL L0E44 ; routine CL-LINE clears lower display
; preserving B.
RES 0,(IY+$02) ; update TV_FLAG - signal main screen in use
SET 0,(IY+$30) ; update FLAGS2 - signal will be necessary to
; clear main screen.
LD HL,($5C49) ; fetch E_PPC current edit line to HL.
LD DE,($5C6C) ; fetch S_TOP to DE, the current top line
; (initially zero)
AND A ; prepare for true subtraction.
SBC HL,DE ; subtract and
ADD HL,DE ; add back.
JR C,L17E1 ; to AUTO-L-2 if S_TOP higher than E_PPC
; to set S_TOP to E_PPC
PUSH DE ; save the top line number.
CALL L196E ; routine LINE-ADDR gets address of E_PPC.
LD DE,$02C0 ; prepare known number of characters in
; the default upper screen.
EX DE,HL ; offset to HL, program address to DE.
SBC HL,DE ; subtract high value from low to obtain
; negated result used in addition.
EX (SP),HL ; swap result with top line number on stack.
CALL L196E ; routine LINE-ADDR gets address of that
; top line in HL and next line in DE.
POP BC ; restore the result to balance stack.
;; AUTO-L-1
L17CE: PUSH BC ; save the result.
CALL L19B8 ; routine NEXT-ONE gets address in HL of
; line after auto-line (in DE).
POP BC ; restore result.
ADD HL,BC ; compute back.
JR C,L17E4 ; to AUTO-L-3 if line 'should' appear
EX DE,HL ; address of next line to HL.
LD D,(HL) ; get line
INC HL ; number
LD E,(HL) ; in DE.
DEC HL ; adjust back to start.
LD ($5C6C),DE ; update S_TOP.
JR L17CE ; to AUTO-L-1 until estimate reached.
; ---
; the jump was to here if S_TOP was greater than E_PPC
;; AUTO-L-2
L17E1: LD ($5C6C),HL ; make S_TOP the same as E_PPC.
; continue here with valid starting point from above or good estimate
; from computation
;; AUTO-L-3
L17E4: LD HL,($5C6C) ; fetch S_TOP line number to HL.
CALL L196E ; routine LINE-ADDR gets address in HL.
; address of next in DE.
JR Z,L17ED ; to AUTO-L-4 if line exists.
EX DE,HL ; else use address of next line.
;; AUTO-L-4
L17ED: CALL L1833 ; routine LIST-ALL >>>
; The return will be to here if no scrolling occurred
RES 4,(IY+$02) ; update TV_FLAG - signal no auto listing.
RET ; return.
; ------------
; Handle LLIST
; ------------
; A short form of LIST #3. The listing goes to stream 3 - default printer.
;; LLIST
L17F5: LD A,$03 ; the usual stream for ZX Printer
JR L17FB ; forward to LIST-1
; -----------
; Handle LIST
; -----------
; List to any stream.
; Note. While a starting line can be specified it is
; not possible to specify an end line.
; Just listing a line makes it the current edit line.
;; LIST
L17F9: LD A,$02 ; default is stream 2 - the upper screen.
;; LIST-1
L17FB: LD (IY+$02),$00 ; the TV_FLAG is initialized with bit 0 reset
; indicating upper screen in use.
CALL L2530 ; routine SYNTAX-Z - checking syntax ?
CALL NZ,L1601 ; routine CHAN-OPEN if in run-time.
RST 18H ; GET-CHAR
CALL L2070 ; routine STR-ALTER will alter if '#'.
JR C,L181F ; forward to LIST-4 not a '#' .
RST 18H ; GET-CHAR
CP $3B ; is it ';' ?
JR Z,L1814 ; skip to LIST-2 if so.
CP $2C ; is it ',' ?
JR NZ,L181A ; forward to LIST-3 if neither separator.
; we have, say, LIST #15, and a number must follow the separator.
;; LIST-2
L1814: RST 20H ; NEXT-CHAR
CALL L1C82 ; routine EXPT-1NUM
JR L1822 ; forward to LIST-5
; ---
; the branch was here with just LIST #3 etc.
;; LIST-3
L181A: CALL L1CE6 ; routine USE-ZERO
JR L1822 ; forward to LIST-5
; ---
; the branch was here with LIST
;; LIST-4
L181F: CALL L1CDE ; routine FETCH-NUM checks if a number
; follows else uses zero.
;; LIST-5
L1822: CALL L1BEE ; routine CHECK-END quits if syntax OK >>>
CALL L1E99 ; routine FIND-INT2 fetches the number
; from the calculator stack in run-time.
LD A,B ; fetch high byte of line number and
AND $3F ; make less than $40 so that NEXT-ONE
; (from LINE-ADDR) doesn't lose context.
; Note. this is not satisfactory and the typo
; LIST 20000 will list an entirely different
; section than LIST 2000. Such typos are not
; available for checking if they are direct
; commands.
LD H,A ; transfer the modified
LD L,C ; line number to HL.
LD ($5C49),HL ; update E_PPC to new line number.
CALL L196E ; routine LINE-ADDR gets the address of the
; line.
; This routine is called from AUTO-LIST
;; LIST-ALL
L1833: LD E,$01 ; signal current line not yet printed
;; LIST-ALL-2
L1835: CALL L1855 ; routine OUT-LINE outputs a BASIC line
; using PRINT-OUT and makes an early return
; when no more lines to print. >>>
RST 10H ; PRINT-A prints the carriage return (in A)
BIT 4,(IY+$02) ; test TV_FLAG - automatic listing ?
JR Z,L1835 ; back to LIST-ALL-2 if not
; (loop exit is via OUT-LINE)
; continue here if an automatic listing required.
LD A,($5C6B) ; fetch DF_SZ lower display file size.
SUB (IY+$4F) ; subtract S_POSN_hi ithe current line number.
JR NZ,L1835 ; back to LIST-ALL-2 if upper screen not full.
XOR E ; A contains zero, E contains one if the
; current edit line has not been printed
; or zero if it has (from OUT-LINE).
RET Z ; return if the screen is full and the line
; has been printed.
; continue with automatic listings if the screen is full and the current
; edit line is missing. OUT-LINE will scroll automatically.
PUSH HL ; save the pointer address.
PUSH DE ; save the E flag.
LD HL,$5C6C ; fetch S_TOP the rough estimate.
CALL L190F ; routine LN-FETCH updates S_TOP with
; the number of the next line.
POP DE ; restore the E flag.
POP HL ; restore the address of the next line.
JR L1835 ; back to LIST-ALL-2.
; ------------------------
; Print a whole BASIC line
; ------------------------
; This routine prints a whole BASIC line and it is called
; from LIST-ALL to output the line to current channel
; and from ED-EDIT to 'sprint' the line to the edit buffer.
;; OUT-LINE
L1855: LD BC,($5C49) ; fetch E_PPC the current line which may be
; unchecked and not exist.
CALL L1980 ; routine CP-LINES finds match or line after.
LD D,$3E ; prepare cursor '>' in D.
JR Z,L1865 ; to OUT-LINE1 if matched or line after.
LD DE,$0000 ; put zero in D, to suppress line cursor.
RL E ; pick up carry in E if line before current
; leave E zero if same or after.
;; OUT-LINE1
L1865: LD (IY+$2D),E ; save flag in BREG which is spare.
LD A,(HL) ; get high byte of line number.
CP $40 ; is it too high ($2F is maximum possible) ?
POP BC ; drop the return address and
RET NC ; make an early return if so >>>
PUSH BC ; save return address
CALL L1A28 ; routine OUT-NUM-2 to print addressed number
; with leading space.
INC HL ; skip low number byte.
INC HL ; and the two
INC HL ; length bytes.
RES 0,(IY+$01) ; update FLAGS - signal leading space required.
LD A,D ; fetch the cursor.
AND A ; test for zero.
JR Z,L1881 ; to OUT-LINE3 if zero.
RST 10H ; PRINT-A prints '>' the current line cursor.
; this entry point is called from ED-COPY
;; OUT-LINE2
L187D: SET 0,(IY+$01) ; update FLAGS - suppress leading space.
;; OUT-LINE3
L1881: PUSH DE ; save flag E for a return value.
EX DE,HL ; save HL address in DE.
RES 2,(IY+$30) ; update FLAGS2 - signal NOT in QUOTES.
LD HL,$5C3B ; point to FLAGS.
RES 2,(HL) ; signal 'K' mode. (starts before keyword)
BIT 5,(IY+$37) ; test FLAGX - input mode ?
JR Z,L1894 ; forward to OUT-LINE4 if not.
SET 2,(HL) ; signal 'L' mode. (used for input)
;; OUT-LINE4
L1894: LD HL,($5C5F) ; fetch X_PTR - possibly the error pointer
; address.
AND A ; clear the carry flag.
SBC HL,DE ; test if an error address has been reached.
JR NZ,L18A1 ; forward to OUT-LINE5 if not.
LD A,$3F ; load A with '?' the error marker.
CALL L18C1 ; routine OUT-FLASH to print flashing marker.
;; OUT-LINE5
L18A1: CALL L18E1 ; routine OUT-CURS will print the cursor if
; this is the right position.
EX DE,HL ; restore address pointer to HL.
LD A,(HL) ; fetch the addressed character.
CALL L18B6 ; routine NUMBER skips a hidden floating
; point number if present.
INC HL ; now increment the pointer.
CP $0D ; is character end-of-line ?
JR Z,L18B4 ; to OUT-LINE6, if so, as line is finished.
EX DE,HL ; save the pointer in DE.
CALL L1937 ; routine OUT-CHAR to output character/token.
JR L1894 ; back to OUT-LINE4 until entire line is done.
; ---
;; OUT-LINE6
L18B4: POP DE ; bring back the flag E, zero if current
; line printed else 1 if still to print.
RET ; return with A holding $0D
; -------------------------
; Check for a number marker
; -------------------------
; this subroutine is called from two processes. while outputting BASIC lines
; and while searching statements within a BASIC line.
; during both, this routine will pass over an invisible number indicator
; and the five bytes floating-point number that follows it.
; Note that this causes floating point numbers to be stripped from
; the BASIC line when it is fetched to the edit buffer by OUT_LINE.
; the number marker also appears after the arguments of a DEF FN statement
; and may mask old 5-byte string parameters.
;; NUMBER
L18B6: CP $0E ; character fourteen ?
RET NZ ; return if not.
INC HL ; skip the character
INC HL ; and five bytes
INC HL ; following.
INC HL ;
INC HL ;
INC HL ;
LD A,(HL) ; fetch the following character
RET ; for return value.
; --------------------------
; Print a flashing character
; --------------------------
; This subroutine is called from OUT-LINE to print a flashing error
; marker '?' or from the next routine to print a flashing cursor e.g. 'L'.
; However, this only gets called from OUT-LINE when printing the edit line
; or the input buffer to the lower screen so a direct call to $09F4 can
; be used, even though out-line outputs to other streams.
; In fact the alternate set is used for the whole routine.
;; OUT-FLASH
L18C1: EXX ; switch in alternate set
LD HL,($5C8F) ; fetch L = ATTR_T, H = MASK-T
PUSH HL ; save masks.
RES 7,H ; reset flash mask bit so active.
SET 7,L ; make attribute FLASH.
LD ($5C8F),HL ; resave ATTR_T and MASK-T
LD HL,$5C91 ; address P_FLAG
LD D,(HL) ; fetch to D
PUSH DE ; and save.
LD (HL),$00 ; clear inverse, over, ink/paper 9
CALL L09F4 ; routine PRINT-OUT outputs character
; without the need to vector via RST 10.
POP HL ; pop P_FLAG to H.
LD (IY+$57),H ; and restore system variable P_FLAG.
POP HL ; restore temporary masks
LD ($5C8F),HL ; and restore system variables ATTR_T/MASK_T
EXX ; switch back to main set
RET ; return
; ----------------
; Print the cursor
; ----------------
; This routine is called before any character is output while outputting
; a BASIC line or the input buffer. This includes listing to a printer
; or screen, copying a BASIC line to the edit buffer and printing the
; input buffer or edit buffer to the lower screen. It is only in the
; latter two cases that it has any relevance and in the last case it
; performs another very important function also.
;; OUT-CURS
L18E1: LD HL,($5C5B) ; fetch K_CUR the current cursor address
AND A ; prepare for true subtraction.
SBC HL,DE ; test against pointer address in DE and
RET NZ ; return if not at exact position.
; the value of MODE, maintained by KEY-INPUT, is tested and if non-zero
; then this value 'E' or 'G' will take precedence.
LD A,($5C41) ; fetch MODE 0='KLC', 1='E', 2='G'.
RLC A ; double the value and set flags.
JR Z,L18F3 ; to OUT-C-1 if still zero ('KLC').
ADD A,$43 ; add 'C' - will become 'E' if originally 1
; or 'G' if originally 2.
JR L1909 ; forward to OUT-C-2 to print.
; ---
; If mode was zero then, while printing a BASIC line, bit 2 of flags has been
; set if 'THEN' or ':' was encountered as a main character and reset otherwise.
; This is now used to determine if the 'K' cursor is to be printed but this
; transient state is also now transferred permanently to bit 3 of FLAGS
; to let the interrupt routine know how to decode the next key.
;; OUT-C-1
L18F3: LD HL,$5C3B ; Address FLAGS
RES 3,(HL) ; signal 'K' mode initially.
LD A,$4B ; prepare letter 'K'.
BIT 2,(HL) ; test FLAGS - was the
; previous main character ':' or 'THEN' ?
JR Z,L1909 ; forward to OUT-C-2 if so to print.
SET 3,(HL) ; signal 'L' mode to interrupt routine.
; Note. transient bit has been made permanent.
INC A ; augment from 'K' to 'L'.
BIT 3,(IY+$30) ; test FLAGS2 - consider caps lock ?
; which is maintained by KEY-INPUT.
JR Z,L1909 ; forward to OUT-C-2 if not set to print.
LD A,$43 ; alter 'L' to 'C'.
;; OUT-C-2
L1909: PUSH DE ; save address pointer but OK as OUT-FLASH
; uses alternate set without RST 10.
CALL L18C1 ; routine OUT-FLASH to print.
POP DE ; restore and
RET ; return.
; ----------------------------
; Get line number of next line
; ----------------------------
; These two subroutines are called while editing.
; This entry point is from ED-DOWN with HL addressing E_PPC
; to fetch the next line number.
; Also from AUTO-LIST with HL addressing S_TOP just to update S_TOP
; with the value of the next line number. It gets fetched but is discarded.
; These routines never get called while the editor is being used for input.
;; LN-FETCH
L190F: LD E,(HL) ; fetch low byte
INC HL ; address next
LD D,(HL) ; fetch high byte.
PUSH HL ; save system variable hi pointer.
EX DE,HL ; line number to HL,
INC HL ; increment as a starting point.
CALL L196E ; routine LINE-ADDR gets address in HL.
CALL L1695 ; routine LINE-NO gets line number in DE.
POP HL ; restore system variable hi pointer.
; This entry point is from the ED-UP with HL addressing E_PPC_hi
;; LN-STORE
L191C: BIT 5,(IY+$37) ; test FLAGX - input mode ?
RET NZ ; return if so.
; Note. above already checked by ED-UP/ED-DOWN.
LD (HL),D ; save high byte of line number.
DEC HL ; address lower
LD (HL),E ; save low byte of line number.
RET ; return.
; -----------------------------------------
; Outputting numbers at start of BASIC line
; -----------------------------------------
; This routine entered at OUT-SP-NO is used to compute then output the first
; three digits of a 4-digit BASIC line printing a space if necessary.
; The line number, or residual part, is held in HL and the BC register
; holds a subtraction value -1000, -100 or -10.
; Note. for example line number 200 -
; space(out_char), 2(out_code), 0(out_char) final number always out-code.
;; OUT-SP-2
L1925: LD A,E ; will be space if OUT-CODE not yet called.
; or $FF if spaces are suppressed.
; else $30 ('0').
; (from the first instruction at OUT-CODE)
; this guy is just too clever.
AND A ; test bit 7 of A.
RET M ; return if $FF, as leading spaces not
; required. This is set when printing line
; number and statement in MAIN-5.
JR L1937 ; forward to exit via OUT-CHAR.
; ---
; -> the single entry point.
;; OUT-SP-NO
L192A: XOR A ; initialize digit to 0
;; OUT-SP-1
L192B: ADD HL,BC ; add negative number to HL.
INC A ; increment digit
JR C,L192B ; back to OUT-SP-1 until no carry from
; the addition.
SBC HL,BC ; cancel the last addition
DEC A ; and decrement the digit.
JR Z,L1925 ; back to OUT-SP-2 if it is zero.
JP L15EF ; jump back to exit via OUT-CODE. ->
; -------------------------------------
; Outputting characters in a BASIC line
; -------------------------------------
; This subroutine ...
;; OUT-CHAR
L1937: CALL L2D1B ; routine NUMERIC tests if it is a digit ?
JR NC,L196C ; to OUT-CH-3 to print digit without
; changing mode. Will be 'K' mode if digits
; are at beginning of edit line.
CP $21 ; less than quote character ?
JR C,L196C ; to OUT-CH-3 to output controls and space.
RES 2,(IY+$01) ; initialize FLAGS to 'K' mode and leave
; unchanged if this character would precede
; a keyword.
CP $CB ; is character 'THEN' token ?
JR Z,L196C ; to OUT-CH-3 to output if so.
CP $3A ; is it ':' ?
JR NZ,L195A ; to OUT-CH-1 if not statement separator
; to change mode back to 'L'.
BIT 5,(IY+$37) ; FLAGX - Input Mode ??
JR NZ,L1968 ; to OUT-CH-2 if in input as no statements.
; Note. this check should seemingly be at
; the start. Commands seem inappropriate in
; INPUT mode and are rejected by the syntax
; checker anyway.
; unless INPUT LINE is being used.
BIT 2,(IY+$30) ; test FLAGS2 - is the ':' within quotes ?
JR Z,L196C ; to OUT-CH-3 if ':' is outside quoted text.
JR L1968 ; to OUT-CH-2 as ':' is within quotes
; ---
;; OUT-CH-1
L195A: CP $22 ; is it quote character '"' ?
JR NZ,L1968 ; to OUT-CH-2 with others to set 'L' mode.
PUSH AF ; save character.
LD A,($5C6A) ; fetch FLAGS2.
XOR $04 ; toggle the quotes flag.
LD ($5C6A),A ; update FLAGS2
POP AF ; and restore character.
;; OUT-CH-2
L1968: SET 2,(IY+$01) ; update FLAGS - signal L mode if the cursor
; is next.
;; OUT-CH-3
L196C: RST 10H ; PRINT-A vectors the character to
; channel 'S', 'K', 'R' or 'P'.
RET ; return.
; -------------------------------------------
; Get starting address of line, or line after
; -------------------------------------------
; This routine is used often to get the address, in HL, of a BASIC line
; number supplied in HL, or failing that the address of the following line
; and the address of the previous line in DE.
;; LINE-ADDR
L196E: PUSH HL ; save line number in HL register
LD HL,($5C53) ; fetch start of program from PROG
LD D,H ; transfer address to
LD E,L ; the DE register pair.
;; LINE-AD-1
L1974: POP BC ; restore the line number to BC
CALL L1980 ; routine CP-LINES compares with that
; addressed by HL
RET NC ; return if line has been passed or matched.
; if NZ, address of previous is in DE
PUSH BC ; save the current line number
CALL L19B8 ; routine NEXT-ONE finds address of next
; line number in DE, previous in HL.
EX DE,HL ; switch so next in HL
JR L1974 ; back to LINE-AD-1 for another comparison
; --------------------
; Compare line numbers
; --------------------
; This routine compares a line number supplied in BC with an addressed
; line number pointed to by HL.
;; CP-LINES
L1980: LD A,(HL) ; Load the high byte of line number and
CP B ; compare with that of supplied line number.
RET NZ ; return if yet to match (carry will be set).
INC HL ; address low byte of
LD A,(HL) ; number and pick up in A.
DEC HL ; step back to first position.
CP C ; now compare.
RET ; zero set if exact match.
; carry set if yet to match.
; no carry indicates a match or
; next available BASIC line or
; program end marker.
; -------------------
; Find each statement
; -------------------
; The single entry point EACH-STMT is used to
; 1) To find the D'th statement in a line.
; 2) To find a token in held E.
;; not-used
L1988: INC HL ;
INC HL ;
INC HL ;
; -> entry point.
;; EACH-STMT
L198B: LD ($5C5D),HL ; save HL in CH_ADD
LD C,$00 ; initialize quotes flag
;; EACH-S-1
L1990: DEC D ; decrease statement count
RET Z ; return if zero
RST 20H ; NEXT-CHAR
CP E ; is it the search token ?
JR NZ,L199A ; forward to EACH-S-3 if not
AND A ; clear carry
RET ; return signalling success.
; ---
;; EACH-S-2
L1998: INC HL ; next address
LD A,(HL) ; next character
;; EACH-S-3
L199A: CALL L18B6 ; routine NUMBER skips if number marker
LD ($5C5D),HL ; save in CH_ADD
CP $22 ; is it quotes '"' ?
JR NZ,L19A5 ; to EACH-S-4 if not
DEC C ; toggle bit 0 of C
;; EACH-S-4
L19A5: CP $3A ; is it ':'
JR Z,L19AD ; to EACH-S-5
CP $CB ; 'THEN'
JR NZ,L19B1 ; to EACH-S-6
;; EACH-S-5
L19AD: BIT 0,C ; is it in quotes
JR Z,L1990 ; to EACH-S-1 if not
;; EACH-S-6
L19B1: CP $0D ; end of line ?
JR NZ,L1998 ; to EACH-S-2
DEC D ; decrease the statement counter
; which should be zero else
; 'Statement Lost'.
SCF ; set carry flag - not found
RET ; return
; -----------------------------------------------------------------------
; Storage of variables. For full details - see chapter 24.
; ZX Spectrum BASIC Programming by Steven Vickers 1982.
; It is bits 7-5 of the first character of a variable that allow
; the six types to be distinguished. Bits 4-0 are the reduced letter.
; So any variable name is higher that $3F and can be distinguished
; also from the variables area end-marker $80.
;
; 76543210 meaning brief outline of format.
; -------- ------------------------ -----------------------
; 010 string variable. 2 byte length + contents.
; 110 string array. 2 byte length + contents.
; 100 array of numbers. 2 byte length + contents.
; 011 simple numeric variable. 5 bytes.
; 101 variable length named numeric. 5 bytes.
; 111 for-next loop variable. 18 bytes.
; 10000000 the variables area end-marker.
;
; Note. any of the above seven will serve as a program end-marker.
;
; -----------------------------------------------------------------------
; ------------
; Get next one
; ------------
; This versatile routine is used to find the address of the next line
; in the program area or the next variable in the variables area.
; The reason one routine is made to handle two apparently unrelated tasks
; is that it can be called indiscriminately when merging a line or a
; variable.
;; NEXT-ONE
L19B8: PUSH HL ; save the pointer address.
LD A,(HL) ; get first byte.
CP $40 ; compare with upper limit for line numbers.
JR C,L19D5 ; forward to NEXT-O-3 if within BASIC area.
; the continuation here is for the next variable unless the supplied
; line number was erroneously over 16383. see RESTORE command.
BIT 5,A ; is it a string or an array variable ?
JR Z,L19D6 ; forward to NEXT-O-4 to compute length.
ADD A,A ; test bit 6 for single-character variables.
JP M,L19C7 ; forward to NEXT-O-1 if so
CCF ; clear the carry for long-named variables.
; it remains set for for-next loop variables.
;; NEXT-O-1
L19C7: LD BC,$0005 ; set BC to 5 for floating point number
JR NC,L19CE ; forward to NEXT-O-2 if not a for/next
; variable.
LD C,$12 ; set BC to eighteen locations.
; value, limit, step, line and statement.
; now deal with long-named variables
;; NEXT-O-2
L19CE: RLA ; test if character inverted. carry will also
; be set for single character variables
INC HL ; address next location.
LD A,(HL) ; and load character.
JR NC,L19CE ; back to NEXT-O-2 if not inverted bit.
; forward immediately with single character
; variable names.
JR L19DB ; forward to NEXT-O-5 to add length of
; floating point number(s etc.).
; ---
; this branch is for line numbers.
;; NEXT-O-3
L19D5: INC HL ; increment pointer to low byte of line no.
; strings and arrays rejoin here
;; NEXT-O-4
L19D6: INC HL ; increment to address the length low byte.
LD C,(HL) ; transfer to C and
INC HL ; point to high byte of length.
LD B,(HL) ; transfer that to B
INC HL ; point to start of BASIC/variable contents.
; the three types of numeric variables rejoin here
;; NEXT-O-5
L19DB: ADD HL,BC ; add the length to give address of next
; line/variable in HL.
POP DE ; restore previous address to DE.
; ------------------
; Difference routine
; ------------------
; This routine terminates the above routine and is also called from the
; start of the next routine to calculate the length to reclaim.
;; DIFFER
L19DD: AND A ; prepare for true subtraction.
SBC HL,DE ; subtract the two pointers.
LD B,H ; transfer result
LD C,L ; to BC register pair.
ADD HL,DE ; add back
EX DE,HL ; and switch pointers
RET ; return values are the length of area in BC,
; low pointer (previous) in HL,
; high pointer (next) in DE.
; -----------------------
; Handle reclaiming space
; -----------------------
;
;; RECLAIM-1
L19E5: CALL L19DD ; routine DIFFER immediately above
;; RECLAIM-2
L19E8: PUSH BC ;
LD A,B ;
CPL ;
LD B,A ;
LD A,C ;
CPL ;
LD C,A ;
INC BC ;
CALL L1664 ; routine POINTERS
EX DE,HL ;
POP HL ;
ADD HL,DE ;
PUSH DE ;
LDIR ; copy bytes
POP HL ;
RET ;
; ----------------------------------------
; Read line number of line in editing area
; ----------------------------------------
; This routine reads a line number in the editing area returning the number
; in the BC register or zero if no digits exist before commands.
; It is called from LINE-SCAN to check the syntax of the digits.
; It is called from MAIN-3 to extract the line number in preparation for
; inclusion of the line in the BASIC program area.
;
; Interestingly the calculator stack is moved from its normal place at the
; end of dynamic memory to an adequate area within the system variables area.
; This ensures that in a low memory situation, that valid line numbers can
; be extracted without raising an error and that memory can be reclaimed
; by deleting lines. If the stack was in its normal place then a situation
; arises whereby the Spectrum becomes locked with no means of reclaiming space.
;; E-LINE-NO
L19FB: LD HL,($5C59) ; load HL from system variable E_LINE.
DEC HL ; decrease so that NEXT_CHAR can be used
; without skipping the first digit.
LD ($5C5D),HL ; store in the system variable CH_ADD.
RST 20H ; NEXT-CHAR skips any noise and white-space
; to point exactly at the first digit.
LD HL,$5C92 ; use MEM-0 as a temporary calculator stack
; an overhead of three locations are needed.
LD ($5C65),HL ; set new STKEND.
CALL L2D3B ; routine INT-TO-FP will read digits till
; a non-digit found.
CALL L2DA2 ; routine FP-TO-BC will retrieve number
; from stack at membot.
JR C,L1A15 ; forward to E-L-1 if overflow i.e. > 65535.
; 'Nonsense in BASIC'
LD HL,$D8F0 ; load HL with value -9999
ADD HL,BC ; add to line number in BC
;; E-L-1
L1A15: JP C,L1C8A ; to REPORT-C 'Nonsense in BASIC' if over.
; Note. As ERR_SP points to ED_ERROR
; the report is never produced although
; the RST $08 will update X_PTR leading to
; the error marker being displayed when
; the ED_LOOP is reiterated.
; in fact, since it is immediately
; cancelled, any report will do.
; a line in the range 0 - 9999 has been entered.
JP L16C5 ; jump back to SET-STK to set the calculator
; stack back to its normal place and exit
; from there.
; ---------------------------------
; Report and line number outputting
; ---------------------------------
; Entry point OUT-NUM-1 is used by the Error Reporting code to print
; the line number and later the statement number held in BC.
; If the statement was part of a direct command then -2 is used as a
; dummy line number so that zero will be printed in the report.
; This routine is also used to print the exponent of E-format numbers.
;
; Entry point OUT-NUM-2 is used from OUT-LINE to output the line number
; addressed by HL with leading spaces if necessary.
;; OUT-NUM-1
L1A1B: PUSH DE ; save the
PUSH HL ; registers.
XOR A ; set A to zero.
BIT 7,B ; is the line number minus two ?
JR NZ,L1A42 ; forward to OUT-NUM-4 if so to print zero
; for a direct command.
LD H,B ; transfer the
LD L,C ; number to HL.
LD E,$FF ; signal 'no leading zeros'.
JR L1A30 ; forward to continue at OUT-NUM-3
; ---
; from OUT-LINE - HL addresses line number.
;; OUT-NUM-2
L1A28: PUSH DE ; save flags
LD D,(HL) ; high byte to D
INC HL ; address next
LD E,(HL) ; low byte to E
PUSH HL ; save pointer
EX DE,HL ; transfer number to HL
LD E,$20 ; signal 'output leading spaces'
;; OUT-NUM-3
L1A30: LD BC,$FC18 ; value -1000
CALL L192A ; routine OUT-SP-NO outputs space or number
LD BC,$FF9C ; value -100
CALL L192A ; routine OUT-SP-NO
LD C,$F6 ; value -10 ( B is still $FF )
CALL L192A ; routine OUT-SP-NO
LD A,L ; remainder to A.
;; OUT-NUM-4
L1A42: CALL L15EF ; routine OUT-CODE for final digit.
; else report code zero wouldn't get
; printed.
POP HL ; restore the
POP DE ; registers and
RET ; return.
;***************************************************
;** Part 7. BASIC LINE AND COMMAND INTERPRETATION **
;***************************************************
; ----------------
; The offset table
; ----------------
; The BASIC interpreter has found a command code $CE - $FF
; which is then reduced to range $00 - $31 and added to the base address
; of this table to give the address of an offset which, when added to
; the offset therein, gives the location in the following parameter table
; where a list of class codes, separators and addresses relevant to the
; command exists.
;; offst-tbl
L1A48: DEFB L1AF9 - $ ; B1 offset to Address: P-DEF-FN
DEFB L1B14 - $ ; CB offset to Address: P-CAT
DEFB L1B06 - $ ; BC offset to Address: P-FORMAT
DEFB L1B0A - $ ; BF offset to Address: P-MOVE
DEFB L1B10 - $ ; C4 offset to Address: P-ERASE
DEFB L1AFC - $ ; AF offset to Address: P-OPEN
DEFB L1B02 - $ ; B4 offset to Address: P-CLOSE
DEFB L1AE2 - $ ; 93 offset to Address: P-MERGE
DEFB L1AE1 - $ ; 91 offset to Address: P-VERIFY
DEFB L1AE3 - $ ; 92 offset to Address: P-BEEP
DEFB L1AE7 - $ ; 95 offset to Address: P-CIRCLE
DEFB L1AEB - $ ; 98 offset to Address: P-INK
DEFB L1AEC - $ ; 98 offset to Address: P-PAPER
DEFB L1AED - $ ; 98 offset to Address: P-FLASH
DEFB L1AEE - $ ; 98 offset to Address: P-BRIGHT
DEFB L1AEF - $ ; 98 offset to Address: P-INVERSE
DEFB L1AF0 - $ ; 98 offset to Address: P-OVER
DEFB L1AF1 - $ ; 98 offset to Address: P-OUT
DEFB L1AD9 - $ ; 7F offset to Address: P-LPRINT
DEFB L1ADC - $ ; 81 offset to Address: P-LLIST
DEFB L1A8A - $ ; 2E offset to Address: P-STOP
DEFB L1AC9 - $ ; 6C offset to Address: P-READ
DEFB L1ACC - $ ; 6E offset to Address: P-DATA
DEFB L1ACF - $ ; 70 offset to Address: P-RESTORE
DEFB L1AA8 - $ ; 48 offset to Address: P-NEW
DEFB L1AF5 - $ ; 94 offset to Address: P-BORDER
DEFB L1AB8 - $ ; 56 offset to Address: P-CONT
DEFB L1AA2 - $ ; 3F offset to Address: P-DIM
DEFB L1AA5 - $ ; 41 offset to Address: P-REM
DEFB L1A90 - $ ; 2B offset to Address: P-FOR
DEFB L1A7D - $ ; 17 offset to Address: P-GO-TO
DEFB L1A86 - $ ; 1F offset to Address: P-GO-SUB
DEFB L1A9F - $ ; 37 offset to Address: P-INPUT
DEFB L1AE0 - $ ; 77 offset to Address: P-LOAD
DEFB L1AAE - $ ; 44 offset to Address: P-LIST
DEFB L1A7A - $ ; 0F offset to Address: P-LET
DEFB L1AC5 - $ ; 59 offset to Address: P-PAUSE
DEFB L1A98 - $ ; 2B offset to Address: P-NEXT
DEFB L1AB1 - $ ; 43 offset to Address: P-POKE
DEFB L1A9C - $ ; 2D offset to Address: P-PRINT
DEFB L1AC1 - $ ; 51 offset to Address: P-PLOT
DEFB L1AAB - $ ; 3A offset to Address: P-RUN
DEFB L1ADF - $ ; 6D offset to Address: P-SAVE
DEFB L1AB5 - $ ; 42 offset to Address: P-RANDOM
DEFB L1A81 - $ ; 0D offset to Address: P-IF
DEFB L1ABE - $ ; 49 offset to Address: P-CLS
DEFB L1AD2 - $ ; 5C offset to Address: P-DRAW
DEFB L1ABB - $ ; 44 offset to Address: P-CLEAR
DEFB L1A8D - $ ; 15 offset to Address: P-RETURN
DEFB L1AD6 - $ ; 5D offset to Address: P-COPY
; -------------------------------
; The parameter or "Syntax" table
; -------------------------------
; For each command there exists a variable list of parameters.
; If the character is greater than a space it is a required separator.
; If less, then it is a command class in the range 00 - 0B.
; Note that classes 00, 03 and 05 will fetch the addresses from this table.
; Some classes e.g. 07 and 0B have the same address in all invocations
; and the command is re-computed from the low-byte of the parameter address.
; Some e.g. 02 are only called once so a call to the command is made from
; within the class routine rather than holding the address within the table.
; Some class routines check syntax entirely and some leave this task for the
; command itself.
; Others for example CIRCLE (x,y,z) check the first part (x,y) using the
; class routine and the final part (,z) within the command.
; The last few commands appear to have been added in a rush but their syntax
; is rather simple e.g. MOVE "M1","M2"
;; P-LET
L1A7A: DEFB $01 ; Class-01 - A variable is required.
DEFB $3D ; Separator: '='
DEFB $02 ; Class-02 - An expression, numeric or string,
; must follow.
;; P-GO-TO
L1A7D: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1E67 ; Address: $1E67; Address: GO-TO
;; P-IF
L1A81: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $CB ; Separator: 'THEN'
DEFB $05 ; Class-05 - Variable syntax checked
; by routine.
DEFW L1CF0 ; Address: $1CF0; Address: IF
;; P-GO-SUB
L1A86: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1EED ; Address: $1EED; Address: GO-SUB
;; P-STOP
L1A8A: DEFB $00 ; Class-00 - No further operands.
DEFW L1CEE ; Address: $1CEE; Address: STOP
;; P-RETURN
L1A8D: DEFB $00 ; Class-00 - No further operands.
DEFW L1F23 ; Address: $1F23; Address: RETURN
;; P-FOR
L1A90: DEFB $04 ; Class-04 - A single character variable must
; follow.
DEFB $3D ; Separator: '='
DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $CC ; Separator: 'TO'
DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $05 ; Class-05 - Variable syntax checked
; by routine.
DEFW L1D03 ; Address: $1D03; Address: FOR
;; P-NEXT
L1A98: DEFB $04 ; Class-04 - A single character variable must
; follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1DAB ; Address: $1DAB; Address: NEXT
;; P-PRINT
L1A9C: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1FCD ; Address: $1FCD; Address: PRINT
;; P-INPUT
L1A9F: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L2089 ; Address: $2089; Address: INPUT
;; P-DIM
L1AA2: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L2C02 ; Address: $2C02; Address: DIM
;; P-REM
L1AA5: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1BB2 ; Address: $1BB2; Address: REM
;; P-NEW
L1AA8: DEFB $00 ; Class-00 - No further operands.
DEFW L11B7 ; Address: $11B7; Address: NEW
;; P-RUN
L1AAB: DEFB $03 ; Class-03 - A numeric expression may follow
; else default to zero.
DEFW L1EA1 ; Address: $1EA1; Address: RUN
;; P-LIST
L1AAE: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L17F9 ; Address: $17F9; Address: LIST
;; P-POKE
L1AB1: DEFB $08 ; Class-08 - Two comma-separated numeric
; expressions required.
DEFB $00 ; Class-00 - No further operands.
DEFW L1E80 ; Address: $1E80; Address: POKE
;; P-RANDOM
L1AB5: DEFB $03 ; Class-03 - A numeric expression may follow
; else default to zero.
DEFW L1E4F ; Address: $1E4F; Address: RANDOMIZE
;; P-CONT
L1AB8: DEFB $00 ; Class-00 - No further operands.
DEFW L1E5F ; Address: $1E5F; Address: CONTINUE
;; P-CLEAR
L1ABB: DEFB $03 ; Class-03 - A numeric expression may follow
; else default to zero.
DEFW L1EAC ; Address: $1EAC; Address: CLEAR
;; P-CLS
L1ABE: DEFB $00 ; Class-00 - No further operands.
DEFW L0D6B ; Address: $0D6B; Address: CLS
;; P-PLOT
L1AC1: DEFB $09 ; Class-09 - Two comma-separated numeric
; expressions required with optional colour
; items.
DEFB $00 ; Class-00 - No further operands.
DEFW L22DC ; Address: $22DC; Address: PLOT
;; P-PAUSE
L1AC5: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1F3A ; Address: $1F3A; Address: PAUSE
;; P-READ
L1AC9: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1DED ; Address: $1DED; Address: READ
;; P-DATA
L1ACC: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1E27 ; Address: $1E27; Address: DATA
;; P-RESTORE
L1ACF: DEFB $03 ; Class-03 - A numeric expression may follow
; else default to zero.
DEFW L1E42 ; Address: $1E42; Address: RESTORE
;; P-DRAW
L1AD2: DEFB $09 ; Class-09 - Two comma-separated numeric
; expressions required with optional colour
; items.
DEFB $05 ; Class-05 - Variable syntax checked
; by routine.
DEFW L2382 ; Address: $2382; Address: DRAW
;; P-COPY
L1AD6: DEFB $00 ; Class-00 - No further operands.
DEFW L0EAC ; Address: $0EAC; Address: COPY
;; P-LPRINT
L1AD9: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1FC9 ; Address: $1FC9; Address: LPRINT
;; P-LLIST
L1ADC: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L17F5 ; Address: $17F5; Address: LLIST
;; P-SAVE
L1ADF: DEFB $0B ; Class-0B - Offset address converted to tape
; command.
;; P-LOAD
L1AE0: DEFB $0B ; Class-0B - Offset address converted to tape
; command.
;; P-VERIFY
L1AE1: DEFB $0B ; Class-0B - Offset address converted to tape
; command.
;; P-MERGE
L1AE2: DEFB $0B ; Class-0B - Offset address converted to tape
; command.
;; P-BEEP
L1AE3: DEFB $08 ; Class-08 - Two comma-separated numeric
; expressions required.
DEFB $00 ; Class-00 - No further operands.
DEFW L03F8 ; Address: $03F8; Address: BEEP
;; P-CIRCLE
L1AE7: DEFB $09 ; Class-09 - Two comma-separated numeric
; expressions required with optional colour
; items.
DEFB $05 ; Class-05 - Variable syntax checked
; by routine.
DEFW L2320 ; Address: $2320; Address: CIRCLE
;; P-INK
L1AEB: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-PAPER
L1AEC: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-FLASH
L1AED: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-BRIGHT
L1AEE: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-INVERSE
L1AEF: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-OVER
L1AF0: DEFB $07 ; Class-07 - Offset address is converted to
; colour code.
;; P-OUT
L1AF1: DEFB $08 ; Class-08 - Two comma-separated numeric
; expressions required.
DEFB $00 ; Class-00 - No further operands.
DEFW L1E7A ; Address: $1E7A; Address: OUT
;; P-BORDER
L1AF5: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L2294 ; Address: $2294; Address: BORDER
;; P-DEF-FN
L1AF9: DEFB $05 ; Class-05 - Variable syntax checked entirely
; by routine.
DEFW L1F60 ; Address: $1F60; Address: DEF-FN
;; P-OPEN
L1AFC: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $2C ; Separator: ',' see Footnote *
DEFB $0A ; Class-0A - A string expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1736 ; Address: $1736; Address: OPEN
;; P-CLOSE
L1B02: DEFB $06 ; Class-06 - A numeric expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L16E5 ; Address: $16E5; Address: CLOSE
;; P-FORMAT
L1B06: DEFB $0A ; Class-0A - A string expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1793 ; Address: $1793; Address: CAT-ETC
;; P-MOVE
L1B0A: DEFB $0A ; Class-0A - A string expression must follow.
DEFB $2C ; Separator: ','
DEFB $0A ; Class-0A - A string expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1793 ; Address: $1793; Address: CAT-ETC
;; P-ERASE
L1B10: DEFB $0A ; Class-0A - A string expression must follow.
DEFB $00 ; Class-00 - No further operands.
DEFW L1793 ; Address: $1793; Address: CAT-ETC
;; P-CAT
L1B14: DEFB $00 ; Class-00 - No further operands.
DEFW L1793 ; Address: $1793; Address: CAT-ETC
; * Note that a comma is required as a separator with the OPEN command
; but the Interface 1 programmers relaxed this allowing ';' as an
; alternative for their channels creating a confusing mixture of
; allowable syntax as it is this ROM which opens or re-opens the
; normal channels.
; -------------------------------
; Main parser (BASIC interpreter)
; -------------------------------
; This routine is called once from MAIN-2 when the BASIC line is to
; be entered or re-entered into the Program area and the syntax
; requires checking.
;; LINE-SCAN
L1B17: RES 7,(IY+$01) ; update FLAGS - signal checking syntax
CALL L19FB ; routine E-LINE-NO >>
; fetches the line number if in range.
XOR A ; clear the accumulator.
LD ($5C47),A ; set statement number SUBPPC to zero.
DEC A ; set accumulator to $FF.
LD ($5C3A),A ; set ERR_NR to 'OK' - 1.
JR L1B29 ; forward to continue at STMT-L-1.
; --------------
; Statement loop
; --------------
;
;
;; STMT-LOOP
L1B28: RST 20H ; NEXT-CHAR
; -> the entry point from above or LINE-RUN
;; STMT-L-1
L1B29: CALL L16BF ; routine SET-WORK clears workspace etc.
INC (IY+$0D) ; increment statement number SUBPPC
JP M,L1C8A ; to REPORT-C to raise
; 'Nonsense in BASIC' if over 127.
RST 18H ; GET-CHAR
LD B,$00 ; set B to zero for later indexing.
; early so any other reason ???
CP $0D ; is character carriage return ?
; i.e. an empty statement.
JR Z,L1BB3 ; forward to LINE-END if so.
CP $3A ; is it statement end marker ':' ?
; i.e. another type of empty statement.
JR Z,L1B28 ; back to STMT-LOOP if so.
LD HL,L1B76 ; address: STMT-RET
PUSH HL ; is now pushed as a return address
LD C,A ; transfer the current character to C.
; advance CH_ADD to a position after command and test if it is a command.
RST 20H ; NEXT-CHAR to advance pointer
LD A,C ; restore current character
SUB $CE ; subtract 'DEF FN' - first command
JP C,L1C8A ; jump to REPORT-C if less than a command
; raising
; 'Nonsense in BASIC'
LD C,A ; put the valid command code back in C.
; register B is zero.
LD HL,L1A48 ; address: offst-tbl
ADD HL,BC ; index into table with one of 50 commands.
LD C,(HL) ; pick up displacement to syntax table entry.
ADD HL,BC ; add to address the relevant entry.
JR L1B55 ; forward to continue at GET-PARAM
; ----------------------
; The main scanning loop
; ----------------------
; not documented properly
;
;; SCAN-LOOP
L1B52: LD HL,($5C74) ; fetch temporary address from T_ADDR
; during subsequent loops.
; -> the initial entry point with HL addressing start of syntax table entry.
;; GET-PARAM
L1B55: LD A,(HL) ; pick up the parameter.
INC HL ; address next one.
LD ($5C74),HL ; save pointer in system variable T_ADDR
LD BC,L1B52 ; address: SCAN-LOOP
PUSH BC ; is now pushed on stack as looping address.
LD C,A ; store parameter in C.
CP $20 ; is it greater than ' ' ?
JR NC,L1B6F ; forward to SEPARATOR to check that correct
; separator appears in statement if so.
LD HL,L1C01 ; address: class-tbl.
LD B,$00 ; prepare to index into the class table.
ADD HL,BC ; index to find displacement to routine.
LD C,(HL) ; displacement to BC
ADD HL,BC ; add to address the CLASS routine.
PUSH HL ; push the address on the stack.
RST 18H ; GET-CHAR - HL points to place in statement.
DEC B ; reset the zero flag - the initial state
; for all class routines.
RET ; and make an indirect jump to routine
; and then SCAN-LOOP (also on stack).
; Note. one of the class routines will eventually drop the return address
; off the stack breaking out of the above seemingly endless loop.
; -----------------------
; THE 'SEPARATOR' ROUTINE
; -----------------------
; This routine is called once to verify that the mandatory separator
; present in the parameter table is also present in the correct
; location following the command. For example, the 'THEN' token after
; the 'IF' token and expression.
;; SEPARATOR
L1B6F: RST 18H ; GET-CHAR
CP C ; does it match the character in C ?
JP NZ,L1C8A ; jump forward to REPORT-C if not
; 'Nonsense in BASIC'.
RST 20H ; NEXT-CHAR advance to next character
RET ; return.
; ------------------------------
; Come here after interpretation
; ------------------------------
;
;
;; STMT-RET
L1B76: CALL L1F54 ; routine BREAK-KEY is tested after every
; statement.
JR C,L1B7D ; step forward to STMT-R-1 if not pressed.
;; REPORT-L
L1B7B: RST 08H ; ERROR-1
DEFB $14 ; Error Report: BREAK into program
;; STMT-R-1
L1B7D: BIT 7,(IY+$0A) ; test NSPPC - will be set if $FF -
; no jump to be made.
JR NZ,L1BF4 ; forward to STMT-NEXT if a program line.
LD HL,($5C42) ; fetch line number from NEWPPC
BIT 7,H ; will be set if minus two - direct command(s)
JR Z,L1B9E ; forward to LINE-NEW if a jump is to be
; made to a new program line/statement.
; --------------------
; Run a direct command
; --------------------
; A direct command is to be run or, if continuing from above,
; the next statement of a direct command is to be considered.
;; LINE-RUN
L1B8A: LD HL,$FFFE ; The dummy value minus two
LD ($5C45),HL ; is set/reset as line number in PPC.
LD HL,($5C61) ; point to end of line + 1 - WORKSP.
DEC HL ; now point to $80 end-marker.
LD DE,($5C59) ; address the start of line E_LINE.
DEC DE ; now location before - for GET-CHAR.
LD A,($5C44) ; load statement to A from NSPPC.
JR L1BD1 ; forward to NEXT-LINE.
; ------------------------------
; Find start address of new line
; ------------------------------
; The branch was to here if a jump is to made to a new line number
; and statement.
; That is the previous statement was a GO TO, GO SUB, RUN, RETURN, NEXT etc..
;; LINE-NEW
L1B9E: CALL L196E ; routine LINE-ADDR gets address of line
; returning zero flag set if line found.
LD A,($5C44) ; fetch new statement from NSPPC
JR Z,L1BBF ; forward to LINE-USE if line matched.
; continue as must be a direct command.
AND A ; test statement which should be zero
JR NZ,L1BEC ; forward to REPORT-N if not.
; 'Statement lost'
;
LD B,A ; save statement in B.??
LD A,(HL) ; fetch high byte of line number.
AND $C0 ; test if using direct command
; a program line is less than $3F
LD A,B ; retrieve statement.
; (we can assume it is zero).
JR Z,L1BBF ; forward to LINE-USE if was a program line
; Alternatively a direct statement has finished correctly.
;; REPORT-0
L1BB0: RST 08H ; ERROR-1
DEFB $FF ; Error Report: OK
; -----------------
; THE 'REM' COMMAND
; -----------------
; The REM command routine.
; The return address STMT-RET is dropped and the rest of line ignored.
;; REM
L1BB2: POP BC ; drop return address STMT-RET and
; continue ignoring rest of line.
; ------------
; End of line?
; ------------
;
;
;; LINE-END
L1BB3: CALL L2530 ; routine SYNTAX-Z (UNSTACK-Z?)
RET Z ; return if checking syntax.
LD HL,($5C55) ; fetch NXTLIN to HL.
LD A,$C0 ; test against the
AND (HL) ; system limit $3F.
RET NZ ; return if more as must be
; end of program.
; (or direct command)
XOR A ; set statement to zero.
; and continue to set up the next following line and then consider this new one.
; ---------------------
; General line checking
; ---------------------
; The branch was here from LINE-NEW if BASIC is branching.
; or a continuation from above if dealing with a new sequential line.
; First make statement zero number one leaving others unaffected.
;; LINE-USE
L1BBF: CP $01 ; will set carry if zero.
ADC A,$00 ; add in any carry.
LD D,(HL) ; high byte of line number to D.
INC HL ; advance pointer.
LD E,(HL) ; low byte of line number to E.
LD ($5C45),DE ; set system variable PPC.
INC HL ; advance pointer.
LD E,(HL) ; low byte of line length to E.
INC HL ; advance pointer.
LD D,(HL) ; high byte of line length to D.
EX DE,HL ; swap pointer to DE before
ADD HL,DE ; adding to address the end of line.
INC HL ; advance to start of next line.
; -----------------------------
; Update NEXT LINE but consider
; previous line or edit line.
; -----------------------------
; The pointer will be the next line if continuing from above or to
; edit line end-marker ($80) if from LINE-RUN.
;; NEXT-LINE
L1BD1: LD ($5C55),HL ; store pointer in system variable NXTLIN
EX DE,HL ; bring back pointer to previous or edit line
LD ($5C5D),HL ; and update CH_ADD with character address.
LD D,A ; store statement in D.
LD E,$00 ; set E to zero to suppress token searching
; if EACH-STMT is to be called.
LD (IY+$0A),$FF ; set statement NSPPC to $FF signalling
; no jump to be made.
DEC D ; decrement and test statement
LD (IY+$0D),D ; set SUBPPC to decremented statement number.
JP Z,L1B28 ; to STMT-LOOP if result zero as statement is
; at start of line and address is known.
INC D ; else restore statement.
CALL L198B ; routine EACH-STMT finds the D'th statement
; address as E does not contain a token.
JR Z,L1BF4 ; forward to STMT-NEXT if address found.
;; REPORT-N
L1BEC: RST 08H ; ERROR-1
DEFB $16 ; Error Report: Statement lost
; -----------------
; End of statement?
; -----------------
; This combination of routines is called from 20 places when
; the end of a statement should have been reached and all preceding
; syntax is in order.
;; CHECK-END
L1BEE: CALL L2530 ; routine SYNTAX-Z
RET NZ ; return immediately in runtime
POP BC ; drop address of calling routine.
POP BC ; drop address STMT-RET.
; and continue to find next statement.
; --------------------
; Go to next statement
; --------------------
; Acceptable characters at this point are carriage return and ':'.
; If so go to next statement which in the first case will be on next line.
;; STMT-NEXT
L1BF4: RST 18H ; GET-CHAR - ignoring white space etc.
CP $0D ; is it carriage return ?
JR Z,L1BB3 ; back to LINE-END if so.
CP $3A ; is it ':' ?
JP Z,L1B28 ; jump back to STMT-LOOP to consider
; further statements
JP L1C8A ; jump to REPORT-C with any other character
; 'Nonsense in BASIC'.
; Note. the two-byte sequence 'rst 08; defb $0b' could replace the above jp.
; -------------------
; Command class table
; -------------------
;
;; class-tbl
L1C01: DEFB L1C10 - $ ; 0F offset to Address: CLASS-00
DEFB L1C1F - $ ; 1D offset to Address: CLASS-01
DEFB L1C4E - $ ; 4B offset to Address: CLASS-02
DEFB L1C0D - $ ; 09 offset to Address: CLASS-03
DEFB L1C6C - $ ; 67 offset to Address: CLASS-04
DEFB L1C11 - $ ; 0B offset to Address: CLASS-05
DEFB L1C82 - $ ; 7B offset to Address: CLASS-06
DEFB L1C96 - $ ; 8E offset to Address: CLASS-07
DEFB L1C7A - $ ; 71 offset to Address: CLASS-08
DEFB L1CBE - $ ; B4 offset to Address: CLASS-09
DEFB L1C8C - $ ; 81 offset to Address: CLASS-0A
DEFB L1CDB - $ ; CF offset to Address: CLASS-0B
; --------------------------------
; Command classes---00, 03, and 05
; --------------------------------
; class-03 e.g. RUN or RUN 200 ; optional operand
; class-00 e.g. CONTINUE ; no operand
; class-05 e.g. PRINT ; variable syntax checked by routine
;; CLASS-03
L1C0D: CALL L1CDE ; routine FETCH-NUM
;; CLASS-00
L1C10: CP A ; reset zero flag.
; if entering here then all class routines are entered with zero reset.
;; CLASS-05
L1C11: POP BC ; drop address SCAN-LOOP.
CALL Z,L1BEE ; if zero set then call routine CHECK-END >>>
; as should be no further characters.
EX DE,HL ; save HL to DE.
LD HL,($5C74) ; fetch T_ADDR
LD C,(HL) ; fetch low byte of routine
INC HL ; address next.
LD B,(HL) ; fetch high byte of routine.
EX DE,HL ; restore HL from DE
PUSH BC ; push the address
RET ; and make an indirect jump to the command.
; --------------------------------
; Command classes---01, 02, and 04
; --------------------------------
; class-01 e.g. LET A = 2*3 ; a variable is reqd
; This class routine is also called from INPUT and READ to find the
; destination variable for an assignment.
;; CLASS-01
L1C1F: CALL L28B2 ; routine LOOK-VARS returns carry set if not
; found in runtime.
; ----------------------
; Variable in assignment
; ----------------------
;
;
;; VAR-A-1
L1C22: LD (IY+$37),$00 ; set FLAGX to zero
JR NC,L1C30 ; forward to VAR-A-2 if found or checking
; syntax.
SET 1,(IY+$37) ; FLAGX - Signal a new variable
JR NZ,L1C46 ; to VAR-A-3 if not assigning to an array
; e.g. LET a$(3,3) = "X"
;; REPORT-2
L1C2E: RST 08H ; ERROR-1
DEFB $01 ; Error Report: Variable not found
;; VAR-A-2
L1C30: CALL Z,L2996 ; routine STK-VAR considers a subscript/slice
BIT 6,(IY+$01) ; test FLAGS - Numeric or string result ?
JR NZ,L1C46 ; to VAR-A-3 if numeric
XOR A ; default to array/slice - to be retained.
CALL L2530 ; routine SYNTAX-Z
CALL NZ,L2BF1 ; routine STK-FETCH is called in runtime
; may overwrite A with 1.
LD HL,$5C71 ; address system variable FLAGX
OR (HL) ; set bit 0 if simple variable to be reclaimed
LD (HL),A ; update FLAGX
EX DE,HL ; start of string/subscript to DE
;; VAR-A-3
L1C46: LD ($5C72),BC ; update STRLEN
LD ($5C4D),HL ; and DEST of assigned string.
RET ; return.
; -------------------------------------------------
; class-02 e.g. LET a = 1 + 1 ; an expression must follow
;; CLASS-02
L1C4E: POP BC ; drop return address SCAN-LOOP
CALL L1C56 ; routine VAL-FET-1 is called to check
; expression and assign result in runtime
CALL L1BEE ; routine CHECK-END checks nothing else
; is present in statement.
RET ; Return
; -------------
; Fetch a value
; -------------
;
;
;; VAL-FET-1
L1C56: LD A,($5C3B) ; initial FLAGS to A
;; VAL-FET-2
L1C59: PUSH AF ; save A briefly
CALL L24FB ; routine SCANNING evaluates expression.
POP AF ; restore A
LD D,(IY+$01) ; post-SCANNING FLAGS to D
XOR D ; xor the two sets of flags
AND $40 ; pick up bit 6 of xored FLAGS should be zero
JR NZ,L1C8A ; forward to REPORT-C if not zero
; 'Nonsense in BASIC' - results don't agree.
BIT 7,D ; test FLAGS - is syntax being checked ?
JP NZ,L2AFF ; jump forward to LET to make the assignment
; in runtime.
RET ; but return from here if checking syntax.
; ------------------
; Command class---04
; ------------------
; class-04 e.g. FOR i ; a single character variable must follow
;; CLASS-04
L1C6C: CALL L28B2 ; routine LOOK-VARS
PUSH AF ; preserve flags.
LD A,C ; fetch type - should be 011xxxxx
OR $9F ; combine with 10011111.
INC A ; test if now $FF by incrementing.
JR NZ,L1C8A ; forward to REPORT-C if result not zero.
POP AF ; else restore flags.
JR L1C22 ; back to VAR-A-1
; --------------------------------
; Expect numeric/string expression
; --------------------------------
; This routine is used to get the two coordinates of STRING$, ATTR and POINT.
; It is also called from PRINT-ITEM to get the two numeric expressions that
; follow the AT ( in PRINT AT, INPUT AT).
;; NEXT-2NUM
L1C79: RST 20H ; NEXT-CHAR advance past 'AT' or '('.
; --------
; class-08 e.g. POKE 65535,2 ; two numeric expressions separated by comma
;; CLASS-08
;; EXPT-2NUM
L1C7A: CALL L1C82 ; routine EXPT-1NUM is called for first
; numeric expression
CP $2C ; is character ',' ?
JR NZ,L1C8A ; to REPORT-C if not required separator.
; 'Nonsense in BASIC'.
RST 20H ; NEXT-CHAR
; ->
; class-06 e.g. GOTO a*1000 ; a numeric expression must follow
;; CLASS-06
;; EXPT-1NUM
L1C82: CALL L24FB ; routine SCANNING
BIT 6,(IY+$01) ; test FLAGS - Numeric or string result ?
RET NZ ; return if result is numeric.
;; REPORT-C
L1C8A: RST 08H ; ERROR-1
DEFB $0B ; Error Report: Nonsense in BASIC
; ---------------------------------------------------------------
; class-0A e.g. ERASE "????" ; a string expression must follow.
; ; these only occur in unimplemented commands
; ; although the routine expt-exp is called
; ; from SAVE-ETC
;; CLASS-0A
;; EXPT-EXP
L1C8C: CALL L24FB ; routine SCANNING
BIT 6,(IY+$01) ; test FLAGS - Numeric or string result ?
RET Z ; return if string result.
JR L1C8A ; back to REPORT-C if numeric.
; ---------------------
; Set permanent colours
; class 07
; ---------------------
; class-07 e.g. PAPER 6 ; a single class for a collection of
; ; similar commands. Clever.
;
; Note. these commands should ensure that current channel is 'S'
;; CLASS-07
L1C96: BIT 7,(IY+$01) ; test FLAGS - checking syntax only ?
; Note. there is a subroutine to do this.
RES 0,(IY+$02) ; update TV_FLAG - signal main screen in use
CALL NZ,L0D4D ; routine TEMPS is called in runtime.
POP AF ; drop return address SCAN-LOOP
LD A,($5C74) ; T_ADDR_lo to accumulator.
; points to '$07' entry + 1
; e.g. for INK points to $EC now
; Note if you move alter the syntax table next line may have to be altered.
; Note. For ZASM assembler replace following expression with SUB $13.
L1CA5: SUB L1AEB-$D8 % 256 ; convert $EB to $D8 ('INK') etc.
; ( is SUB $13 in standard ROM )
CALL L21FC ; routine CO-TEMP-4
CALL L1BEE ; routine CHECK-END check that nothing else
; in statement.
; return here in runtime.
LD HL,($5C8F) ; pick up ATTR_T and MASK_T
LD ($5C8D),HL ; and store in ATTR_P and MASK_P
LD HL,$5C91 ; point to P_FLAG.
LD A,(HL) ; pick up in A
RLCA ; rotate to left
XOR (HL) ; combine with HL
AND $AA ; 10101010
XOR (HL) ; only permanent bits affected
LD (HL),A ; reload into P_FLAG.
RET ; return.
; ------------------
; Command class---09
; ------------------
; e.g. PLOT PAPER 0; 128,88 ; two coordinates preceded by optional
; ; embedded colour items.
;
; Note. this command should ensure that current channel is actually 'S'.
;; CLASS-09
L1CBE: CALL L2530 ; routine SYNTAX-Z
JR Z,L1CD6 ; forward to CL-09-1 if checking syntax.
RES 0,(IY+$02) ; update TV_FLAG - signal main screen in use
CALL L0D4D ; routine TEMPS is called.
LD HL,$5C90 ; point to MASK_T
LD A,(HL) ; fetch mask to accumulator.
OR $F8 ; or with 11111000 paper/bright/flash 8
LD (HL),A ; mask back to MASK_T system variable.
RES 6,(IY+$57) ; reset P_FLAG - signal NOT PAPER 9 ?
RST 18H ; GET-CHAR
;; CL-09-1
L1CD6: CALL L21E2 ; routine CO-TEMP-2 deals with any embedded
; colour items.
JR L1C7A ; exit via EXPT-2NUM to check for x,y.
; Note. if either of the numeric expressions contain STR$ then the flag setting
; above will be undone when the channel flags are reset during STR$.
; e.g.
; 10 BORDER 3 : PLOT VAL STR$ 128, VAL STR$ 100
; credit John Elliott.
; ------------------
; Command class---0B
; ------------------
; Again a single class for four commands.
; This command just jumps back to SAVE-ETC to handle the four tape commands.
; The routine itself works out which command has called it by examining the
; address in T_ADDR_lo. Note therefore that the syntax table has to be
; located where these and other sequential command addresses are not split
; over a page boundary.
;; CLASS-0B
L1CDB: JP L0605 ; jump way back to SAVE-ETC
; --------------
; Fetch a number
; --------------
; This routine is called from CLASS-03 when a command may be followed by
; an optional numeric expression e.g. RUN. If the end of statement has
; been reached then zero is used as the default.
; Also called from LIST-4.
;; FETCH-NUM
L1CDE: CP $0D ; is character a carriage return ?
JR Z,L1CE6 ; forward to USE-ZERO if so
CP $3A ; is it ':' ?
JR NZ,L1C82 ; forward to EXPT-1NUM if not.
; else continue and use zero.
; ----------------
; Use zero routine
; ----------------
; This routine is called four times to place the value zero on the
; calculator stack as a default value in runtime.
;; USE-ZERO
L1CE6: CALL L2530 ; routine SYNTAX-Z (UNSTACK-Z?)
RET Z ;
RST 28H ;; FP-CALC
DEFB $A0 ;;stk-zero ;0.
DEFB $38 ;;end-calc
RET ; return.
; -------------------
; Handle STOP command
; -------------------
; Command Syntax: STOP
; One of the shortest and least used commands. As with 'OK' not an error.
;; REPORT-9
;; STOP
L1CEE: RST 08H ; ERROR-1
DEFB $08 ; Error Report: STOP statement
; -----------------
; Handle IF command
; -----------------
; e.g. IF score>100 THEN PRINT "You Win"
; The parser has already checked the expression the result of which is on
; the calculator stack. The presence of the 'THEN' separator has also been
; checked and CH-ADD points to the command after THEN.
;
;; IF
L1CF0: POP BC ; drop return address - STMT-RET
CALL L2530 ; routine SYNTAX-Z
JR Z,L1D00 ; forward to IF-1 if checking syntax
; to check syntax of PRINT "You Win"
RST 28H ;; FP-CALC score>100 (1=TRUE 0=FALSE)
DEFB $02 ;;delete .
DEFB $38 ;;end-calc
EX DE,HL ; make HL point to deleted value
CALL L34E9 ; routine TEST-ZERO
JP C,L1BB3 ; jump to LINE-END if FALSE (0)
;; IF-1
L1D00: JP L1B29 ; to STMT-L-1, if true (1) to execute command
; after 'THEN' token.
; ------------------
; Handle FOR command
; ------------------
; e.g. FOR i = 0 TO 1 STEP 0.1
; Using the syntax tables, the parser has already checked for a start and
; limit value and also for the intervening separator.
; the two values v,l are on the calculator stack.
; CLASS-04 has also checked the variable and the name is in STRLEN_lo.
; The routine begins by checking for an optional STEP.
;; FOR
L1D03: CP $CD ; is there a 'STEP' ?
JR NZ,L1D10 ; to F-USE-1 if not to use 1 as default.
RST 20H ; NEXT-CHAR
CALL L1C82 ; routine EXPT-1NUM
CALL L1BEE ; routine CHECK-END
JR L1D16 ; to F-REORDER
; ---
;; F-USE-1
L1D10: CALL L1BEE ; routine CHECK-END
RST 28H ;; FP-CALC v,l.
DEFB $A1 ;;stk-one v,l,1=s.
DEFB $38 ;;end-calc
;; F-REORDER
L1D16: RST 28H ;; FP-CALC v,l,s.
DEFB $C0 ;;st-mem-0 v,l,s.
DEFB $02 ;;delete v,l.
DEFB $01 ;;exchange l,v.
DEFB $E0 ;;get-mem-0 l,v,s.
DEFB $01 ;;exchange l,s,v.
DEFB $38 ;;end-calc
CALL L2AFF ; routine LET assigns the initial value v to
; the variable altering type if necessary.
LD ($5C68),HL ; The system variable MEM is made to point to
; the variable instead of its normal
; location MEMBOT
DEC HL ; point to single-character name
LD A,(HL) ; fetch name
SET 7,(HL) ; set bit 7 at location
LD BC,$0006 ; add six to HL
ADD HL,BC ; to address where limit should be.
RLCA ; test bit 7 of original name.
JR C,L1D34 ; forward to F-L-S if already a FOR/NEXT
; variable
LD C,$0D ; otherwise an additional 13 bytes are needed.
; 5 for each value, two for line number and
; 1 byte for looping statement.
CALL L1655 ; routine MAKE-ROOM creates them.
INC HL ; make HL address limit.
;; F-L-S
L1D34: PUSH HL ; save position.
RST 28H ;; FP-CALC l,s.
DEFB $02 ;;delete l.
DEFB $02 ;;delete .
DEFB $38 ;;end-calc
; DE points to STKEND, l.
POP HL ; restore variable position
EX DE,HL ; swap pointers
LD C,$0A ; ten bytes to move
LDIR ; Copy 'deleted' values to variable.
LD HL,($5C45) ; Load with current line number from PPC
EX DE,HL ; exchange pointers.
LD (HL),E ; save the looping line
INC HL ; in the next
LD (HL),D ; two locations.
LD D,(IY+$0D) ; fetch statement from SUBPPC system variable.
INC D ; increment statement.
INC HL ; and pointer
LD (HL),D ; and store the looping statement.
;
CALL L1DDA ; routine NEXT-LOOP considers an initial
RET NC ; iteration. Return to STMT-RET if a loop is
; possible to execute next statement.
; no loop is possible so execution continues after the matching 'NEXT'
LD B,(IY+$38) ; get single-character name from STRLEN_lo
LD HL,($5C45) ; get the current line from PPC
LD ($5C42),HL ; and store it in NEWPPC
LD A,($5C47) ; fetch current statement from SUBPPC
NEG ; Negate as counter decrements from zero
; initially and we are in the middle of a
; line.
LD D,A ; Store result in D.
LD HL,($5C5D) ; get current address from CH_ADD
LD E,$F3 ; search will be for token 'NEXT'
;; F-LOOP
L1D64: PUSH BC ; save variable name.
LD BC,($5C55) ; fetch NXTLIN
CALL L1D86 ; routine LOOK-PROG searches for 'NEXT' token.
LD ($5C55),BC ; update NXTLIN
POP BC ; and fetch the letter
JR C,L1D84 ; forward to REPORT-I if the end of program
; was reached by LOOK-PROG.
; 'FOR without NEXT'
RST 20H ; NEXT-CHAR fetches character after NEXT
OR $20 ; ensure it is upper-case.
CP B ; compare with FOR variable name
JR Z,L1D7C ; forward to F-FOUND if it matches.
; but if no match i.e. nested FOR/NEXT loops then continue search.
RST 20H ; NEXT-CHAR
JR L1D64 ; back to F-LOOP
; ---
;; F-FOUND
L1D7C: RST 20H ; NEXT-CHAR
LD A,$01 ; subtract the negated counter from 1
SUB D ; to give the statement after the NEXT
LD ($5C44),A ; set system variable NSPPC
RET ; return to STMT-RET to branch to new
; line and statement. ->
; ---
;; REPORT-I
L1D84: RST 08H ; ERROR-1
DEFB $11 ; Error Report: FOR without NEXT
; ---------
; LOOK-PROG
; ---------
; Find DATA, DEF FN or NEXT.
; This routine searches the program area for one of the above three keywords.
; On entry, HL points to start of search area.
; The token is in E, and D holds a statement count, decremented from zero.
;; LOOK-PROG
L1D86: LD A,(HL) ; fetch current character
CP $3A ; is it ':' a statement separator ?
JR Z,L1DA3 ; forward to LOOK-P-2 if so.
; The starting point was PROG - 1 or the end of a line.
;; LOOK-P-1
L1D8B: INC HL ; increment pointer to address
LD A,(HL) ; the high byte of line number
AND $C0 ; test for program end marker $80 or a
; variable
SCF ; Set Carry Flag
RET NZ ; return with carry set if at end
; of program. ->
LD B,(HL) ; high byte of line number to B
INC HL ;
LD C,(HL) ; low byte to C.
LD ($5C42),BC ; set system variable NEWPPC.
INC HL ;
LD C,(HL) ; low byte of line length to C.
INC HL ;
LD B,(HL) ; high byte to B.
PUSH HL ; save address
ADD HL,BC ; add length to position.
LD B,H ; and save result
LD C,L ; in BC.
POP HL ; restore address.
LD D,$00 ; initialize statement counter to zero.
;; LOOK-P-2
L1DA3: PUSH BC ; save address of next line
CALL L198B ; routine EACH-STMT searches current line.
POP BC ; restore address.
RET NC ; return if match was found. ->
JR L1D8B ; back to LOOK-P-1 for next line.
; -------------------
; Handle NEXT command
; -------------------
; e.g. NEXT i
; The parameter tables have already evaluated the presence of a variable
;; NEXT
L1DAB: BIT 1,(IY+$37) ; test FLAGX - handling a new variable ?
JP NZ,L1C2E ; jump back to REPORT-2 if so
; 'Variable not found'
; now test if found variable is a simple variable uninitialized by a FOR.
LD HL,($5C4D) ; load address of variable from DEST
BIT 7,(HL) ; is it correct type ?
JR Z,L1DD8 ; forward to REPORT-1 if not
; 'NEXT without FOR'
INC HL ; step past variable name
LD ($5C68),HL ; and set MEM to point to three 5-byte values
; value, limit, step.
RST 28H ;; FP-CALC add step and re-store
DEFB $E0 ;;get-mem-0 v.
DEFB $E2 ;;get-mem-2 v,s.
DEFB $0F ;;addition v+s.
DEFB $C0 ;;st-mem-0 v+s.
DEFB $02 ;;delete .
DEFB $38 ;;end-calc
CALL L1DDA ; routine NEXT-LOOP tests against limit.
RET C ; return if no more iterations possible.
LD HL,($5C68) ; find start of variable contents from MEM.
LD DE,$000F ; add 3*5 to
ADD HL,DE ; address the looping line number
LD E,(HL) ; low byte to E
INC HL ;
LD D,(HL) ; high byte to D
INC HL ; address looping statement
LD H,(HL) ; and store in H
EX DE,HL ; swap registers
JP L1E73 ; exit via GO-TO-2 to execute another loop.
; ---
;; REPORT-1
L1DD8: RST 08H ; ERROR-1
DEFB $00 ; Error Report: NEXT without FOR
; -----------------
; Perform NEXT loop
; -----------------
; This routine is called from the FOR command to test for an initial
; iteration and from the NEXT command to test for all subsequent iterations.
; the system variable MEM addresses the variable's contents which, in the
; latter case, have had the step, possibly negative, added to the value.
;; NEXT-LOOP
L1DDA: RST 28H ;; FP-CALC
DEFB $E1 ;;get-mem-1 l.
DEFB $E0 ;;get-mem-0 l,v.
DEFB $E2 ;;get-mem-2 l,v,s.
DEFB $36 ;;less-0 l,v,(1/0) negative step ?
DEFB $00 ;;jump-true l,v.(1/0)
DEFB $02 ;;to L1DE2, NEXT-1 if step negative
DEFB $01 ;;exchange v,l.
;; NEXT-1
L1DE2: DEFB $03 ;;subtract l-v OR v-l.
DEFB $37 ;;greater-0 (1/0)
DEFB $00 ;;jump-true .
DEFB $04 ;;to L1DE9, NEXT-2 if no more iterations.
DEFB $38 ;;end-calc .
AND A ; clear carry flag signalling another loop.
RET ; return
; ---
;; NEXT-2
L1DE9: DEFB $38 ;;end-calc .
SCF ; set carry flag signalling looping exhausted.
RET ; return
; -------------------
; Handle READ command
; -------------------
; e.g. READ a, b$, c$(1000 TO 3000)
; A list of comma-separated variables is assigned from a list of
; comma-separated expressions.
; As it moves along the first list, the character address CH_ADD is stored
; in X_PTR while CH_ADD is used to read the second list.
;; READ-3
L1DEC: RST 20H ; NEXT-CHAR
; -> Entry point.
;; READ
L1DED: CALL L1C1F ; routine CLASS-01 checks variable.
CALL L2530 ; routine SYNTAX-Z
JR Z,L1E1E ; forward to READ-2 if checking syntax
RST 18H ; GET-CHAR
LD ($5C5F),HL ; save character position in X_PTR.
LD HL,($5C57) ; load HL with Data Address DATADD, which is
; the start of the program or the address
; after the last expression that was read or
; the address of the line number of the
; last RESTORE command.
LD A,(HL) ; fetch character
CP $2C ; is it a comma ?
JR Z,L1E0A ; forward to READ-1 if so.
; else all data in this statement has been read so look for next DATA token
LD E,$E4 ; token 'DATA'
CALL L1D86 ; routine LOOK-PROG
JR NC,L1E0A ; forward to READ-1 if DATA found
; else report the error.
;; REPORT-E
L1E08: RST 08H ; ERROR-1
DEFB $0D ; Error Report: Out of DATA
;; READ-1
L1E0A: CALL L0077 ; routine TEMP-PTR1 advances updating CH_ADD
; with new DATADD position.
CALL L1C56 ; routine VAL-FET-1 assigns value to variable
; checking type match and adjusting CH_ADD.
RST 18H ; GET-CHAR fetches adjusted character position
LD ($5C57),HL ; store back in DATADD
LD HL,($5C5F) ; fetch X_PTR the original READ CH_ADD
LD (IY+$26),$00 ; now nullify X_PTR_hi
CALL L0078 ; routine TEMP-PTR2 restores READ CH_ADD
;; READ-2
L1E1E: RST 18H ; GET-CHAR
CP $2C ; is it ',' indicating more variables to read ?
JR Z,L1DEC ; back to READ-3 if so
CALL L1BEE ; routine CHECK-END
RET ; return from here in runtime to STMT-RET.
; -------------------
; Handle DATA command
; -------------------
; In runtime this 'command' is passed by but the syntax is checked when such
; a statement is found while parsing a line.
; e.g. DATA 1, 2, "text", score-1, a$(location, room, object), FN r(49),
; wages - tax, TRUE, The meaning of life
;; DATA
L1E27: CALL L2530 ; routine SYNTAX-Z to check status
JR NZ,L1E37 ; forward to DATA-2 if in runtime
;; DATA-1
L1E2C: CALL L24FB ; routine SCANNING to check syntax of
; expression
CP $2C ; is it a comma ?
CALL NZ,L1BEE ; routine CHECK-END checks that statement
; is complete. Will make an early exit if
; so. >>>
RST 20H ; NEXT-CHAR
JR L1E2C ; back to DATA-1
; ---
;; DATA-2
L1E37: LD A,$E4 ; set token to 'DATA' and continue into
; the PASS-BY routine.
; ----------------------------------
; Check statement for DATA or DEF FN
; ----------------------------------
; This routine is used to backtrack to a command token and then
; forward to the next statement in runtime.
;; PASS-BY
L1E39: LD B,A ; Give BC enough space to find token.
CPDR ; Compare decrement and repeat. (Only use).
; Work backwards till keyword is found which
; is start of statement before any quotes.
; HL points to location before keyword.
LD DE,$0200 ; count 1+1 statements, dummy value in E to
; inhibit searching for a token.
JP L198B ; to EACH-STMT to find next statement
; -----------------------------------------------------------------------
; A General Note on Invalid Line Numbers.
; =======================================
; One of the revolutionary concepts of Sinclair BASIC was that it supported
; virtual line numbers. That is the destination of a GO TO, RESTORE etc. need
; not exist. It could be a point before or after an actual line number.
; Zero suffices for a before but the after should logically be infinity.
; Since the maximum actual line limit is 9999 then the system limit, 16383
; when variables kick in, would serve fine as a virtual end point.
; However, ironically, only the LOAD command gets it right. It will not
; autostart a program that has been saved with a line higher than 16383.
; All the other commands deal with the limit unsatisfactorily.
; LIST, RUN, GO TO, GO SUB and RESTORE have problems and the latter may
; crash the machine when supplied with an inappropriate virtual line number.
; This is puzzling as very careful consideration must have been given to
; this point when the new variable types were allocated their masks and also
; when the routine NEXT-ONE was successfully re-written to reflect this.
; An enigma.
; -------------------------------------------------------------------------
; ----------------------
; Handle RESTORE command
; ----------------------
; The restore command sets the system variable for the data address to
; point to the location before the supplied line number or first line
; thereafter.
; This alters the position where subsequent READ commands look for data.
; Note. If supplied with inappropriate high numbers the system may crash
; in the LINE-ADDR routine as it will pass the program/variables end-marker
; and then lose control of what it is looking for - variable or line number.
; - observation, Steven Vickers, 1984, Pitman.
;; RESTORE
L1E42: CALL L1E99 ; routine FIND-INT2 puts integer in BC.
; Note. B should be checked against limit $3F
; and an error generated if higher.
; this entry point is used from RUN command with BC holding zero
;; REST-RUN
L1E45: LD H,B ; transfer the line
LD L,C ; number to the HL register.
CALL L196E ; routine LINE-ADDR to fetch the address.
DEC HL ; point to the location before the line.
LD ($5C57),HL ; update system variable DATADD.
RET ; return to STMT-RET (or RUN)
; ------------------------
; Handle RANDOMIZE command
; ------------------------
; This command sets the SEED for the RND function to a fixed value.
; With the parameter zero, a random start point is used depending on
; how long the computer has been switched on.
;; RANDOMIZE
L1E4F: CALL L1E99 ; routine FIND-INT2 puts parameter in BC.
LD A,B ; test this
OR C ; for zero.
JR NZ,L1E5A ; forward to RAND-1 if not zero.
LD BC,($5C78) ; use the lower two bytes at FRAMES1.
;; RAND-1
L1E5A: LD ($5C76),BC ; place in SEED system variable.
RET ; return to STMT-RET
; -----------------------
; Handle CONTINUE command
; -----------------------
; The CONTINUE command transfers the OLD (but incremented) values of
; line number and statement to the equivalent "NEW VALUE" system variables
; by using the last part of GO TO and exits indirectly to STMT-RET.
;; CONTINUE
L1E5F: LD HL,($5C6E) ; fetch OLDPPC line number.
LD D,(IY+$36) ; fetch OSPPC statement.
JR L1E73 ; forward to GO-TO-2
; --------------------
; Handle GO TO command
; --------------------
; The GO TO command routine is also called by GO SUB and RUN routines
; to evaluate the parameters of both commands.
; It updates the system variables used to fetch the next line/statement.
; It is at STMT-RET that the actual change in control takes place.
; Unlike some BASICs the line number need not exist.
; Note. the high byte of the line number is incorrectly compared with $F0
; instead of $3F. This leads to commands with operands greater than 32767
; being considered as having been run from the editing area and the
; error report 'Statement Lost' is given instead of 'OK'.
; - Steven Vickers, 1984.
;; GO-TO
L1E67: CALL L1E99 ; routine FIND-INT2 puts operand in BC
LD H,B ; transfer line
LD L,C ; number to HL.
LD D,$00 ; set statement to 0 - first.
LD A,H ; compare high byte only
CP $F0 ; to $F0 i.e. 61439 in full.
JR NC,L1E9F ; forward to REPORT-B if above.
; This call entry point is used to update the system variables e.g. by RETURN.
;; GO-TO-2
L1E73: LD ($5C42),HL ; save line number in NEWPPC
LD (IY+$0A),D ; and statement in NSPPC
RET ; to STMT-RET (or GO-SUB command)
; ------------------
; Handle OUT command
; ------------------
; Syntax has been checked and the two comma-separated values are on the
; calculator stack.
;; OUT
L1E7A: CALL L1E85 ; routine TWO-PARAM fetches values
; to BC and A.
OUT (C),A ; perform the operation.
RET ; return to STMT-RET.
; -------------------
; Handle POKE command
; -------------------
; This routine alters a single byte in the 64K address space.
; Happily no check is made as to whether ROM or RAM is addressed.
; Sinclair BASIC requires no poking of system variables.
;; POKE
L1E80: CALL L1E85 ; routine TWO-PARAM fetches values
; to BC and A.
LD (BC),A ; load memory location with A.
RET ; return to STMT-RET.
; ------------------------------------
; Fetch two parameters from calculator stack
; ------------------------------------
; This routine fetches a byte and word from the calculator stack
; producing an error if either is out of range.
;; TWO-PARAM
L1E85: CALL L2DD5 ; routine FP-TO-A
JR C,L1E9F ; forward to REPORT-B if overflow occurred
JR Z,L1E8E ; forward to TWO-P-1 if positive
NEG ; negative numbers are made positive
;; TWO-P-1
L1E8E: PUSH AF ; save the value
CALL L1E99 ; routine FIND-INT2 gets integer to BC
POP AF ; restore the value
RET ; return
; -------------
; Find integers
; -------------
; The first of these routines fetches a 8-bit integer (range 0-255) from the
; calculator stack to the accumulator and is used for colours, streams,
; durations and coordinates.
; The second routine fetches 16-bit integers to the BC register pair
; and is used to fetch command and function arguments involving line numbers
; or memory addresses and also array subscripts and tab arguments.
; ->
;; FIND-INT1
L1E94: CALL L2DD5 ; routine FP-TO-A
JR L1E9C ; forward to FIND-I-1 for common exit routine.
; ---
; ->
;; FIND-INT2
L1E99: CALL L2DA2 ; routine FP-TO-BC
;; FIND-I-1
L1E9C: JR C,L1E9F ; to REPORT-Bb with overflow.
RET Z ; return if positive.
;; REPORT-Bb
L1E9F: RST 08H ; ERROR-1
DEFB $0A ; Error Report: Integer out of range
; ------------------
; Handle RUN command
; ------------------
; This command runs a program starting at an optional line.
; It performs a 'RESTORE 0' then CLEAR
;; RUN
L1EA1: CALL L1E67 ; routine GO-TO puts line number in
; system variables.
LD BC,$0000 ; prepare to set DATADD to first line.
CALL L1E45 ; routine REST-RUN does the 'restore'.
; Note BC still holds zero.
JR L1EAF ; forward to CLEAR-RUN to clear variables
; without disturbing RAMTOP and
; exit indirectly to STMT-RET
; --------------------
; Handle CLEAR command
; --------------------
; This command reclaims the space used by the variables.
; It also clears the screen and the GO SUB stack.
; With an integer expression, it sets the uppermost memory
; address within the BASIC system.
; "Contrary to the manual, CLEAR doesn't execute a RESTORE" -
; Steven Vickers, Pitman Pocket Guide to the Spectrum, 1984.
;; CLEAR
L1EAC: CALL L1E99 ; routine FIND-INT2 fetches to BC.
;; CLEAR-RUN
L1EAF: LD A,B ; test for
OR C ; zero.
JR NZ,L1EB7 ; skip to CLEAR-1 if not zero.
LD BC,($5CB2) ; use the existing value of RAMTOP if zero.
;; CLEAR-1
L1EB7: PUSH BC ; save ramtop value.
LD DE,($5C4B) ; fetch VARS
LD HL,($5C59) ; fetch E_LINE
DEC HL ; adjust to point at variables end-marker.
CALL L19E5 ; routine RECLAIM-1 reclaims the space used by
; the variables.
CALL L0D6B ; routine CLS to clear screen.
LD HL,($5C65) ; fetch STKEND the start of free memory.
LD DE,$0032 ; allow for another 50 bytes.
ADD HL,DE ; add the overhead to HL.
POP DE ; restore the ramtop value.
SBC HL,DE ; if HL is greater than the value then jump
JR NC,L1EDA ; forward to REPORT-M
; 'RAMTOP no good'
LD HL,($5CB4) ; now P-RAMT ($7FFF on 16K RAM machine)
AND A ; exact this time.
SBC HL,DE ; new ramtop must be lower or the same.
JR NC,L1EDC ; skip to CLEAR-2 if in actual RAM.
;; REPORT-M
L1EDA: RST 08H ; ERROR-1
DEFB $15 ; Error Report: RAMTOP no good
;; CLEAR-2
L1EDC: EX DE,HL ; transfer ramtop value to HL.
LD ($5CB2),HL ; update system variable RAMTOP.
POP DE ; pop the return address STMT-RET.
POP BC ; pop the Error Address.
LD (HL),$3E ; now put the GO SUB end-marker at RAMTOP.
DEC HL ; leave a location beneath it.
LD SP,HL ; initialize the machine stack pointer.
PUSH BC ; push the error address.
LD ($5C3D),SP ; make ERR_SP point to location.
EX DE,HL ; put STMT-RET in HL.
JP (HL) ; and go there directly.
; ---------------------
; Handle GO SUB command
; ---------------------
; The GO SUB command diverts BASIC control to a new line number
; in a very similar manner to GO TO but
; the current line number and current statement + 1
; are placed on the GO SUB stack as a RETURN point.
;; GO-SUB
L1EED: POP DE ; drop the address STMT-RET
LD H,(IY+$0D) ; fetch statement from SUBPPC and
INC H ; increment it
EX (SP),HL ; swap - error address to HL,
; H (statement) at top of stack,
; L (unimportant) beneath.
INC SP ; adjust to overwrite unimportant byte
LD BC,($5C45) ; fetch the current line number from PPC
PUSH BC ; and PUSH onto GO SUB stack.
; the empty machine-stack can be rebuilt
PUSH HL ; push the error address.
LD ($5C3D),SP ; make system variable ERR_SP point to it.
PUSH DE ; push the address STMT-RET.
CALL L1E67 ; call routine GO-TO to update the system
; variables NEWPPC and NSPPC.
; then make an indirect exit to STMT-RET via
LD BC,$0014 ; a 20-byte overhead memory check.
; ----------------------
; Check available memory
; ----------------------
; This routine is used on many occasions when extending a dynamic area
; upwards or the GO SUB stack downwards.
;; TEST-ROOM
L1F05: LD HL,($5C65) ; fetch STKEND
ADD HL,BC ; add the supplied test value
JR C,L1F15 ; forward to REPORT-4 if over $FFFF
EX DE,HL ; was less so transfer to DE
LD HL,$0050 ; test against another 80 bytes
ADD HL,DE ; anyway
JR C,L1F15 ; forward to REPORT-4 if this passes $FFFF
SBC HL,SP ; if less than the machine stack pointer
RET C ; then return - OK.
;; REPORT-4
L1F15: LD L,$03 ; prepare 'Out of Memory'
JP L0055 ; jump back to ERROR-3 at $0055
; Note. this error can't be trapped at $0008
; ------------------------------
; THE 'FREE MEMORY' USER ROUTINE
; ------------------------------
; This routine is not used by the ROM but allows users to evaluate
; approximate free memory with PRINT 65536 - USR 7962.
;; free-mem
L1F1A: LD BC,$0000 ; allow no overhead.
CALL L1F05 ; routine TEST-ROOM.
LD B,H ; transfer the result
LD C,L ; to the BC register.
RET ; the USR function returns value of BC.
; --------------------
; THE 'RETURN' COMMAND
; --------------------
; As with any command, there are two values on the machine stack at the time
; it is invoked. The machine stack is below the GOSUB stack. Both grow
; downwards, the machine stack by two bytes, the GOSUB stack by 3 bytes.
; The highest location is a statement byte followed by a two-byte line number.
;; RETURN
L1F23: POP BC ; drop the address STMT-RET.
POP HL ; now the error address.
POP DE ; now a possible BASIC return line.
LD A,D ; the high byte $00 - $27 is
CP $3E ; compared with the traditional end-marker $3E.
JR Z,L1F36 ; forward to REPORT-7 with a match.
; 'RETURN without GOSUB'
; It was not the end-marker so a single statement byte remains at the base of
; the calculator stack. It can't be popped off.
DEC SP ; adjust stack pointer to create room for two
; bytes.
EX (SP),HL ; statement to H, error address to base of
; new machine stack.
EX DE,HL ; statement to D, BASIC line number to HL.
LD ($5C3D),SP ; adjust ERR_SP to point to new stack pointer
PUSH BC ; now re-stack the address STMT-RET
JP L1E73 ; to GO-TO-2 to update statement and line
; system variables and exit indirectly to the
; address just pushed on stack.
; ---
;; REPORT-7
L1F36: PUSH DE ; replace the end-marker.
PUSH HL ; now restore the error address
; as will be required in a few clock cycles.
RST 08H ; ERROR-1
DEFB $06 ; Error Report: RETURN without GOSUB
; --------------------
; Handle PAUSE command
; --------------------
; The pause command takes as its parameter the number of interrupts
; for which to wait. PAUSE 50 pauses for about a second.
; PAUSE 0 pauses indefinitely.
; Both forms can be finished by pressing a key.
;; PAUSE
L1F3A: CALL L1E99 ; routine FIND-INT2 puts value in BC
;; PAUSE-1
L1F3D: HALT ; wait for interrupt.
DEC BC ; decrease counter.
LD A,B ; test if
OR C ; result is zero.
JR Z,L1F4F ; forward to PAUSE-END if so.
LD A,B ; test if
AND C ; now $FFFF
INC A ; that is, initially zero.
JR NZ,L1F49 ; skip forward to PAUSE-2 if not.
INC BC ; restore counter to zero.
;; PAUSE-2
L1F49: BIT 5,(IY+$01) ; test FLAGS - has a new key been pressed ?
JR Z,L1F3D ; back to PAUSE-1 if not.
;; PAUSE-END
L1F4F: RES 5,(IY+$01) ; update FLAGS - signal no new key
RET ; and return.
; -------------------
; Check for BREAK key
; -------------------
; This routine is called from COPY-LINE, when interrupts are disabled,
; to test if BREAK (SHIFT - SPACE) is being pressed.
; It is also called at STMT-RET after every statement.
;; BREAK-KEY
L1F54: LD A,$7F ; Input address: $7FFE
IN A,($FE) ; read lower right keys
RRA ; rotate bit 0 - SPACE
RET C ; return if not reset
LD A,$FE ; Input address: $FEFE
IN A,($FE) ; read lower left keys
RRA ; rotate bit 0 - SHIFT
RET ; carry will be set if not pressed.
; return with no carry if both keys
; pressed.
; ---------------------
; Handle DEF FN command
; ---------------------
; e.g. DEF FN r$(a$,a) = a$(a TO )
; this 'command' is ignored in runtime but has its syntax checked
; during line-entry.
;; DEF-FN
L1F60: CALL L2530 ; routine SYNTAX-Z
JR Z,L1F6A ; forward to DEF-FN-1 if parsing
LD A,$CE ; else load A with 'DEF FN' and
JP L1E39 ; jump back to PASS-BY
; ---
; continue here if checking syntax.
;; DEF-FN-1
L1F6A: SET 6,(IY+$01) ; set FLAGS - Assume numeric result
CALL L2C8D ; call routine ALPHA
JR NC,L1F89 ; if not then to DEF-FN-4 to jump to
; 'Nonsense in BASIC'
RST 20H ; NEXT-CHAR
CP $24 ; is it '$' ?
JR NZ,L1F7D ; to DEF-FN-2 if not as numeric.
RES 6,(IY+$01) ; set FLAGS - Signal string result
RST 20H ; get NEXT-CHAR
;; DEF-FN-2
L1F7D: CP $28 ; is it '(' ?
JR NZ,L1FBD ; to DEF-FN-7 'Nonsense in BASIC'
RST 20H ; NEXT-CHAR
CP $29 ; is it ')' ?
JR Z,L1FA6 ; to DEF-FN-6 if null argument
;; DEF-FN-3
L1F86: CALL L2C8D ; routine ALPHA checks that it is the expected
; alphabetic character.
;; DEF-FN-4
L1F89: JP NC,L1C8A ; to REPORT-C if not
; 'Nonsense in BASIC'.
EX DE,HL ; save pointer in DE
RST 20H ; NEXT-CHAR re-initializes HL from CH_ADD
; and advances.
CP $24 ; '$' ? is it a string argument.
JR NZ,L1F94 ; forward to DEF-FN-5 if not.
EX DE,HL ; save pointer to '$' in DE
RST 20H ; NEXT-CHAR re-initializes HL and advances
;; DEF-FN-5
L1F94: EX DE,HL ; bring back pointer.
LD BC,$0006 ; the function requires six hidden bytes for
; each parameter passed.
; The first byte will be $0E
; then 5-byte numeric value
; or 5-byte string pointer.
CALL L1655 ; routine MAKE-ROOM creates space in program
; area.
INC HL ; adjust HL (set by LDDR)
INC HL ; to point to first location.
LD (HL),$0E ; insert the 'hidden' marker.
; Note. these invisible storage locations hold nothing meaningful for the
; moment. They will be used every time the corresponding function is
; evaluated in runtime.
; Now consider the following character fetched earlier.
CP $2C ; is it ',' ? (more than one parameter)
JR NZ,L1FA6 ; to DEF-FN-6 if not
RST 20H ; else NEXT-CHAR
JR L1F86 ; and back to DEF-FN-3
; ---
;; DEF-FN-6
L1FA6: CP $29 ; should close with a ')'
JR NZ,L1FBD ; to DEF-FN-7 if not
; 'Nonsense in BASIC'
RST 20H ; get NEXT-CHAR
CP $3D ; is it '=' ?
JR NZ,L1FBD ; to DEF-FN-7 if not 'Nonsense...'
RST 20H ; address NEXT-CHAR
LD A,($5C3B) ; get FLAGS which has been set above
PUSH AF ; and preserve
CALL L24FB ; routine SCANNING checks syntax of expression
; and also sets flags.
POP AF ; restore previous flags
XOR (IY+$01) ; xor with FLAGS - bit 6 should be same
; therefore will be reset.
AND $40 ; isolate bit 6.
;; DEF-FN-7
L1FBD: JP NZ,L1C8A ; jump back to REPORT-C if the expected result
; is not the same type.
; 'Nonsense in BASIC'
CALL L1BEE ; routine CHECK-END will return early if
; at end of statement and move onto next
; else produce error report. >>>
; There will be no return to here.
; -------------------------------
; Returning early from subroutine
; -------------------------------
; All routines are capable of being run in two modes - syntax checking mode
; and runtime mode. This routine is called often to allow a routine to return
; early if checking syntax.
;; UNSTACK-Z
L1FC3: CALL L2530 ; routine SYNTAX-Z sets zero flag if syntax
; is being checked.
POP HL ; drop the return address.
RET Z ; return to previous call in chain if checking
; syntax.
JP (HL) ; jump to return address as BASIC program is
; actually running.
; ---------------------
; Handle LPRINT command
; ---------------------
; A simple form of 'PRINT #3' although it can output to 16 streams.
; Probably for compatibility with other BASICs particularly ZX81 BASIC.
; An extra UDG might have been better.
;; LPRINT
L1FC9: LD A,$03 ; the printer channel
JR L1FCF ; forward to PRINT-1
; ---------------------
; Handle PRINT commands
; ---------------------
; The Spectrum's main stream output command.
; The default stream is stream 2 which is normally the upper screen
; of the computer. However the stream can be altered in range 0 - 15.
;; PRINT
L1FCD: LD A,$02 ; the stream for the upper screen.
; The LPRINT command joins here.
;; PRINT-1
L1FCF: CALL L2530 ; routine SYNTAX-Z checks if program running
CALL NZ,L1601 ; routine CHAN-OPEN if so
CALL L0D4D ; routine TEMPS sets temporary colours.
CALL L1FDF ; routine PRINT-2 - the actual item
CALL L1BEE ; routine CHECK-END gives error if not at end
; of statement
RET ; and return >>>
; ------------------------------------
; this subroutine is called from above
; and also from INPUT.
;; PRINT-2
L1FDF: RST 18H ; GET-CHAR gets printable character
CALL L2045 ; routine PR-END-Z checks if more printing
JR Z,L1FF2 ; to PRINT-4 if not e.g. just 'PRINT :'
; This tight loop deals with combinations of positional controls and
; print items. An early return can be made from within the loop
; if the end of a print sequence is reached.
;; PRINT-3
L1FE5: CALL L204E ; routine PR-POSN-1 returns zero if more
; but returns early at this point if
; at end of statement!
;
JR Z,L1FE5 ; to PRINT-3 if consecutive positioners
CALL L1FFC ; routine PR-ITEM-1 deals with strings etc.
CALL L204E ; routine PR-POSN-1 for more position codes
JR Z,L1FE5 ; loop back to PRINT-3 if so
;; PRINT-4
L1FF2: CP $29 ; return now if this is ')' from input-item.
; (see INPUT.)
RET Z ; or continue and print carriage return in
; runtime
; ---------------------
; Print carriage return
; ---------------------
; This routine which continues from above prints a carriage return
; in run-time. It is also called once from PRINT-POSN.
;; PRINT-CR
L1FF5: CALL L1FC3 ; routine UNSTACK-Z
LD A,$0D ; prepare a carriage return
RST 10H ; PRINT-A
RET ; return
; -----------
; Print items
; -----------
; This routine deals with print items as in
; PRINT AT 10,0;"The value of A is ";a
; It returns once a single item has been dealt with as it is part
; of a tight loop that considers sequences of positional and print items
;; PR-ITEM-1
L1FFC: RST 18H ; GET-CHAR
CP $AC ; is character 'AT' ?
JR NZ,L200E ; forward to PR-ITEM-2 if not.
CALL L1C79 ; routine NEXT-2NUM check for two comma
; separated numbers placing them on the
; calculator stack in runtime.
CALL L1FC3 ; routine UNSTACK-Z quits if checking syntax.
CALL L2307 ; routine STK-TO-BC get the numbers in B and C.
LD A,$16 ; prepare the 'at' control.
JR L201E ; forward to PR-AT-TAB to print the sequence.
; ---
;; PR-ITEM-2
L200E: CP $AD ; is character 'TAB' ?
JR NZ,L2024 ; to PR-ITEM-3 if not
RST 20H ; NEXT-CHAR to address next character
CALL L1C82 ; routine EXPT-1NUM
CALL L1FC3 ; routine UNSTACK-Z quits if checking syntax.
CALL L1E99 ; routine FIND-INT2 puts integer in BC.
LD A,$17 ; prepare the 'tab' control.
;; PR-AT-TAB
L201E: RST 10H ; PRINT-A outputs the control
LD A,C ; first value to A
RST 10H ; PRINT-A outputs it.
LD A,B ; second value
RST 10H ; PRINT-A
RET ; return - item finished >>>
; ---
; Now consider paper 2; #2; a$
;; PR-ITEM-3
L2024: CALL L21F2 ; routine CO-TEMP-3 will print any colour
RET NC ; items - return if success.
CALL L2070 ; routine STR-ALTER considers new stream
RET NC ; return if altered.
CALL L24FB ; routine SCANNING now to evaluate expression
CALL L1FC3 ; routine UNSTACK-Z if not runtime.
BIT 6,(IY+$01) ; test FLAGS - Numeric or string result ?
CALL Z,L2BF1 ; routine STK-FETCH if string.
; note no flags affected.
JP NZ,L2DE3 ; to PRINT-FP to print if numeric >>>
; It was a string expression - start in DE, length in BC
; Now enter a loop to print it
;; PR-STRING
L203C: LD A,B ; this tests if the
OR C ; length is zero and sets flag accordingly.
DEC BC ; this doesn't but decrements counter.
RET Z ; return if zero.
LD A,(DE) ; fetch character.
INC DE ; address next location.
RST 10H ; PRINT-A.
JR L203C ; loop back to PR-STRING.
; ---------------
; End of printing
; ---------------
; This subroutine returns zero if no further printing is required
; in the current statement.
; The first terminator is found in escaped input items only,
; the others in print_items.
;; PR-END-Z
L2045: CP $29 ; is character a ')' ?
RET Z ; return if so - e.g. INPUT (p$); a$
;; PR-ST-END
L2048: CP $0D ; is it a carriage return ?
RET Z ; return also - e.g. PRINT a
CP $3A ; is character a ':' ?
RET ; return - zero flag will be set if so.
; e.g. PRINT a :
; --------------
; Print position
; --------------
; This routine considers a single positional character ';', ',', '''
;; PR-POSN-1
L204E: RST 18H ; GET-CHAR
CP $3B ; is it ';' ?
; i.e. print from last position.
JR Z,L2067 ; forward to PR-POSN-3 if so.
; i.e. do nothing.
CP $2C ; is it ',' ?
; i.e. print at next tabstop.
JR NZ,L2061 ; forward to PR-POSN-2 if anything else.
CALL L2530 ; routine SYNTAX-Z
JR Z,L2067 ; forward to PR-POSN-3 if checking syntax.
LD A,$06 ; prepare the 'comma' control character.
RST 10H ; PRINT-A outputs to current channel in
; run-time.
JR L2067 ; skip to PR-POSN-3.
; ---
; check for newline.
;; PR-POSN-2
L2061: CP $27 ; is character a "'" ? (newline)
RET NZ ; return if no match >>>
CALL L1FF5 ; routine PRINT-CR outputs a carriage return
; in runtime only.
;; PR-POSN-3
L2067: RST 20H ; NEXT-CHAR to A.
CALL L2045 ; routine PR-END-Z checks if at end.
JR NZ,L206E ; to PR-POSN-4 if not.
POP BC ; drop return address if at end.
;; PR-POSN-4
L206E: CP A ; reset the zero flag.
RET ; and return to loop or quit.
; ------------
; Alter stream
; ------------
; This routine is called from PRINT ITEMS above, and also LIST as in
; LIST #15
;; STR-ALTER
L2070: CP $23 ; is character '#' ?
SCF ; set carry flag.
RET NZ ; return if no match.
RST 20H ; NEXT-CHAR
CALL L1C82 ; routine EXPT-1NUM gets stream number
AND A ; prepare to exit early with carry reset
CALL L1FC3 ; routine UNSTACK-Z exits early if parsing
CALL L1E94 ; routine FIND-INT1 gets number off stack
CP $10 ; must be range 0 - 15 decimal.
JP NC,L160E ; jump back to REPORT-Oa if not
; 'Invalid stream'.
CALL L1601 ; routine CHAN-OPEN
AND A ; clear carry - signal item dealt with.
RET ; return
; -------------------
; THE 'INPUT' COMMAND
; -------------------
; This command is mysterious.
;
;; INPUT
L2089: CALL L2530 ; routine SYNTAX-Z to check if in runtime.
JR Z,L2096 ; forward to INPUT-1 if checking syntax.
LD A,$01 ; select channel 'K' the keyboard for input.
CALL L1601 ; routine CHAN-OPEN opens the channel and sets
; bit 0 of TV_FLAG.
; Note. As a consequence of clearing the lower screen channel 0 is made
; the current channel so the above two instructions are superfluous.
CALL L0D6E ; routine CLS-LOWER clears the lower screen
; and sets DF_SZ to two and TV_FLAG to $01.
;; INPUT-1
L2096: LD (IY+$02),$01 ; update TV_FLAG - signal lower screen in use
; ensuring that the correct set of system
; variables are updated and that the border
; colour is used.
; Note. The Complete Spectrum ROM Disassembly incorrectly names DF-SZ as the
; system variable that is updated above and if, as some have done, you make
; this unnecessary alteration then there will be two blank lines between the
; lower screen and the upper screen areas which will also scroll wrongly.
CALL L20C1 ; routine IN-ITEM-1 to handle the input.
CALL L1BEE ; routine CHECK-END will make an early exit
; if checking syntax. >>>
; Keyboard input has been made and it remains to adjust the upper
; screen in case the lower two lines have been extended upwards.
LD BC,($5C88) ; fetch S_POSN current line/column of
; the upper screen.
LD A,($5C6B) ; fetch DF_SZ the display file size of
; the lower screen.
CP B ; test that lower screen does not overlap
JR C,L20AD ; forward to INPUT-2 if not.
; the two screens overlap so adjust upper screen.
LD C,$21 ; set column of upper screen to leftmost.
LD B,A ; and line to one above lower screen.
; continue forward to update upper screen
; print position.
;; INPUT-2
L20AD: LD ($5C88),BC ; set S_POSN update upper screen line/column.
LD A,$19 ; subtract from twenty five
SUB B ; the new line number.
LD ($5C8C),A ; and place result in SCR_CT - scroll count.
RES 0,(IY+$02) ; update TV_FLAG - signal main screen in use.
CALL L0DD9 ; routine CL-SET sets the print position
; system variables for the upper screen.
JP L0D6E ; jump back to CLS-LOWER and make
; an indirect exit >>.
; ---------------------
; INPUT ITEM subroutine
; ---------------------
; This subroutine deals with the input items and print items.
; from the current input channel.
; It is only called from the above INPUT routine but was obviously
; once called from somewhere else in another context.
;; IN-ITEM-1
L20C1: CALL L204E ; routine PR-POSN-1 deals with a single
; position item at each call.
JR Z,L20C1 ; back to IN-ITEM-1 until no more in a
; sequence.
CP $28 ; is character '(' ?
JR NZ,L20D8 ; forward to IN-ITEM-2 if not.
; any variables within braces will be treated as part, or all, of the prompt
; instead of being used as destination variables.
RST 20H ; NEXT-CHAR
CALL L1FDF ; routine PRINT-2 to output the dynamic
; prompt.
RST 18H ; GET-CHAR
CP $29 ; is character a matching ')' ?
JP NZ,L1C8A ; jump back to REPORT-C if not.
; 'Nonsense in BASIC'.
RST 20H ; NEXT-CHAR
JP L21B2 ; forward to IN-NEXT-2
; ---
;; IN-ITEM-2
L20D8: CP $CA ; is the character the token 'LINE' ?
JR NZ,L20ED ; forward to IN-ITEM-3 if not.
RST 20H ; NEXT-CHAR - variable must come next.
CALL L1C1F ; routine CLASS-01 returns destination
; address of variable to be assigned.
; or generates an error if no variable
; at this position.
SET 7,(IY+$37) ; update FLAGX - signal handling INPUT LINE
BIT 6,(IY+$01) ; test FLAGS - numeric or string result ?
JP NZ,L1C8A ; jump back to REPORT-C if not string
; 'Nonsense in BASIC'.
JR L20FA ; forward to IN-PROMPT to set up workspace.
; ---
; the jump was here for other variables.
;; IN-ITEM-3
L20ED: CALL L2C8D ; routine ALPHA checks if character is
; a suitable variable name.
JP NC,L21AF ; forward to IN-NEXT-1 if not
CALL L1C1F ; routine CLASS-01 returns destination
; address of variable to be assigned.
RES 7,(IY+$37) ; update FLAGX - signal not INPUT LINE.
;; IN-PROMPT
L20FA: CALL L2530 ; routine SYNTAX-Z
JP Z,L21B2 ; forward to IN-NEXT-2 if checking syntax.
CALL L16BF ; routine SET-WORK clears workspace.
LD HL,$5C71 ; point to system variable FLAGX
RES 6,(HL) ; signal string result.
SET 5,(HL) ; signal in Input Mode for editor.
LD BC,$0001 ; initialize space required to one for
; the carriage return.
BIT 7,(HL) ; test FLAGX - INPUT LINE in use ?
JR NZ,L211C ; forward to IN-PR-2 if so as that is
; all the space that is required.
LD A,($5C3B) ; load accumulator from FLAGS
AND $40 ; mask to test BIT 6 of FLAGS and clear
; the other bits in A.
; numeric result expected ?
JR NZ,L211A ; forward to IN-PR-1 if so
LD C,$03 ; increase space to three bytes for the
; pair of surrounding quotes.
;; IN-PR-1
L211A: OR (HL) ; if numeric result, set bit 6 of FLAGX.
LD (HL),A ; and update system variable
;; IN-PR-2
L211C: RST 30H ; BC-SPACES opens 1 or 3 bytes in workspace
LD (HL),$0D ; insert carriage return at last new location.
LD A,C ; fetch the length, one or three.
RRCA ; lose bit 0.
RRCA ; test if quotes required.
JR NC,L2129 ; forward to IN-PR-3 if not.
LD A,$22 ; load the '"' character
LD (DE),A ; place quote in first new location at DE.
DEC HL ; decrease HL - from carriage return.
LD (HL),A ; and place a quote in second location.
;; IN-PR-3
L2129: LD ($5C5B),HL ; set keyboard cursor K_CUR to HL
BIT 7,(IY+$37) ; test FLAGX - is this INPUT LINE ??
JR NZ,L215E ; forward to IN-VAR-3 if so as input will
; be accepted without checking its syntax.
LD HL,($5C5D) ; fetch CH_ADD
PUSH HL ; and save on stack.
LD HL,($5C3D) ; fetch ERR_SP
PUSH HL ; and save on stack
;; IN-VAR-1
L213A: LD HL,L213A ; address: IN-VAR-1 - this address
PUSH HL ; is saved on stack to handle errors.
BIT 4,(IY+$30) ; test FLAGS2 - is K channel in use ?
JR Z,L2148 ; forward to IN-VAR-2 if not using the
; keyboard for input. (??)
LD ($5C3D),SP ; set ERR_SP to point to IN-VAR-1 on stack.
;; IN-VAR-2
L2148: LD HL,($5C61) ; set HL to WORKSP - start of workspace.
CALL L11A7 ; routine REMOVE-FP removes floating point
; forms when looping in error condition.
LD (IY+$00),$FF ; set ERR_NR to 'OK' cancelling the error.
; but X_PTR causes flashing error marker
; to be displayed at each call to the editor.
CALL L0F2C ; routine EDITOR allows input to be entered
; or corrected if this is second time around.
; if we pass to next then there are no system errors
RES 7,(IY+$01) ; update FLAGS - signal checking syntax
CALL L21B9 ; routine IN-ASSIGN checks syntax using
; the VAL-FET-2 and powerful SCANNING routines.
; any syntax error and its back to IN-VAR-1.
; but with the flashing error marker showing
; where the error is.
; Note. the syntax of string input has to be
; checked as the user may have removed the
; bounding quotes or escaped them as with
; "hat" + "stand" for example.
; proceed if syntax passed.
JR L2161 ; jump forward to IN-VAR-4
; ---
; the jump was to here when using INPUT LINE.
;; IN-VAR-3
L215E: CALL L0F2C ; routine EDITOR is called for input
; when ENTER received rejoin other route but with no syntax check.
; INPUT and INPUT LINE converge here.
;; IN-VAR-4
L2161: LD (IY+$22),$00 ; set K_CUR_hi to a low value so that the cursor
; no longer appears in the input line.
CALL L21D6 ; routine IN-CHAN-K tests if the keyboard
; is being used for input.
JR NZ,L2174 ; forward to IN-VAR-5 if using another input
; channel.
; continue here if using the keyboard.
CALL L111D ; routine ED-COPY overprints the edit line
; to the lower screen. The only visible
; affect is that the cursor disappears.
; if you're inputting more than one item in
; a statement then that becomes apparent.
LD BC,($5C82) ; fetch line and column from ECHO_E
CALL L0DD9 ; routine CL-SET sets S-POSNL to those
; values.
; if using another input channel rejoin here.
;; IN-VAR-5
L2174: LD HL,$5C71 ; point HL to FLAGX
RES 5,(HL) ; signal not in input mode
BIT 7,(HL) ; is this INPUT LINE ?
RES 7,(HL) ; cancel the bit anyway.
JR NZ,L219B ; forward to IN-VAR-6 if INPUT LINE.
POP HL ; drop the looping address
POP HL ; drop the address of previous
; error handler.
LD ($5C3D),HL ; set ERR_SP to point to it.
POP HL ; drop original CH_ADD which points to
; INPUT command in BASIC line.
LD ($5C5F),HL ; save in X_PTR while input is assigned.
SET 7,(IY+$01) ; update FLAGS - Signal running program
CALL L21B9 ; routine IN-ASSIGN is called again
; this time the variable will be assigned
; the input value without error.
; Note. the previous example now
; becomes "hatstand"
LD HL,($5C5F) ; fetch stored CH_ADD value from X_PTR.
LD (IY+$26),$00 ; set X_PTR_hi so that iy is no longer relevant.
LD ($5C5D),HL ; put restored value back in CH_ADD
JR L21B2 ; forward to IN-NEXT-2 to see if anything
; more in the INPUT list.
; ---
; the jump was to here with INPUT LINE only
;; IN-VAR-6
L219B: LD HL,($5C63) ; STKBOT points to the end of the input.
LD DE,($5C61) ; WORKSP points to the beginning.
SCF ; prepare for true subtraction.
SBC HL,DE ; subtract to get length
LD B,H ; transfer it to
LD C,L ; the BC register pair.
CALL L2AB2 ; routine STK-STO-$ stores parameters on
; the calculator stack.
CALL L2AFF ; routine LET assigns it to destination.
JR L21B2 ; forward to IN-NEXT-2 as print items
; not allowed with INPUT LINE.
; Note. that "hat" + "stand" will, for
; example, be unchanged as also would
; 'PRINT "Iris was here"'.
; ---
; the jump was to here when ALPHA found more items while looking for
; a variable name.
;; IN-NEXT-1
L21AF: CALL L1FFC ; routine PR-ITEM-1 considers further items.
;; IN-NEXT-2
L21B2: CALL L204E ; routine PR-POSN-1 handles a position item.
JP Z,L20C1 ; jump back to IN-ITEM-1 if the zero flag
; indicates more items are present.
RET ; return.
; ---------------------------
; INPUT ASSIGNMENT Subroutine
; ---------------------------
; This subroutine is called twice from the INPUT command when normal
; keyboard input is assigned. On the first occasion syntax is checked
; using SCANNING. The final call with the syntax flag reset is to make
; the assignment.
;; IN-ASSIGN
L21B9: LD HL,($5C61) ; fetch WORKSP start of input
LD ($5C5D),HL ; set CH_ADD to first character
RST 18H ; GET-CHAR ignoring leading white-space.
CP $E2 ; is it 'STOP'
JR Z,L21D0 ; forward to IN-STOP if so.
LD A,($5C71) ; load accumulator from FLAGX
CALL L1C59 ; routine VAL-FET-2 makes assignment
; or goes through the motions if checking
; syntax. SCANNING is used.
RST 18H ; GET-CHAR
CP $0D ; is it carriage return ?
RET Z ; return if so
; either syntax is OK
; or assignment has been made.
; if another character was found then raise an error.
; User doesn't see report but the flashing error marker
; appears in the lower screen.
;; REPORT-Cb
L21CE: RST 08H ; ERROR-1
DEFB $0B ; Error Report: Nonsense in BASIC
;; IN-STOP
L21D0: CALL L2530 ; routine SYNTAX-Z (UNSTACK-Z?)
RET Z ; return if checking syntax
; as user wouldn't see error report.
; but generate visible error report
; on second invocation.
;; REPORT-H
L21D4: RST 08H ; ERROR-1
DEFB $10 ; Error Report: STOP in INPUT
; -----------------------------------
; THE 'TEST FOR CHANNEL K' SUBROUTINE
; -----------------------------------
; This subroutine is called once from the keyboard INPUT command to check if
; the input routine in use is the one for the keyboard.
;; IN-CHAN-K
L21D6: LD HL,($5C51) ; fetch address of current channel CURCHL
INC HL ;
INC HL ; advance past
INC HL ; input and
INC HL ; output streams
LD A,(HL) ; fetch the channel identifier.
CP $4B ; test for 'K'
RET ; return with zero set if keyboard is use.
; --------------------
; Colour Item Routines
; --------------------
;
; These routines have 3 entry points -
; 1) CO-TEMP-2 to handle a series of embedded Graphic colour items.
; 2) CO-TEMP-3 to handle a single embedded print colour item.
; 3) CO TEMP-4 to handle a colour command such as FLASH 1
;
; "Due to a bug, if you bring in a peripheral channel and later use a colour
; statement, colour controls will be sent to it by mistake." - Steven Vickers
; Pitman Pocket Guide, 1984.
;
; To be fair, this only applies if the last channel was other than 'K', 'S'
; or 'P', which are all that are supported by this ROM, but if that last
; channel was a microdrive file, network channel etc. then
; PAPER 6; CLS will not turn the screen yellow and
; CIRCLE INK 2; 128,88,50 will not draw a red circle.
;
; This bug does not apply to embedded PRINT items as it is quite permissible
; to mix stream altering commands and colour items.
; The fix therefore would be to ensure that CLASS-07 and CLASS-09 make
; channel 'S' the current channel when not checking syntax.
; -----------------------------------------------------------------
;; CO-TEMP-1
L21E1: RST 20H ; NEXT-CHAR
; -> Entry point from CLASS-09. Embedded Graphic colour items.
; e.g. PLOT INK 2; PAPER 8; 128,88
; Loops till all colour items output, finally addressing the coordinates.
;; CO-TEMP-2
L21E2: CALL L21F2 ; routine CO-TEMP-3 to output colour control.
RET C ; return if nothing more to output. ->
RST 18H ; GET-CHAR
CP $2C ; is it ',' separator ?
JR Z,L21E1 ; back if so to CO-TEMP-1
CP $3B ; is it ';' separator ?
JR Z,L21E1 ; back to CO-TEMP-1 for more.
JP L1C8A ; to REPORT-C (REPORT-Cb is within range)
; 'Nonsense in BASIC'
; -------------------
; CO-TEMP-3
; -------------------
; -> this routine evaluates and outputs a colour control and parameter.
; It is called from above and also from PR-ITEM-3 to handle a single embedded
; print item e.g. PRINT PAPER 6; "Hi". In the latter case, the looping for
; multiple items is within the PR-ITEM routine.
; It is quite permissible to send these to any stream.
;; CO-TEMP-3
L21F2: CP $D9 ; is it 'INK' ?
RET C ; return if less.
CP $DF ; compare with 'OUT'
CCF ; Complement Carry Flag
RET C ; return if greater than 'OVER', $DE.
PUSH AF ; save the colour token.
RST 20H ; address NEXT-CHAR
POP AF ; restore token and continue.
; -> this entry point used by CLASS-07. e.g. the command PAPER 6.
;; CO-TEMP-4
L21FC: SUB $C9 ; reduce to control character $10 (INK)
; thru $15 (OVER).
PUSH AF ; save control.
CALL L1C82 ; routine EXPT-1NUM stacks addressed
; parameter on calculator stack.
POP AF ; restore control.
AND A ; clear carry
CALL L1FC3 ; routine UNSTACK-Z returns if checking syntax.
PUSH AF ; save again
CALL L1E94 ; routine FIND-INT1 fetches parameter to A.
LD D,A ; transfer now to D
POP AF ; restore control.
RST 10H ; PRINT-A outputs the control to current
; channel.
LD A,D ; transfer parameter to A.
RST 10H ; PRINT-A outputs parameter.
RET ; return. ->
; -------------------------------------------------------------------------
;
; {fl}{br}{ paper }{ ink } The temporary colour attributes
; ___ ___ ___ ___ ___ ___ ___ ___ system variable.
; ATTR_T | | | | | | | | |
; | | | | | | | | |
; 23695 |___|___|___|___|___|___|___|___|
; 7 6 5 4 3 2 1 0
;
;
; {fl}{br}{ paper }{ ink } The temporary mask used for
; ___ ___ ___ ___ ___ ___ ___ ___ transparent colours. Any bit
; MASK_T | | | | | | | | | that is 1 shows that the
; | | | | | | | | | corresponding attribute is
; 23696 |___|___|___|___|___|___|___|___| taken not from ATTR-T but from
; 7 6 5 4 3 2 1 0 what is already on the screen.
;
;
; {paper9 }{ ink9 }{ inv1 }{ over1} The print flags. Even bits are
; ___ ___ ___ ___ ___ ___ ___ ___ temporary flags. The odd bits
; P_FLAG | | | | | | | | | are the permanent flags.
; | p | t | p | t | p | t | p | t |
; 23697 |___|___|___|___|___|___|___|___|
; 7 6 5 4 3 2 1 0
;
; -----------------------------------------------------------------------
; ------------------------------------
; The colour system variable handler.
; ------------------------------------
; This is an exit branch from PO-1-OPER, PO-2-OPER
; A holds control $10 (INK) to $15 (OVER)
; D holds parameter 0-9 for ink/paper 0,1 or 8 for bright/flash,
; 0 or 1 for over/inverse.
;; CO-TEMP-5
L2211: SUB $11 ; reduce range $FF-$04
ADC A,$00 ; add in carry if INK
JR Z,L2234 ; forward to CO-TEMP-7 with INK and PAPER.
SUB $02 ; reduce range $FF-$02
ADC A,$00 ; add carry if FLASH
JR Z,L2273 ; forward to CO-TEMP-C with FLASH and BRIGHT.
CP $01 ; is it 'INVERSE' ?
LD A,D ; fetch parameter for INVERSE/OVER
LD B,$01 ; prepare OVER mask setting bit 0.
JR NZ,L2228 ; forward to CO-TEMP-6 if OVER
RLCA ; shift bit 0
RLCA ; to bit 2
LD B,$04 ; set bit 2 of mask for inverse.
;; CO-TEMP-6
L2228: LD C,A ; save the A
LD A,D ; re-fetch parameter
CP $02 ; is it less than 2
JR NC,L2244 ; to REPORT-K if not 0 or 1.
; 'Invalid colour'.
LD A,C ; restore A
LD HL,$5C91 ; address system variable P_FLAG
JR L226C ; forward to exit via routine CO-CHANGE
; ---
; the branch was here with INK/PAPER and carry set for INK.
;; CO-TEMP-7
L2234: LD A,D ; fetch parameter
LD B,$07 ; set ink mask 00000111
JR C,L223E ; forward to CO-TEMP-8 with INK
RLCA ; shift bits 0-2
RLCA ; to
RLCA ; bits 3-5
LD B,$38 ; set paper mask 00111000
; both paper and ink rejoin here
;; CO-TEMP-8
L223E: LD C,A ; value to C
LD A,D ; fetch parameter
CP $0A ; is it less than 10d ?
JR C,L2246 ; forward to CO-TEMP-9 if so.
; ink 10 etc. is not allowed.
;; REPORT-K
L2244: RST 08H ; ERROR-1
DEFB $13 ; Error Report: Invalid colour
;; CO-TEMP-9
L2246: LD HL,$5C8F ; address system variable ATTR_T initially.
CP $08 ; compare with 8
JR C,L2258 ; forward to CO-TEMP-B with 0-7.
LD A,(HL) ; fetch temporary attribute as no change.
JR Z,L2257 ; forward to CO-TEMP-A with INK/PAPER 8
; it is either ink 9 or paper 9 (contrasting)
OR B ; or with mask to make white
CPL ; make black and change other to dark
AND $24 ; 00100100
JR Z,L2257 ; forward to CO-TEMP-A if black and
; originally light.
LD A,B ; else just use the mask (white)
;; CO-TEMP-A
L2257: LD C,A ; save A in C
;; CO-TEMP-B
L2258: LD A,C ; load colour to A
CALL L226C ; routine CO-CHANGE addressing ATTR-T
LD A,$07 ; put 7 in accumulator
CP D ; compare with parameter
SBC A,A ; $00 if 0-7, $FF if 8
CALL L226C ; routine CO-CHANGE addressing MASK-T
; mask returned in A.
; now consider P-FLAG.
RLCA ; 01110000 or 00001110
RLCA ; 11100000 or 00011100
AND $50 ; 01000000 or 00010000 (AND 01010000)
LD B,A ; transfer to mask
LD A,$08 ; load A with 8
CP D ; compare with parameter
SBC A,A ; $FF if was 9, $00 if 0-8
; continue while addressing P-FLAG
; setting bit 4 if ink 9
; setting bit 6 if paper 9
; -----------------------
; Handle change of colour
; -----------------------
; This routine addresses a system variable ATTR_T, MASK_T or P-FLAG in HL.
; colour value in A, mask in B.
;; CO-CHANGE
L226C: XOR (HL) ; impress bits specified
AND B ; by mask
XOR (HL) ; on system variable.
LD (HL),A ; update system variable.
INC HL ; address next location.
LD A,B ; put current value of mask in A
RET ; return.
; ---
; the branch was here with flash and bright
;; CO-TEMP-C
L2273: SBC A,A ; set zero flag for bright.
LD A,D ; fetch original parameter 0,1 or 8
RRCA ; rotate bit 0 to bit 7
LD B,$80 ; mask for flash 10000000
JR NZ,L227D ; forward to CO-TEMP-D if flash
RRCA ; rotate bit 7 to bit 6
LD B,$40 ; mask for bright 01000000
;; CO-TEMP-D
L227D: LD C,A ; store value in C
LD A,D ; fetch parameter
CP $08 ; compare with 8
JR Z,L2287 ; forward to CO-TEMP-E if 8
CP $02 ; test if 0 or 1
JR NC,L2244 ; back to REPORT-K if not
; 'Invalid colour'
;; CO-TEMP-E
L2287: LD A,C ; value to A
LD HL,$5C8F ; address ATTR_T
CALL L226C ; routine CO-CHANGE addressing ATTR_T
LD A,C ; fetch value
RRCA ; for flash8/bright8 complete
RRCA ; rotations to put set bit in
RRCA ; bit 7 (flash) bit 6 (bright)
JR L226C ; back to CO-CHANGE addressing MASK_T
; and indirect return.
; ---------------------
; Handle BORDER command
; ---------------------
; Command syntax example: BORDER 7
; This command routine sets the border to one of the eight colours.
; The colours used for the lower screen are based on this.
;; BORDER
L2294: CALL L1E94 ; routine FIND-INT1
CP $08 ; must be in range 0 (black) to 7 (white)
JR NC,L2244 ; back to REPORT-K if not
; 'Invalid colour'.
OUT ($FE),A ; outputting to port effects an immediate
; change.
RLCA ; shift the colour to
RLCA ; the paper bits setting the
RLCA ; ink colour black.
BIT 5,A ; is the number light coloured ?
; i.e. in the range green to white.
JR NZ,L22A6 ; skip to BORDER-1 if so
XOR $07 ; make the ink white.
;; BORDER-1
L22A6: LD ($5C48),A ; update BORDCR with new paper/ink
RET ; return.
; -----------------
; Get pixel address
; -----------------
;
;
;; PIXEL-ADD
L22AA: LD A,$AF ; load with 175 decimal.
SUB B ; subtract the y value.
JP C,L24F9 ; jump forward to REPORT-Bc if greater.
; 'Integer out of range'
; the high byte is derived from Y only.
; the first 3 bits are always 010
; the next 2 bits denote in which third of the screen the byte is.
; the last 3 bits denote in which of the 8 scan lines within a third
; the byte is located. There are 24 discrete values.
LD B,A ; the line number from top of screen to B.
AND A ; clear carry (already clear)
RRA ; 0xxxxxxx
SCF ; set carry flag
RRA ; 10xxxxxx
AND A ; clear carry flag
RRA ; 010xxxxx
XOR B ;
AND $F8 ; keep the top 5 bits 11111000
XOR B ; 010xxbbb
LD H,A ; transfer high byte to H.
; the low byte is derived from both X and Y.
LD A,C ; the x value 0-255.
RLCA ;
RLCA ;
RLCA ;
XOR B ; the y value
AND $C7 ; apply mask 11000111
XOR B ; restore unmasked bits xxyyyxxx
RLCA ; rotate to xyyyxxxx
RLCA ; required position. yyyxxxxx
LD L,A ; low byte to L.
; finally form the pixel position in A.
LD A,C ; x value to A
AND $07 ; mod 8
RET ; return
; ----------------
; Point Subroutine
; ----------------
; The point subroutine is called from s-point via the scanning functions
; table.
;; POINT-SUB
L22CB: CALL L2307 ; routine STK-TO-BC
CALL L22AA ; routine PIXEL-ADD finds address of pixel.
LD B,A ; pixel position to B, 0-7.
INC B ; increment to give rotation count 1-8.
LD A,(HL) ; fetch byte from screen.
;; POINT-LP
L22D4: RLCA ; rotate and loop back
DJNZ L22D4 ; to POINT-LP until pixel at right.
AND $01 ; test to give zero or one.
JP L2D28 ; jump forward to STACK-A to save result.
; -------------------
; Handle PLOT command
; -------------------
; Command Syntax example: PLOT 128,88
;
;; PLOT
L22DC: CALL L2307 ; routine STK-TO-BC
CALL L22E5 ; routine PLOT-SUB
JP L0D4D ; to TEMPS
; -------------------
; The Plot subroutine
; -------------------
; A screen byte holds 8 pixels so it is necessary to rotate a mask
; into the correct position to leave the other 7 pixels unaffected.
; However all 64 pixels in the character cell take any embedded colour
; items.
; A pixel can be reset (inverse 1), toggled (over 1), or set ( with inverse
; and over switches off). With both switches on, the byte is simply put
; back on the screen though the colours may change.
;; PLOT-SUB
L22E5: LD ($5C7D),BC ; store new x/y values in COORDS
CALL L22AA ; routine PIXEL-ADD gets address in HL,
; count from left 0-7 in B.
LD B,A ; transfer count to B.
INC B ; increase 1-8.
LD A,$FE ; 11111110 in A.
;; PLOT-LOOP
L22F0: RRCA ; rotate mask.
DJNZ L22F0 ; to PLOT-LOOP until B circular rotations.
LD B,A ; load mask to B
LD A,(HL) ; fetch screen byte to A
LD C,(IY+$57) ; P_FLAG to C
BIT 0,C ; is it to be OVER 1 ?
JR NZ,L22FD ; forward to PL-TST-IN if so.
; was over 0
AND B ; combine with mask to blank pixel.
;; PL-TST-IN
L22FD: BIT 2,C ; is it inverse 1 ?
JR NZ,L2303 ; to PLOT-END if so.
XOR B ; switch the pixel
CPL ; restore other 7 bits
;; PLOT-END
L2303: LD (HL),A ; load byte to the screen.
JP L0BDB ; exit to PO-ATTR to set colours for cell.
; ------------------------------
; Put two numbers in BC register
; ------------------------------
;
;
;; STK-TO-BC
L2307: CALL L2314 ; routine STK-TO-A
LD B,A ;
PUSH BC ;
CALL L2314 ; routine STK-TO-A
LD E,C ;
POP BC ;
LD D,C ;
LD C,A ;
RET ;
; -----------------------
; Put stack in A register
; -----------------------
; This routine puts the last value on the calculator stack into the accumulator
; deleting the last value.
;; STK-TO-A
L2314: CALL L2DD5 ; routine FP-TO-A compresses last value into
; accumulator. e.g. PI would become 3.
; zero flag set if positive.
JP C,L24F9 ; jump forward to REPORT-Bc if >= 255.5.
LD C,$01 ; prepare a positive sign byte.
RET Z ; return if FP-TO-BC indicated positive.
LD C,$FF ; prepare negative sign byte and
RET ; return.
; --------------------
; THE 'CIRCLE' COMMAND
; --------------------
; "Goe not Thou about to Square eyther circle" -
; - John Donne, Cambridge educated theologian, 1624
;
; The CIRCLE command draws a circle as a series of straight lines.
; In some ways it can be regarded as a polygon, but the first line is drawn
; as a tangent, taking the radius as its distance from the centre.
;
; Both the CIRCLE algorithm and the ARC drawing algorithm make use of the
; 'ROTATION FORMULA' (see later). It is only necessary to work out where
; the first line will be drawn and how long it is and then the rotation
; formula takes over and calculates all other rotated points.
;
; All Spectrum circles consist of two vertical lines at each side and two
; horizontal lines at the top and bottom. The number of lines is calculated
; from the radius of the circle and is always divisible by 4. For complete
; circles it will range from 4 for a square circle to 32 for a circle of
; radius 87. The Spectrum can attempt larger circles e.g. CIRCLE 0,14,255
; but these will error as they go off-screen after four lines are drawn.
; At the opposite end, CIRCLE 128,88,1.23 will draw a circle as a perfect 3x3
; square using 4 straight lines although very small circles are just drawn as
; a dot on the screen.
;
; The first chord drawn is the vertical chord on the right of the circle.
; The starting point is at the base of this chord which is drawn upwards and
; the circle continues in an anti-clockwise direction. As noted earlier the
; x-coordinate of this point measured from the centre of the circle is the
; radius.
;
; The CIRCLE command makes extensive use of the calculator and as part of
; process of drawing a large circle, free memory is checked 1315 times.
; When drawing a large arc, free memory is checked 928 times.
; A single call to 'sin' involves 63 memory checks and so values of sine
; and cosine are pre-calculated and held in the mem locations. As a
; clever trick 'cos' is derived from 'sin' using simple arithmetic operations
; instead of the more expensive 'cos' function.
;
; Initially, the syntax has been partly checked using the class for the DRAW
; command which stacks the origin of the circle (X,Y).
;; CIRCLE
L2320: RST 18H ; GET-CHAR x, y.
CP $2C ; Is character the required comma ?
JP NZ,L1C8A ; Jump, if not, to REPORT-C
; 'Nonsense in basic'
RST 20H ; NEXT-CHAR advances the parsed character address.
CALL L1C82 ; routine EXPT-1NUM stacks radius in runtime.
CALL L1BEE ; routine CHECK-END will return here in runtime
; if nothing follows the command.
; Now make the radius positive and ensure that it is in floating point form
; so that the exponent byte can be accessed for quick testing.
RST 28H ;; FP-CALC x, y, r.
DEFB $2A ;;abs x, y, r.
DEFB $3D ;;re-stack x, y, r.
DEFB $38 ;;end-calc x, y, r.
LD A,(HL) ; Fetch first, floating-point, exponent byte.
CP $81 ; Compare to one.
JR NC,L233B ; Forward to C-R-GRE-1
; if circle radius is greater than one.
; The circle is no larger than a single pixel so delete the radius from the
; calculator stack and plot a point at the centre.
RST 28H ;; FP-CALC x, y, r.
DEFB $02 ;;delete x, y.
DEFB $38 ;;end-calc x, y.
JR L22DC ; back to PLOT routine to just plot x,y.
; ---
; Continue when the circle's radius measures greater than one by forming
; the angle 2 * PI radians which is 360 degrees.
;; C-R-GRE-1
L233B: RST 28H ;; FP-CALC x, y, r
DEFB $A3 ;;stk-pi/2 x, y, r, pi/2.
DEFB $38 ;;end-calc x, y, r, pi/2.
; Change the exponent of pi/2 from $81 to $83 giving 2*PI the central angle.
; This is quicker than multiplying by four.
LD (HL),$83 ; x, y, r, 2*PI.
; Now store this important constant in mem-5 and delete so that other
; parameters can be derived from it, by a routine shared with DRAW.
RST 28H ;; FP-CALC x, y, r, 2*PI.
DEFB $C5 ;;st-mem-5 store 2*PI in mem-5
DEFB $02 ;;delete x, y, r.
DEFB $38 ;;end-calc x, y, r.
; The parameters derived from mem-5 (A) and from the radius are set up in
; four of the other mem locations by the CIRCLE DRAW PARAMETERS routine which
; also returns the number of straight lines in the B register.
CALL L247D ; routine CD-PRMS1
; mem-0 ; A/No of lines (=a) unused
; mem-1 ; sin(a/2) will be moving x var
; mem-2 ; - will be moving y var
; mem-3 ; cos(a) const
; mem-4 ; sin(a) const
; mem-5 ; Angle of rotation (A) (2*PI) const
; B ; Number of straight lines.
PUSH BC ; Preserve the number of lines in B.
; Next calculate the length of half a chord by multiplying the sine of half
; the central angle by the radius of the circle.
RST 28H ;; FP-CALC x, y, r.
DEFB $31 ;;duplicate x, y, r, r.
DEFB $E1 ;;get-mem-1 x, y, r, r, sin(a/2).
DEFB $04 ;;multiply x, y, r, half-chord.
DEFB $38 ;;end-calc x, y, r, half-chord.
LD A,(HL) ; fetch exponent of the half arc to A.
CP $80 ; compare to a half pixel
JR NC,L235A ; forward, if greater than .5, to C-ARC-GE1
; If the first line is less than .5 then 4 'lines' would be drawn on the same
; spot so tidy the calculator stack and machine stack and plot the centre.
RST 28H ;; FP-CALC x, y, r, hc.
DEFB $02 ;;delete x, y, r.
DEFB $02 ;;delete x, y.
DEFB $38 ;;end-calc x, y.
POP BC ; Balance machine stack by taking chord-count.
JP L22DC ; JUMP to PLOT
; ---
; The arc is greater than 0.5 so the circle can be drawn.
;; C-ARC-GE1
L235A: RST 28H ;; FP-CALC x, y, r, hc.
DEFB $C2 ;;st-mem-2 x, y, r, half chord to mem-2.
DEFB $01 ;;exchange x, y, hc, r.
DEFB $C0 ;;st-mem-0 x, y, hc, r.
DEFB $02 ;;delete x, y, hc.
; Subtract the length of the half-chord from the absolute y coordinate to
; give the starting y coordinate sy.
; Note that for a circle this is also the end coordinate.
DEFB $03 ;;subtract x, y-hc. (The start y-coord)
DEFB $01 ;;exchange sy, x.
; Next simply add the radius to the x coordinate to give a fuzzy x-coordinate.
; Strictly speaking, the radius should be multiplied by cos(a/2) first but
; doing it this way makes the circle slightly larger.
DEFB $E0 ;;get-mem-0 sy, x, r.
DEFB $0F ;;addition sy, x+r. (The start x-coord)
; We now want three copies of this pair of values on the calculator stack.
; The first pair remain on the stack throughout the circle routine and are
; the end points. The next pair will be the moving absolute values of x and y
; that are updated after each line is drawn. The final pair will be loaded
; into the COORDS system variable so that the first vertical line starts at
; the right place.
DEFB $C0 ;;st-mem-0 sy, sx.
DEFB $01 ;;exchange sx, sy.
DEFB $31 ;;duplicate sx, sy, sy.
DEFB $E0 ;;get-mem-0 sx, sy, sy, sx.
DEFB $01 ;;exchange sx, sy, sx, sy.
DEFB $31 ;;duplicate sx, sy, sx, sy, sy.
DEFB $E0 ;;get-mem-0 sx, sy, sx, sy, sy, sx.
; Locations mem-1 and mem-2 are the relative x and y values which are updated
; after each line is drawn. Since we are drawing a vertical line then the rx
; value in mem-1 is zero and the ry value in mem-2 is the full chord.
DEFB $A0 ;;stk-zero sx, sy, sx, sy, sy, sx, 0.
DEFB $C1 ;;st-mem-1 sx, sy, sx, sy, sy, sx, 0.
DEFB $02 ;;delete sx, sy, sx, sy, sy, sx.
; Although the three pairs of x/y values are the same for a circle, they
; will be labelled terminating, absolute and start coordinates.
DEFB $38 ;;end-calc tx, ty, ax, ay, sy, sx.
; Use the exponent manipulating trick again to double the value of mem-2.
INC (IY+$62) ; Increment MEM-2-1st doubling half chord.
; Note. this first vertical chord is drawn at the radius so circles are
; slightly displaced to the right.
; It is only necessary to place the values (sx) and (sy) in the system
; variable COORDS to ensure that drawing commences at the correct pixel.
; Note. a couple of LD (COORDS),A instructions would have been quicker, and
; simpler, than using LD (COORDS),HL.
CALL L1E94 ; routine FIND-INT1 fetches sx from stack to A.
LD L,A ; place X value in L.
PUSH HL ; save the holding register.
CALL L1E94 ; routine FIND-INT1 fetches sy to A
POP HL ; restore the holding register.
LD H,A ; and place y value in high byte.
LD ($5C7D),HL ; Update the COORDS system variable.
;
; tx, ty, ax, ay.
POP BC ; restore the chord count
; values 4,8,12,16,20,24,28 or 32.
JP L2420 ; forward to DRW-STEPS
; tx, ty, ax, ay.
; Note. the jump to DRW-STEPS is just to decrement B and jump into the
; middle of the arc-drawing loop. The arc count which includes the first
; vertical arc draws one less than the perceived number of arcs.
; The final arc offsets are obtained by subtracting the final COORDS value
; from the initial sx and sy values which are kept at the base of the
; calculator stack throughout the arc loop.
; This ensures that the final line finishes exactly at the starting pixel
; removing the possibility of any inaccuracy.
; Since the initial sx and sy values are not required until the final arc
; is drawn, they are not shown until then.
; As the calculator stack is quite busy, only the active parts are shown in
; each section.
; ------------------
; THE 'DRAW' COMMAND
; ------------------
; The Spectrum's DRAW command is overloaded and can take two parameters sets.
;
; With two parameters, it simply draws an approximation to a straight line
; at offset x,y using the LINE-DRAW routine.
;
; With three parameters, an arc is drawn to the point at offset x,y turning
; through an angle, in radians, supplied by the third parameter.
; The arc will consist of 4 to 252 straight lines each one of which is drawn
; by calls to the DRAW-LINE routine.
;; DRAW
L2382: RST 18H ; GET-CHAR
CP $2C ; is it the comma character ?
JR Z,L238D ; forward, if so, to DR-3-PRMS
; There are two parameters e.g. DRAW 255,175
CALL L1BEE ; routine CHECK-END
JP L2477 ; jump forward to LINE-DRAW
; ---
; There are three parameters e.g. DRAW 255, 175, .5
; The first two are relative coordinates and the third is the angle of
; rotation in radians (A).
;; DR-3-PRMS
L238D: RST 20H ; NEXT-CHAR skips over the 'comma'.
CALL L1C82 ; routine EXPT-1NUM stacks the rotation angle.
CALL L1BEE ; routine CHECK-END
; Now enter the calculator and store the complete rotation angle in mem-5
RST 28H ;; FP-CALC x, y, A.
DEFB $C5 ;;st-mem-5 x, y, A.
; Test the angle for the special case of 360 degrees.
DEFB $A2 ;;stk-half x, y, A, 1/2.
DEFB $04 ;;multiply x, y, A/2.
DEFB $1F ;;sin x, y, sin(A/2).
DEFB $31 ;;duplicate x, y, sin(A/2),sin(A/2)
DEFB $30 ;;not x, y, sin(A/2), (0/1).
DEFB $30 ;;not x, y, sin(A/2), (1/0).
DEFB $00 ;;jump-true x, y, sin(A/2).
DEFB $06 ;;forward to L23A3, DR-SIN-NZ
; if sin(r/2) is not zero.
; The third parameter is 2*PI (or a multiple of 2*PI) so a 360 degrees turn
; would just be a straight line. Eliminating this case here prevents
; division by zero at later stage.
DEFB $02 ;;delete x, y.
DEFB $38 ;;end-calc x, y.
JP L2477 ; forward to LINE-DRAW
; ---
; An arc can be drawn.
;; DR-SIN-NZ
L23A3: DEFB $C0 ;;st-mem-0 x, y, sin(A/2). store mem-0
DEFB $02 ;;delete x, y.
; The next step calculates (roughly) the diameter of the circle of which the
; arc will form part. This value does not have to be too accurate as it is
; only used to evaluate the number of straight lines and then discarded.
; After all for a circle, the radius is used. Consequently, a circle of
; radius 50 will have 24 straight lines but an arc of radius 50 will have 20
; straight lines - when drawn in any direction.
; So that simple arithmetic can be used, the length of the chord can be
; calculated as X+Y rather than by Pythagoras Theorem and the sine of the
; nearest angle within reach is used.
DEFB $C1 ;;st-mem-1 x, y. store mem-1
DEFB $02 ;;delete x.
DEFB $31 ;;duplicate x, x.
DEFB $2A ;;abs x, x (+ve).
DEFB $E1 ;;get-mem-1 x, X, y.
DEFB $01 ;;exchange x, y, X.
DEFB $E1 ;;get-mem-1 x, y, X, y.
DEFB $2A ;;abs x, y, X, Y (+ve).
DEFB $0F ;;addition x, y, X+Y.
DEFB $E0 ;;get-mem-0 x, y, X+Y, sin(A/2).
DEFB $05 ;;division x, y, X+Y/sin(A/2).
DEFB $2A ;;abs x, y, X+Y/sin(A/2) = D.
; Bring back sin(A/2) from mem-0 which will shortly get trashed.
; Then bring D to the top of the stack again.
DEFB $E0 ;;get-mem-0 x, y, D, sin(A/2).
DEFB $01 ;;exchange x, y, sin(A/2), D.
; Note. that since the value at the top of the stack has arisen as a result
; of division then it can no longer be in integer form and the next re-stack
; is unnecessary. Only the Sinclair ZX80 had integer division.
DEFB $3D ;;re-stack (unnecessary)
DEFB $38 ;;end-calc x, y, sin(A/2), D.
; The next test avoids drawing 4 straight lines when the start and end pixels
; are adjacent (or the same) but is probably best dispensed with.
LD A,(HL) ; fetch exponent byte of D.
CP $81 ; compare to 1
JR NC,L23C1 ; forward, if > 1, to DR-PRMS
; else delete the top two stack values and draw a simple straight line.
RST 28H ;; FP-CALC
DEFB $02 ;;delete
DEFB $02 ;;delete
DEFB $38 ;;end-calc x, y.
JP L2477 ; to LINE-DRAW
; ---
; The ARC will consist of multiple straight lines so call the CIRCLE-DRAW
; PARAMETERS ROUTINE to pre-calculate sine values from the angle (in mem-5)
; and determine also the number of straight lines from that value and the
; 'diameter' which is at the top of the calculator stack.
;; DR-PRMS
L23C1: CALL L247D ; routine CD-PRMS1
; mem-0 ; (A)/No. of lines (=a) (step angle)
; mem-1 ; sin(a/2)
; mem-2 ; -
; mem-3 ; cos(a) const
; mem-4 ; sin(a) const
; mem-5 ; Angle of rotation (A) in
; B ; Count of straight lines - max 252.
PUSH BC ; Save the line count on the machine stack.
; Remove the now redundant diameter value D.
RST 28H ;; FP-CALC x, y, sin(A/2), D.
DEFB $02 ;;delete x, y, sin(A/2).
; Dividing the sine of the step angle by the sine of the total angle gives
; the length of the initial chord on a unary circle. This factor f is used
; to scale the coordinates of the first line which still points in the
; direction of the end point and may be larger.
DEFB $E1 ;;get-mem-1 x, y, sin(A/2), sin(a/2)
DEFB $01 ;;exchange x, y, sin(a/2), sin(A/2)
DEFB $05 ;;division x, y, sin(a/2)/sin(A/2)
DEFB $C1 ;;st-mem-1 x, y. f.
DEFB $02 ;;delete x, y.
; With the factor stored, scale the x coordinate first.
DEFB $01 ;;exchange y, x.
DEFB $31 ;;duplicate y, x, x.
DEFB $E1 ;;get-mem-1 y, x, x, f.
DEFB $04 ;;multiply y, x, x*f (=xx)
DEFB $C2 ;;st-mem-2 y, x, xx.
DEFB $02 ;;delete y. x.
; Now scale the y coordinate.
DEFB $01 ;;exchange x, y.
DEFB $31 ;;duplicate x, y, y.
DEFB $E1 ;;get-mem-1 x, y, y, f
DEFB $04 ;;multiply x, y, y*f (=yy)
; Note. 'sin' and 'cos' trash locations mem-0 to mem-2 so fetch mem-2 to the
; calculator stack for safe keeping.
DEFB $E2 ;;get-mem-2 x, y, yy, xx.
; Once we get the coordinates of the first straight line then the 'ROTATION
; FORMULA' used in the arc loop will take care of all other points, but we
; now use a variation of that formula to rotate the first arc through (A-a)/2
; radians.
;
; xRotated = y * sin(angle) + x * cos(angle)
; yRotated = y * cos(angle) - x * sin(angle)
;
DEFB $E5 ;;get-mem-5 x, y, yy, xx, A.
DEFB $E0 ;;get-mem-0 x, y, yy, xx, A, a.
DEFB $03 ;;subtract x, y, yy, xx, A-a.
DEFB $A2 ;;stk-half x, y, yy, xx, A-a, 1/2.
DEFB $04 ;;multiply x, y, yy, xx, (A-a)/2. (=angle)
DEFB $31 ;;duplicate x, y, yy, xx, angle, angle.
DEFB $1F ;;sin x, y, yy, xx, angle, sin(angle)
DEFB $C5 ;;st-mem-5 x, y, yy, xx, angle, sin(angle)
DEFB $02 ;;delete x, y, yy, xx, angle
DEFB $20 ;;cos x, y, yy, xx, cos(angle).
; Note. mem-0, mem-1 and mem-2 can be used again now...
DEFB $C0 ;;st-mem-0 x, y, yy, xx, cos(angle).
DEFB $02 ;;delete x, y, yy, xx.
DEFB $C2 ;;st-mem-2 x, y, yy, xx.
DEFB $02 ;;delete x, y, yy.
DEFB $C1 ;;st-mem-1 x, y, yy.
DEFB $E5 ;;get-mem-5 x, y, yy, sin(angle)
DEFB $04 ;;multiply x, y, yy*sin(angle).
DEFB $E0 ;;get-mem-0 x, y, yy*sin(angle), cos(angle)
DEFB $E2 ;;get-mem-2 x, y, yy*sin(angle), cos(angle), xx.
DEFB $04 ;;multiply x, y, yy*sin(angle), xx*cos(angle).
DEFB $0F ;;addition x, y, xRotated.
DEFB $E1 ;;get-mem-1 x, y, xRotated, yy.
DEFB $01 ;;exchange x, y, yy, xRotated.
DEFB $C1 ;;st-mem-1 x, y, yy, xRotated.
DEFB $02 ;;delete x, y, yy.
DEFB $E0 ;;get-mem-0 x, y, yy, cos(angle).
DEFB $04 ;;multiply x, y, yy*cos(angle).
DEFB $E2 ;;get-mem-2 x, y, yy*cos(angle), xx.
DEFB $E5 ;;get-mem-5 x, y, yy*cos(angle), xx, sin(angle).
DEFB $04 ;;multiply x, y, yy*cos(angle), xx*sin(angle).
DEFB $03 ;;subtract x, y, yRotated.
DEFB $C2 ;;st-mem-2 x, y, yRotated.
; Now the initial x and y coordinates are made positive and summed to see
; if they measure up to anything significant.
DEFB $2A ;;abs x,