#define DEFB .BYTE
#define DEFW .WORD
#define EQU .EQU
#define ORG .ORG
; ========================
; UTILITY3 v1.3
; ========================
;
; UTILITY3 a disassembler for the ZX Spectrum which
; incorporates routine DIS-Z80 by John Kerr.
; It also uses adaptations of scrolling routines
; and keyboard-reading routines from the Spectrum ROM.
; The pocket calculator style font looks a little familiar too.
;
; ========================
; ========================
;
; U3 is a self-contained, screen-resident disassembler written in
; 2K of memory. It is designed to load at address $4000 and re-locate
; itself to $5000. The main subroutine, DIS-Z80 was written by John Kerr
; and published in SUBSET 1987.
; The program will work on any Spectrum and doesn't make OS calls.
;
;========================
ORG $5000
; Note this section is
; normally executed at $4000
LD HL,$4000 ; begin by relocating the entire 2K
LD DE,$5000 ; block of instructions from the top
LD BC,$0800 ; third of the screen to the lower
LDIR ; third creating a print area in the
; top two thirds - 16 lines numbered
; line 0 - line 15.
; Ensure that the attributes at end of line 15 are black ink on cyan paper.
LD HL,$59FC
ATTLP LD (HL),$28
INC L
JR NZ,ATTLP
DEC L
; copy the colour attributes on line 15 to preceding lines 0-14.
; Note a cyan column helps highlight the ASCII text.
LD DE,$59DF ; end of line 14 attributes.
LD BC,$01E0 ; number of bytes to fill.
LDDR
; Now check if Interface 1 is present and initialized
; If so allow ROM 4 to be paged. (Not relevant to +3).
; This cautious approach prevents a BASIC error code being generated
; should Interface 1 not be present.
LD A,(23734) ; shadow system variable FLAGS3
; or first byte of CHANS area.
AND A ; test - will be zero if shadow ROM initialized.
JR NZ,NOSHDW ; skip to NOSHDW if not
LD HL,MAXROM ; enable paging of Shadow ROM
INC (HL) ; increase from 4 to 5.
NOSHDW JP MAIN ; jump to main entry point now in lower screen
; --------------------------------------------------------------------
; The above code although copied to lower screen is no longer required
; If space were at a premium it could be executed on another screen line.
; --------------------------------------------------------------------
; --------------
; The next routine pages in a ROM in the range 0-4
; --------------
ROM DI ; disable interrupts until end.
LD A,'?' ; prompt
LD ($50FF),A ; "ROM?"
CALL ROMTXT ; large
ROML CALL KEY ; wait for a valid keypress.
LD HL,MAXROM ; holds 4 or 5
CP (HL) ; compare against upper limit 4/5
JR NC,ROML ; loop back if too high.
LD E,A ; select ROM
CALL ROMSEL ; and continue into disassembly loop.
; Note. the call to ROMSEL puts the address of MAIN on the stack.
;========================
;
; Initial Entry Point.
;
;========================
MAIN LD HL,0 ; start address is initially zero
; and reset to zero after a ROM switch.
MAINLP LD (DISADD),HL ; update disassembly address.
CALL ROMTXT ; large print in lower screen shows
; the current ROM.
; The start of the main disassembly loop.
DLOOP LD B,8 ; disassemble 8 lines at a time.
BLOOP PUSH BC ; save line count.
CALL SCROLL ; scroll top 16 lines upwards
LD DE,(DISADD) ; pick up address in DE
PUSH DE ; save it
;------------------------
CALL DISZ80 ; disassemble one instruction.
;------------------------
LD (DISADD),DE ; save new disassembly address.
LD B,3 ; print
GAP CALL CHROP ; a three
DJNZ GAP ; space gap.
POP HL ; pop the old disassembly address
TEXTLP LD A,(HL) ; print
INC HL ; ASCII
CALL CHROP ; TEXT to help distinguish
AND A ; instructions
SBC HL,DE ; from data.
JR NC,TXTEND ; finished when addresses match.
ADD HL,DE ; loop back until HL matches DE
JR TEXTLP ; could be 1 to 4 characters
TXTEND POP BC ; restore the counter
DJNZ BLOOP ; and loop back for 8 lines
CALL KEY ; get a keypress.
CP 16 ; is it Enter ?
JR Z,DLOOP ; back if so for another 8 lines.
CP 17 ; is it 'R' ?
JR Z,ROM ; back to ROM routine if so.
CP 18 ; is it 'Q' ?
JR Z,QUIT ; forward if so to quit
; By elimination a numeric key (0-F) has been pressed so continue to build
; up a hex number. The HL pair will initially hold 0 from the KEY routine.
; First time through the loop, the value will be $00 - $0F. Any key higher,
; usually ENTER, causes the hex input to be accepted.
HEX_LP CP $10 ; is key higher than hex digit ?
JR NC,MAINLP ; back to main loop with ENTER, etc.
; and a new disassembly address.
ADD HL,HL ; rotate the
ADD HL,HL ; nibble to the left
ADD HL,HL ; losing the
ADD HL,HL ; 5'th character.
OR L
LD L,A ; insert new hex digit.
EX DE,HL ; transfer address to DE
CALL CLINE ; clear line 15
CALL ADRSP ; print DE as HEX then a space
PUSH DE ; save the address.
CALL BIGPR ; scan text to produce large text
; in lower third.
POP HL ; restore address to HL.
LD D,$A0 ; outer adjustable delay counter.
DELAY PUSH HL ; 21-cycle
POP HL ; delay.
PUSH HL ; and again.
POP HL ;
DJNZ DELAY ; decrement inner counter and loop
DEC D ; decrement outer counter.
JR NZ,DELAY ; back to DELAY1 while D not zero.
CALL KEY ; get a keypress.
JR HEX_LP ; and back to hex input loop
; ------------------
;
; Select ROM.
;
; ------------------
ROM3 LD E,3 ; Amstrad named the original ROM ROM3.
ROMSEL LD A,($700) ; fetch the byte at location $700.
CP 201 ; is it the RET instruction ?
CALL Z,$700 ; if it is then call it.
; Note. Interface 1 is un-paged by an instruction fetch on 0x700. The above
; code would have no ill effects if another ROM had a RET at same address.
LD A,E ; fetch desired ROM $00-$04
OR '0' ; add to ascii base character.
LD ($50FF),A ; place after letters "ROM"
CP '4' ; is Interface 1 ROM required.
JR NZ,PLUS3 ; forward to consider 128K ROMS
DEC E ; change 4 to 3.
CALL PLUS3 ; ensure main Basic ROM is active.
LD HL,0 ; a dummy address
PUSH HL ; is pushed on the stack.
JP $0008 ; jump to location $0008.
; Note. An instruction fetch on address 8 pages in Interface 1.
; A routine in the Interface 1 ROM will drop the zero off the stack.
; It will then return to the Main Entry Point leaving the shadow ROM paged in.
; This method which tricks Interface 1 into thinking that the CALBAS routine
; has been used, avoids writing to RAM areas outside the screen area.
; Use this program with an Interface 1 supporting emulator to see what happens
; on the other side. Or use with the real hardware.
; The varous 128K Spectrums page in the various ROMS using OUT instructions.
; These have no effect on Spectrums that have only a single ROM.
PLUS3 LD A,(23399)
AND 248
BIT 1,E
JR Z,SW1
OR 4
SW1 LD BC,$1FFD
OUT (C),A
LD A,(23388)
BIT 0,E
JR NZ,SW2
RES 4,A
SW2 LD BC,$7FFD
OUT (C),A
RET
;====================
;
; Before returning to BASIC select the main ROM, discourage re-entry
; with an all-white display and enable interrupts.
;
;====================
QUIT CALL ROM3
LD HL,$57FF
LD DE,$5800
LD BC,$0300
LDIR
EI
LABEND RET ; Finish >>>
; ---
; Note. there is a gap of approx 16 unused bytes here.
; ---
ORG $50F8
; Three Program Variables.
DISADD DEFW 0 ; two byte disassembly address.
PRIPOS DEFB 0 ; low byte of print position.
MAXROM DEFB 4 ; one more than maximum ROM allowed.
; ---
ORG $50FC
; This message terminates at a page boundary and requires no end marker.
DEFB "ROM3"
; ====================
; DIS-Z80 was published in the SUBSET column of Personal Computer World 1987.
; The routine disassembles a single Z80 instruction at address DE.
; It is required to be followed by a routine called CHROP that outputs a
; single ASCII character.
; It was originally developed for CP/M on an Amstrad CPC128.
; The original ORG was $0100. I have added $5000 to all addresses.
; The stated aim was to write a Z80 disassembly routine in as short a space
; as possible and, at just over 1K (1090 bytes), it is a rather incredible
; program.
; The SUBSET editor David Barrow was able to trim only one byte from John
; Kerr's compact code. I've forgotten where so there's a challenge.
; ====================
ORG $5100
DISZ80 CALL ADRSP
LD BC,$0900
LD HL,$2020
BUFFER PUSH HL
DJNZ BUFFER
LD H,B
LD L,C
ADD HL,SP
PUSH BC
EX (SP),IX
PUSH BC
PUSH BC
ADD IX,SP
PUSH HL
LD HL,GROUP3
TRYNDX CALL FETCH
LD B,C
CP $ED
JR Z,CONFLG
INC B
CP $DD
JR Z,CONFLG
INC B
CP $FD
JR NZ,NOTNDX
CONFLG LD (IX+1),B
INC B
DJNZ TRYNDX
JR NXBYTE
NOTNDX LD C,A
LD A,(IX+1)
OR A
JR Z,NODISP
LD A,C
CP $CB
JR Z,GETDIS
AND $44
CP 4
JR Z,GETDIS
LD A,C
AND $C0
CP $40
JR NZ,NODISP
GETDIS CALL FETCH
LD (IX+2),A
NODISP LD HL,GROUP1
LD A,C
CP $CB
JR NZ,NEWMSK
LD HL,GROUP2
NXBYTE CALL FETCH
LD C,A
NEWMSK LD A,(HL)
OR A
JR Z,TABEND
AND C
INC HL
NEWMOD LD B,(HL)
INC HL
INC B
JR Z,NEWMSK
TRYMAT CP (HL)
INC HL
JR Z,GETNDX
BIT 7,(HL)
INC HL
JR Z,TRYMAT
JR NEWMOD
GETNDX LD A,(HL)
AND $7F
DEC B
TABEND POP HL
PUSH DE
PUSH HL
EX DE,HL
LD HL,MONICS
CALL XTRACT
POP HL
LD DE,5
ADD HL,DE
POP DE
LD A,B
AND $F0
JR Z,SECOND
RRA
RRA
RRA
RRA
PUSH BC
LD B,A
LD A,C
CALL OPRND1
POP BC
LD A,B
AND $0F
JR Z,OPDONE
LD (HL),44 ;,
INC HL
SECOND LD A,B
AND $0F
LD B,A
LD A,C
CALL NZ,OPRND2
OPDONE LD A,3
SUB (IX)
POP HL
POP HL
POP IX
JR C,OUTEXT
INC A
LD B,A
ADD A,B
ADD A,B
LD B,A
SPACES LD A,$20
CALL CHROP
DJNZ SPACES
OUTEXT LD B,18
PUTOUT DEC SP
POP HL
LD A,H
CALL CHROP
DJNZ PUTOUT
RET
;***********************
GROUP2 DEFB $C0,$36,$40
DEFB $04,$80,$2D,$C0,$BE
DEFB $FF,$F8,$06,$00,$33
DEFB $08,$38,$10,$35,$18
DEFB $3A,$20,$3F,$28,$40
DEFB $30,$00,$38,$C1
GROUP1 DEFB $FF,$00,$00
DEFB $24,$07,$32,$0F,$37
DEFB $17,$31,$1F,$36,$27
DEFB $0D,$2F,$0B,$37,$3D
DEFB $3F,$06,$76,$14,$C9
DEFB $30,$D9,$12,$F3,$0F
DEFB $FB,$91,$72,$C6,$02
DEFB $CE,$01,$DE,$BC,$02
DEFB $D6,$42,$E6,$03,$EE
DEFB $43,$F6,$25,$FE,$8C
DEFB $04,$08,$93,$01,$10
DEFB $10,$18,$9D,$AF,$22
DEFB $A2,$FA,$2A,$A2,$A7
DEFB $32,$A2,$7A,$3A,$A2
DEFB $03,$C3,$1C,$CD,$85
DEFB $97,$D3,$AA,$79,$DB
DEFB $9B,$5F,$E3,$93,$0E
DEFB $E9,$9C,$05,$EB,$93
DEFB $DF,$F9,$A2,$FF,$C0
DEFB $B6,$40,$A2,$FF,$F8
DEFB $76,$80,$02,$88,$01
DEFB $98,$BC,$06,$90,$42
DEFB $A0,$03,$A8,$43,$B0
DEFB $25,$B8,$8C,$FF,$C7
DEFB $0B,$04,$16,$05,$8E
DEFB $B2,$06,$A2,$20,$C0
DEFB $B0,$23,$C2,$1C,$C4
DEFB $85,$10,$C7,$BB,$FF
DEFB $CF,$D3,$01,$A2,$0D
DEFB $03,$16,$0B,$8E,$FD
DEFB $09,$82,$60,$C1,$2B
DEFB $C5,$AC,$FF,$E7,$21
DEFB $20,$9D,$FF,$EF,$E7
DEFB $02,$A2,$7E,$0A,$A2
GROUP3 DEFB $FF,$00,$44
DEFB $23,$45,$2F,$4D,$2E
DEFB $4E,$00,$67,$39,$6F
DEFB $34,$70,$00,$71,$00
DEFB $A0,$21,$A1,$0A,$A2
DEFB $1A,$A3,$29,$A8,$1F
DEFB $A9,$08,$AA,$18,$AB
DEFB $28,$B0,$20,$B1,$09
DEFB $B2,$19,$B3,$27,$B8
DEFB $1E,$B9,$07,$BA,$17
DEFB $BB,$A6,$FF,$C7,$B8
DEFB $40,$9B,$8B,$41,$AA
DEFB $FF,$CF,$FD,$42,$3C
DEFB $4A,$81,$AD,$43,$A2
DEFB $DA,$4B,$A2,$FF,$E7
DEFB $40,$46,$95,$FF,$F7
DEFB $C7,$47,$A2,$7C,$57
DEFB $A2,$FF,$00
;_______________
MONICS DEFB $BF
DEFB 'A','D','C'+$80 ; ADC
DEFB 'A','D','D'+$80 ; ADD
DEFB 'A','N','D'+$80 ; AND
DEFB 'B','I','T'+$80 ; BIT
DEFB 'C','A','L','L'+$80 ; CALL
DEFB 'C','C','F'+$80 ; CCF
DEFB 'C','P','D','R'+$80 ; CPDR
DEFB 'C','P','D'+$80 ; CPD
DEFB 'C','P','I','R'+$80 ; CPIR
DEFB 'C','P','I'+$80 ; CPI
DEFB 'C','P','L'+$80 ; CPL
DEFB 'C','P'+$80 ; CP
DEFB 'D','A','A'+$80 ; DAA
DEFB 'D','E','C'+$80 ; DEC
DEFB 'D','I'+$80 ; DI
DEFB 'D','J','N','Z'+$80 ; DJNZ
DEFB 'E','I'+$80 ; EI
DEFB 'E','X','X'+$80 ; EXX
DEFB 'E','X'+$80 ; EX
DEFB 'H','A','L','T'+$80 ; HALT
DEFB 'I','M'+$80 ; IM
DEFB 'I','N','C'+$80 ; INC
DEFB 'I','N','D','R'+$80 ; INDR
DEFB 'I','N','D'+$80 ; IND
DEFB 'I','N','I','R'+$80 ; INIR
DEFB 'I','N','I'+$80 ; INI
DEFB 'I','N'+$80 ; IN
DEFB 'J','P'+$80 ; JP
DEFB 'J','R'+$80 ; JR
DEFB 'L','D','D','R'+$80 ; LDDR
DEFB 'L','D','D'+$80 ; LDD
DEFB 'L','D','I','R'+$80 ; LDIR
DEFB 'L','D','I'+$80 ; LDI
DEFB 'L','D'+$80 ; LD
DEFB 'N','E','G'+$80 ; NEG
DEFB 'N','O','P'+$80 ; NOP
DEFB 'O','R'+$80 ; OR
DEFB 'O','T','D','R'+$80 ; OTDR
DEFB 'O','T','I','R'+$80 ; OTIR
DEFB 'O','U','T','D'+$80 ; OUTD
DEFB 'O','U','T','I'+$80 ; OUTI
DEFB 'O','U','T'+$80 ; OUT
DEFB 'P','O','P'+$80 ; POP
DEFB 'P','U','S','H'+$80 ; PUSH
DEFB 'R','E','S'+$80 ; RES
DEFB 'R','E','T','I'+$80 ; RETI
DEFB 'R','E','T','N'+$80 ; RETN
DEFB 'R','E','T'+$80 ; RET
DEFB 'R','L','A'+$80 ; RLA
DEFB 'R','L','C','A'+$80 ; RLCA
DEFB 'R','L','C'+$80 ; RLC
DEFB 'R','L','D'+$80 ; RLD
DEFB 'R','L'+$80 ; RL
DEFB 'R','R','A'+$80 ; RRA
DEFB 'R','R','C','A'+$80 ; RA
DEFB 'R','R','C'+$80 ; RRC
DEFB 'R','R','D'+$80 ; RRD
DEFB 'R','R'+$80 ; RR
DEFB 'R','S','T'+$80 ; RST
DEFB 'S','B','C'+$80 ; SBC
DEFB 'S','C','F'+$80 ; SCF
DEFB 'S','E','T'+$80 ; SET
DEFB 'S','L','A'+$80 ; SLA
DEFB 'S','R','A'+$80 ; SRA
DEFB 'S','R','L'+$80 ; SRL
DEFB 'S','U','B'+$80 ; SUB
DEFB 'X','O','R'+$80 ; XOR
;*****************
OPRND1 DJNZ CONDIT
RSTADR AND $38
JR DA
OPRND2 DJNZ DAT8
RELADR CALL FETCH
LD C,A
RLA
SBC A,A
LD B,A
EX DE,HL
PUSH HL
ADD HL,BC
JR DHL
CONDIT RRA
RRA
RRA
DJNZ BITNUM
BIT 4,A
JR NZ,ABS
AND 3
ABS AND 7
ADD A,$14
JR PS1
DAT8 DJNZ DAT16
D8 CALL FETCH
JR DA
BITNUM DJNZ INTMOD
AND 7
DA LD C,A
SUB A
JR DAC
DAT16 DJNZ EXAF
D16 CALL FETCH
LD C,A
CALL FETCH
DAC EX DE,HL
PUSH HL
LD H,A
LD L,C
DHL LD C,$F8
PUSH HL
CALL CONVHL
POP HL
LD BC,$000A
OR A
SBC HL,BC
POP HL
EX DE,HL
RET C
LD (HL),'H'
INC HL
RET
INTMOD DJNZ STKTOP
AND 3
ADD A,$1C
PS1 JR PS3
STKTOP LD C,$13
DEC B
JR Z,PS2
REG16P DJNZ COMMON
RRA
AND 3
CP 3
JR NZ,RX
DEC A
JR RNX
EXAF LD C,$0A
DEC B
JR Z,PS2
EXDE INC C
DEC B
JR Z,PS2
REG8S DJNZ ACCUM
R8 AND 7
CP 6
JR NZ,PS3
LD (HL),'('
INC HL
CALL REGX
LD A,(IX+2)
OR A
JR Z,RP
LD (HL),43 ;+
RLCA
RRCA
JR NC,POS
LD (HL),45 ;-
NEG
POS INC HL
EX DE,HL
PUSH HL
LD H,B
LD L,A
LD C,$FB
CALL CONVHL
POP HL
EX DE,HL
JR RP
ACCUM RRA
RRA
RRA
COMMON LD C,7
DEC B
JR Z,PS2
PORTC DEC C
DJNZ IDAT8
PS2 LD A,C
PS3 JR PS4
IDAT8 DJNZ IDAT16
LD (HL),'('
INC HL
CALL D8
JR RP
IDAT16 DJNZ REG8
LD (HL),'('
INC HL
CALL D16
JR RP
REG8 DEC B
JR Z,R8
IPAREF DJNZ REG16
AND 9
JR PS4
REG16 RRA
DJNZ IREG16
R16 AND 3
RX CP 2
JR Z,REGX
RNX ADD A,$0C
JR PS4
IREG16 DJNZ REGX
LD (HL),'('
INC HL
CALL R16
RP LD (HL),')'
INC HL
RET
REGX LD A,(IX+1)
ADD A,$10
PS4 EX DE,HL
PUSH HL
LD HL,RGSTRS
CALL XTRACT
POP HL
EX DE,HL
RET
;*************
RGSTRS DEFB 'B' +$80
DEFB 'C' +$80
DEFB 'D' +$80
DEFB 'E' +$80
DEFB 'H' +$80
DEFB 'L' +$80
DEFB "(","C",')' +$80
DEFB 'A' +$80
DEFB 'I' +$80
DEFB 'R' +$80
DEFB "A","F",",","A","F",''' +$80
DEFB "D","E",",","H",'L' +$80
DEFB "B",'C' +$80
DEFB "D",'E' +$80
DEFB "A",'F' +$80
DEFB "S",'P' +$80
DEFB "H",'L' +$80
DEFB "I",'X' +$80
DEFB "I",'Y' +$80
DEFB "(","S","P",')' +$80
DEFB "N",'Z' +$80
DEFB 'Z' +$80
DEFB "N",'C' +$80
DEFB 'C' +$80
DEFB "P",'O' +$80
DEFB "P",'E' +$80
DEFB 'P' +$80
DEFB 'M' +$80
DEFB '0' +$80
DEFB '?' +$80
DEFB '1' +$80
DEFB '2' +$80
;********************
CONVHL SUB A
CVHL1 PUSH AF
SUB A
LD B,16
CVHL2 ADD A,C
JR C,CVHL3
SUB C
CVHL3 ADC HL,HL
RLA
DJNZ CVHL2
JR NZ,CVHL1
CP 10
INC B
JR NC,CVHL1
CVHL4 CP 10
SBC A,$69
DAA
LD (DE),A
INC DE
POP AF
JR NZ,CVHL4
RET
;****************
XTRACT OR A
JR Z,COPY
SKIP BIT 7,(HL)
INC HL
JR Z,SKIP
DEC A
JR NZ,SKIP
COPY LD A,(HL)
RLCA
SRL A
LD (DE),A
INC DE
INC HL
JR NC,COPY
RET
;*******************
FETCH LD A,(DE)
INC DE
INC (IX+0)
PUSH AF
CALL BYTSP
POP AF
RET
ADRSP LD A,D
CALL BYTOP
LD A,E
BYTSP CALL BYTOP
LD A,$20
JR CHROP
BYTOP PUSH AF
RRA
RRA
RRA
RRA
CALL HEXOP
POP AF
HEXOP AND $0F
CP 10
SBC A,$69
DAA
; -----------------------------------
;
; End of John Kerr's DIS-Z80 routine.
;
; The next routine outputs a character.
;
; -------------------------------------
CHROP PUSH HL
PUSH DE
PUSH BC
CALL RITE
POP BC
POP DE
POP HL
RET
;=======================
;
; This scrolling subroutine scrolls the lower 15 lines up by one character
; position. Text line 8 is copied across a third of the screen to text
; line 7. Text line 8 is also, for simplicity, copied to line 15 just before
; line 15 is cleared. This is purely to enable the DE register to advance
; linearly while the source register is adjusted to pick up the appropriate
; text.
;
;=======================
SCROLL LD HL,$4020 ; set source
LD DE,$4000 ; set destination
SLOOP LD BC,$00E0 ; 7 lines to move
LDIR ; copy the lines
LD C,$20 ; prepare to copy one line - 32 bytes.
LD A,H ; fetch the high byte of source
CP $50 ; is it in lower third ?
JR Z, CLINE ; exit if so to clear 15'th
; line to accept new text..
CP $49 ; if in middle third of screen
JR NC,SAME ; don't adjust source.
ADD A,7 ; but if destination is text line 7
LD H,A ; then adjust to point across a third.
LDIR ; copy 32 bytes across thirds.
SUB 7 ; restore source to top third again as
LD H,A ; there are more moves within third.
JR SLOOP ; back to scrolling loop.
SAME LDIR ; this briefly copies line 8 to 15.
; copying line 16 to 15 is harmless
; but looks awful.
JR SLOOP ; back to scrolling loop.
;====================
;
;This routine clears text line 15 which consists of eight pixel lines.
;
;====================
CLINE LD BC,$0800 ; set counter to 8, C to zero.
LD H,$48 ; high byte of initial screen address.
CLOOP1 LD L,$E0 ; all pixel lines have $E0 as start,
; and $FF as end.
CLOOP2 LD (HL),C ; insert a zero.
INC L ; address next horizontal byte
JR NZ,CLOOP2 ; loop until L is zero.
INC H ; address next vertical byte.
DJNZ CLOOP1 ; and repeat for all 8 lines,
; continuing to set print position.
; Set up print plot mask in the alternate accumulator.
LD A,$80 ; prepare plotting mask 10000000
EX AF,AF' ; save in alternate accumulator
LD A,$E0 ; start of line 15 is $E0
LD (PRIPOS),A ; set print position variable.
RET ; return.
;======================
;
; This is the PRINT routine which prints on line 15 only. The line must have
; been cleared previously. As the bitmaps are stored as vertical slices of
; a character and have to be laid down one pixel at a time, the
; routine 'plots' the characters onto the screen.
;
;======================
RITE LD C,6 ; prepare to advance 6 pixels for a
; space
CP 123 ; is character higher than 'z' ?
JR NC,UPD6 ; forward to update by six pixels
SUB 39 ; reduce to range 0 - 83 decimal
JR C,UPD6 ; forward to print as space if less
; than "'"
LD D,$56 ; high byte of character set start.
LD B,A ; multiply
RLC B ; by
ADD A,B ; three - max is 249 decimal.
ADD A,B ; five - max is 415 decimal
JR NC,RITE1 ; if last addition produced no carry
; skip to use $56 as high byte.
INC D ; else increment high byte in D to $57.
RITE1 LD E,A ; transfer low byte to E
LD B,$05 ; count five source bytes.
RITE2 LD HL,(PRIPOS) ; fetch screen address low byte.
LD H,$48 ; set high byte.
LD A,(DE) ; fetch a character bitmap.
INC DE ; address next source byte.
RITE3 RRCA ; is the bit set?
JR NC,RITE4 ; forward to leave corresponding
; screen pixel unset if not so.
EX AF,AF' ; switch in the 'plot' mask.
PUSH AF ; preserve it on machine stack.
OR (HL) ; combine with what's on the screen.
LD (HL),A ; and update screen address
POP AF ; restore mask.
EX AF,AF' ; and save for future use.
RITE4 INC H ; advance vertically down the screen.
BIT 4,H ; when high byte reaches $50 then this
; program is about to be overwritten.
JR Z,RITE3 ; otherwise loop for all 8 bits.
CALL UPD1 ; update mask and possibly the low
; byte of screen address.
DJNZ RITE2 ; repeat for all 5 vertical slices.
; then continue into update routine to create a 1 pixel gap between characters.
;===================
;
; The update routine modifies the plotting mask rotating by a single pixel
; if C holds 1 but by 6 pixels if C holds 6. The screen address may be
; incremented.
; The routine is also entered at UPD6 with C holding 6 to print a space.
;
;===================
UPD1 LD C,$01 ; update by 1 pixel.
; -->
UPD6 EX AF,AF' ; switch in mask.
ULOOP RRCA ; rotate mask to right.
JR NC,NOCHNG ; skip if no carry.
LD HL,PRIPOS ; address print position low.
INC (HL) ; and move to right.
NOCHNG DEC C ; decrement pixel counter.
JR NZ,ULOOP ; back to ULOOP for more.
EX AF,AF' ; save mask.
RET ; return.
; ----------------------------
; Routine to validate a keypress
; against a table of valid keys and
; loop until a meaningful key is pressed.
; ----------------------------
KEY PUSH HL ; save HL throughout.
KEY1 CALL KSCAN ; scan the keyboard.
LD HL,TABLE ; address keys table.
KLOOP CP (HL) ; compare key in A against an entry.
JR Z,FOUND ; forward with a match.
INC L ; address next table entry.
JR Z,KEY1 ; end of table so back to read the
; keyboard again
JR KLOOP ; loop back until table read.
; but a match is found so transfer low byte of address to A.
FOUND LD A,L ; transfer table location to A
CPL ; entries were in reverse order so
; complement to give translated value.
POP HL ; restore initial value of HL.
L55DA RET ; return.
; Note there is a gap of approx 18 unused bytes here.
; ---
; Of the 40 keys on the Spectrum keyboard, only nineteen are used by this
; program.
ORG $55ED
TABLE DEFB $25 ; Q
DEFB $0D ; R
DEFB $21 ; ENTER
DEFB $0E ; F
DEFB $15 ; E
DEFB $16 ; D
DEFB $0F ; C
DEFB $00 ; B
DEFB $26 ; A
DEFB $1B ; 9
DEFB $13 ; 8
DEFB $0B ; 7
DEFB $03 ; 6
DEFB $04 ; 5
DEFB $0C ; 4
DEFB $14 ; 3
DEFB $1C ; 2
DEFB $24 ; 1
L55FF DEFB $23 ; 0
; ---
ORG $5600
; The character set consists of characters 39d(') to 122d(z)
; Characters outside this range are printed blank.
; Some characters within this range have been intentionally left blank as they
; are not required by the disassembler and are unlikely to occur in text
; messages.
; Characters are stored as vertical slices so the letter A is
; 01111110 = 126
; 00001001 = 9
; 00001001 = 9
; 00001001 = 9
; 01111110 = 126
;CSET
DEFB 0,4,2,1,0 ; '
DEFB 0,28,34,65,0 ; (
DEFB 0,65,34,28,0 ; )
DEFB 0,0,0,0,0 ; *
DEFB 8,8,62,8,8 ; +
DEFB 0,80,48,0,0 ; ,
DEFB 8,8,8,8,8 ; -
DEFB 0,0,96,96,0 ; =
DEFB 0,0,0,0,0 ; /
DEFB 62,81,73,69,62 ; 0
DEFB 0,66,127,64,0 ; 1
DEFB 66,97,81,73,70 ; 2
DEFB 33,65,69,75,49 ; 3
DEFB 24,20,18,127,16 ; 4
DEFB 39,69,69,69,57 ; 5
DEFB 60,74,73,73,48 ; 6
DEFB 1,1,121,5,3 ; 7
DEFB 54,73,73,73,54 ; 8
DEFB 6,73,73,41,30 ; 9
DEFB 0,0,36,0,0 ; :
DEFB 0,64,50,0,0 ; ;
DEFB 0,0,0,0,0 ; <
DEFB 0,0,0,0,0 ; =
DEFB 0,0,0,0,0 ; >
DEFB 2,1,81,9,6 ; ?
DEFB 0,0,0,0,0 ; @
DEFB 126,9,9,9,126 ; A
DEFB 127,73,73,73,54 ; B
DEFB 62,65,65,65,34 ; C
DEFB 127,65,65,34,28 ; D
DEFB 127,73,73,73,65 ; E
DEFB 127,9,9,9,1 ; F
DEFB 62,65,73,73,122 ; G
DEFB 127,8,8,8,127 ; H
DEFB 0,65,127,65,0 ; I
DEFB 32,64,65,63,1 ; J
DEFB 127,12,18,33,64 ; K
DEFB 127,64,64,64,64 ; L
DEFB 127,2,12,2,127 ; M
DEFB 127,4,8,16,127 ; N
DEFB 62,65,65,65,62 ; O
DEFB 127,9,9,9,6 ; P
DEFB 62,65,113,193,62 ; Q
DEFB 127,9,25,41,70 ; R
DEFB 38,73,73,73,50 ; S
DEFB 1,1,127,1,1 ; T
DEFB 63,64,64,64,63 ; U
DEFB 7,24,96,24,7 ; V
DEFB 31,96,28,96,31 ; W
DEFB 99,20,8,20,99 ; X
DEFB 3,4,120,4,3 ; Y
DEFB 97,81,73,69,67 ; Z
DEFB 0,0,0,0,0 ; [
DEFB 0,0,0,0,0 ; /
DEFB 0,0,0,0,0 ; ]
DEFB 0,0,0,0,0 ; ^
DEFB 0,0,0,0,0 ; _
DEFB 0,0,0,0,0 ; uk currency symbol
DEFB 32,84,84,84,120 ; a
DEFB 126,72,72,72,48 ; b
DEFB 56,68,68,68,0 ; c
DEFB 48,72,72,72,126 ; d
DEFB 56,84,84,84,72 ; e
DEFB 0,124,10,2,0 ; f
DEFB 24,164,164,164,124 ; g
DEFB 126,8,8,8,112 ; h
DEFB 0,72,122,64,0 ; i
DEFB 64,128,128,122,0 ; j
DEFB 126,24,36,64,0 ; k
DEFB 0,62,64,64,0 ; l
DEFB 124,4,120,4,120 ; m
DEFB 124,4,4,4,120 ; n
DEFB 56,68,68,68,56 ; o
DEFB 252,36,36,36,24 ; p
DEFB 24,36,36,252,128 ; q
DEFB 120,4,4,4,0 ; r
DEFB 72,84,84,84,32 ; s
DEFB 4,62,68,64,0 ; t
DEFB 60,64,64,64,60 ; u
DEFB 12,48,64,48,12 ; v
DEFB 60,64,56,64,60 ; w
DEFB 68,40,16,40,68 ; x
DEFB 28,160,160,160,124 ; y
DEFB 68,100,84,76,68 ; z
; End of font.
;=====================
;
; This routine first prints the message ROMx then continues into the
; big print routine.
;
;=====================
ROMTXT LD DE,$50FC ; address ROMx
CALL CLINE ; clear line 15.
RLOOP LD A,(DE) ; fetch a character.
CALL CHROP ; print it on line 15.
INC E ; point to next character
JR NZ,RLOOP ; and loop until 4 characters printed.
; continue into big print routine.
; Routine to scan text at start of line 15
; producing big text in lower third of screen
; by updating colour attributes.
BIGPR LD HL,$5A20 ; attribute address for line 17 decimal
LD D,$48 ; display file address of line 15 top.
LD BC,$0001 ; colour in B starts as black ink on
; black paper (0).
; C is used as an eight counter.
BIGPR2 LD E,$E0 ; low byte of address in display file.
BIGPR3 LD A,(DE) ; fetch a display file byte.
BIGPR4 RLCA ; rotate bits to carry
LD (HL),63 ; load attributes with white/white.
JR NC,BIGPR5 ; if no carry leave as it is.
LD (HL),B ; else overwrite attribute byte with
; a colour.
BIGPR5 INC L ; point to next attribute byte
RLC C ; rotate the eight counter.
JR NC,BIGPR4 ; loop back for all eight bits
INC E ; bump the screen address
BIT 2,E ; check that bytes don't exceed 4
JR Z,BIGPR3 ; loop back for bytes $E0-$E3.
LD A,9 ; now manipulate the colour attribute
ADD A,B ; to give a rainbow gradation.
AND $1F ; but pure colours are hard to see as
LD B,A ; they get lighter so this compromise
; was arrived at by accident.
INC D ; move vertically down display file.
BIT 3,D ; check high byte to ensure still
JR NZ,BIGPR2 ; within middle third and continue.
RET ; return when all 7 pixel lines have
; been enlarged.
;=====================
;
; The keyboard scanning routine is similar to
; that in the Spectrum ROM at address $028E
;
; For each of the 40 keys a number in the range
; 0-39 ($00-$27) is returned.
;
;=====================
KSCAN LD DE,$FF2F ; initialize D to receive key.
; E is starting key value + 8
; $27 is 39 decimal.
LD BC,$FEFE ; commencing port address
; B is also an 8 counter.
KLINE IN A,(C) ; read a keyboard half row.
CPL ; pressed keys now equate to a set bit.
AND $1F ; isolate lower meaningful 5 bits.
JR Z,KDONE ; forward if no keys pressed in half-
; row.
INC D ; test D - result should be zero.
JR NZ,KSCAN ; two keys are unacceptable so start
; from the beginning again.
LD H,A ; transfer bit to H
LD A,E ; key value to A.
KBITS SUB 8 ; subtract eight from value
SRL H ; shift bit to carry
JR NC,KBITS ; loop until carry is set
JR NZ,KSCAN ; if two keys pressed in the same
; row then start again.
LD D,A ; otherwise pass key value to D
; and continue to check that no other
; key is pressed in other rows.
KDONE DEC E ; decrease starting key value for
; a new row.
RLC B ; form next port address.
JR C,KLINE ; repeat for all 8 rows while a carry
; is set.
LD A,D ; transfer key value to A
INC D ; test for a valid key in D/A
JR Z,KSCAN ; repeat from beginning if was $FF.
L57FE RET ; return with key value $00 - $27 in A.
; ---
ORG $57FF
DEFB 56 ; white/white 63 but it helps to use
; black/white 56 while testing.
; Note the above attribute
; which immediately
; precedes the attr.file
; is used to flood the
; screen with white/white before
; the return to BASIC.
; Normally this file builds a 2K object file
; e.g. tasm -80 -b u3.asm
; This can be loaded into the Z80 emulator using the extra functions
; Load a Block of memory/screen
; Set start to #4000, length to #0800 and name to u3.obj or whatever.
; execute with PRINT USR 16384.
; Since not all emulators can
; load an arbitrary block of code, by removing the semicolon from
; the start of the next two lines and building with
; tasm -80 -b -f38 u3.asm
; then a binary file of 6912 bytes will be produced which can be
; renamed to u3.scr which loads into most emulators.
; This will have black and white stripes in the lower two thirds of
; the display which may be cleared from basic. To highlight the ascii
; column in cyan, say, use PRINT AT 15,28; PAPER 5; " " .
;
; This file is difficult to work on, but I have now removed the self-modifying
; code that was present in the original version.
; .org $5aff+$1000
; .byte $38
.END ; cross-assembler directive