The Expandor Systems SOFT ROM for the Sinclair ZX Spectrum.

The SOFT ROM

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This is how it was done in the old days.
Before the arrival of Emulators and Cross-Assemblers.
The Expandor Systems SOFT ROM plugged into the Spectrum's Expansion port.
The two big chips are two 8K Ram chips.
The seemingly nonsensicle

FOR i = 0 TO 16383
POKE i, PEEK i
NEXT i

did the trick with the right switch settings and copied the ROM software sideways into RAM.

The four switches are left to right: WD/WE With WD, POKE pokes to ROM, with WE pokes to RAM.; SOFT/NORM With NORM, PEEK and theProgram Counter read from ROM. With SOFT, PEEK and the PC read from RAM.; RESET - a non destructive reset activates RST 0.; NMI - a debounced NMI switch.

Of course the NMI switch just did a reset unless you POKED Ram to alter the logic.

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Images

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