About the different ROMsīelow are the Roms. Because the memory from $C000 upward is used for the ZX Spectrum's display file, Paul Farrow's Roms cannot emulate a ZX81 expanded to full 48k ram. With every interrupt the display file of the ZX81 at $4000 is examined and a corresponding image at $C000 is drawn. Instead the possibility of the 128k Speccies to use a display file at $C000 is used. Because the ZX81 uses Ram at address $4000 for the display file, the Specci display cannot be located at this address too, because then you would see the bytes poked into the ZX81 display file on the Specci screen 'as is'. The screen update must be emulated, because the ZX81 has a completely different, character-based b&w only screen display. In fast mode the screen is blackened, and the interrupt routine does not draw the TV display, making the ZX81 running at full speed. Also the slow and fast mode is simulated. Even lots of high-res games work! You can choose from 4 memory setups, Screen, keyboard, printer and load/save routines are patched to work with the Specci hardware. These roms make a Specci run as a ZX81 at a very high degree of compatibility. If you are interested in using these cartridge for more than just testing and loading a ZX81 game, then you should visit his site. His page on these roms is very detailed and i will only summarize it in short here. Paul Farrows, has written some modified roms for the Sinclair Interface 2, ZX Spectrum and ZX Spectrum+ 128K and later 128K computers to emulate the ZX81 and ZX80. ZX81 Emulator Cartridges for Sinclair Interface 2 General description
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