by Paul Robson
"This grew out of my unreleased Spectrum Emulator, as did my Jupiter Ace emulator. (I'm going backwards in time...) I got quite fascinated with the extraordinary hardware of the ZX81 and decided to hack my Z80 engine to emulate a ZX81. Large chunks of the code were nicked from my other emulators, (you may recognise them if you've played with the Ace emulator). It works quite happily with the ZX80's ROM,and the Assembler ROM AszMic.
"What's different about this one ? Well, its free, its got a built in debugger, it's fairly quick (say about 1/3 speed of XtenderF) - but it was never designed to go like a train. All the Z80 Registers are stored in RAM, and the display is emulated correctly. There is a hack for standard screens to speed display rendering up, but it still works through the standard code if you want. And it is completely free.
"I could make it faster but why ? - it's fast enough. On my Cyrix P120 it goes nippily rather than insanely, flat out things run quick rather than as a blur. This'll mean it probably needs a 486SX-25 ish for full speed, ATs and things are out.
"It does have some improvements over the shareware xtenderf .. (for example "Zombies" works properly and the keyboard works correctly) and ts1000 (the copy I had was a bit erratic ?). Hires seems to work ok. I've tried the Steve McDonald Games, Wilf's 16k and 1k programs & they seem to work ok.
"The only program that didn't work correctly was 'Chess' which has some copy protection on the front. Towards the end of the protection an NMI is generated without the display being setup, which makes it go haywire. A few 'P' files didn't work, but did work after being Loaded into Xtender and then Saved again.
"The source code is also available, if you want it."
ZX81 for MS-DOS [Homepage]