Sinclair ZX80 / ZX81 / Z88 Forums

Thanks for those! I'll check 'm out... As for IO i think it is best to stick with the lower 3 bits A0-A2 used as partial decode only as in the original ULA, you will note that A2 doesn't acutally drive anything in the ULA but it is used by the ZXprinter. other IO's you choose to use yourself can of ...

RWAP wrote:(although the ZXvid is made redundant by this)!

Only very, very recently introduced, and it's already obsolete... What's the ZX81 world coming to?

As some of you will know I've managed to get an ULA replacement working stand-alone , and now that I'll clean up some of the logic in it, I'm wondering: Should I strive for 100% compatibility with original ZX81, or is it okay to make some improvements that you wouldn't notice with regular ZX81 softw...

TZX is usable by some emulators but not by real machines, though I expect there'll be tzx->wav players for loading IRL. Saving as 8 bit 11khz wavs might save some space, and I believe that MP3 will also work as long as the bitrate is high enough. These days people don't blink when downloading GB si...

Hello all! I just realized that the Sinclair ZX81 is about the only computer I know where "you see a screen (with characters)" directly equates to: "the Z80 CPU is functional", and: "the CPU is running (executing code)". And most probably, ROM & RAM too. This directly results from the intimate inter...

Went full steam ahead today, databit by databit completing force-NOP circuitry, keyboard inputs, and then disconnect that dataline from ULA. Until ULA was only outputting D6, A0', A1' and Z80 clock. At that point I updated the design to produce those signals as well, did some soldering & took the ju...

Thanks for that detailed post - that's great info for me to get on with. You're welcome. :) IMO the barrier to entry into programmable logic is pretty high, so I'm glad if I can help lower that barrier for someone. The more builders / developers, the more interesting projects around for others (inc...

Very Well done, it's no easy feat I know ! Still think my 74xx version was a Killer ! Yes very impressive - esp. that such a wire mess actually works... ;) If any of you have any pointers on getting started with the devices that you have been using, and best/cheap devices to use to do a "ULA" then ...

Whoohoo! Managed to grab some pattern data, and shift that out to the screen serially. Resulting in an actual recognizable image: ZX81 ULA development.jpg (what you see is entirely produced by the CPLD) Outer black is my TV, picture doesn't show it but on screen colors are nice bright white & black,...

I don't know where you can see this on the pictures of Grant because he did not show the RAMCS signal. I was guesstimating based on /MREQ low -> databus changing delay (assuming ULA logic responds quickly). Looks +/- 100 ns, which wouldn't be unreasonable response time for a RAM chip. If A15 is use...