Sinclair ZX80 / ZX81 / Z88 Forums

I'll answer my own question. Kelly Abrantes Murta on the ZX81 FB page suggested using the FRAMES system variable at 16436 and 16437 which is decremented with each image frame. I just used the lower address as this will be changing more quickly and worked just fine. If S is the seed, then S:=MEM(.164...

I'm looking for a random seed to feed a simple pseudo-random integer number generator I'm working on for Partial Pascal since the latter does not have a built-in RND function. Is there a good location in memory that is variable enough I could peek at for that purpose? Partial Pascal does have the ME...

How can I tell which ROM I have without opening up the machine?
Also, is there a drop in EPROM I can program to replace the ROM with a variant or there is a need for some form of EPROM adapter?

Thank you!
One question: will this modification affect the functionality of the ZXPand?

My board has a socketed SRAM chip. Is there a schematic of that mod so I can create an adapter?

I don't think the price point is too high at all. One is getting a brand new heavily upgraded computer with a proper keyboard and you could easily exceed 200 Euros trying to assemble all the vintage hardware required to match the specs presented here. In my view, the main target for this project is ...

Would love to see an updated manual. I have a project I'd like to use the Pascal package for, warts and all.

Call me a purist, but it just feels wrong to add color to a ZX-81. Part of the charm and quirkiness of that little computer is its lack of color.
To each his own I suppose...

I never found the games on early 80's computers to be particularly compelling as I was not much of an arcade game player, and so for the longest time the only games I owned were Video Chess and Scott Adams Adventure (on the TI 99/4A). I recall doing statistical analysis on lab data in TI Basic in co...

I wonder how many people used the ZX-81 for business purposes back in the day...