ZX81 ULA-in-a-CPLD

[McKlaud]

No /IORQ, no /NMI ...

[Andy Rea]

what i wanna know is what the heck is the ~IORQ line doing after the nmi stops... what in the world would cause so many io instructions ?

how many lines has your logic analyser got ? i'm thinking about probing the entire data bus and ~m1 in addition to the other lines then you can decode the exact instruction prior to a failure

Andy

[overCLK]

what i wanna know is what the heck is the ~IORQ line doing after the nmi stops... what in the world would cause so many io instructions ?

how many lines has your logic analyser got ? i'm thinking about probing the entire data bus and ~m1 in addition to the other lines then you can decode the exact instruction prior to a failure

Only eight.

[1024MAK]

ZX81 ROM disassembly/ recreated source code available here

Mark

[AndyP]

I realise that this is a very old thread but, does anyone have any gerbers/schematics/pcbs/ lying around for any of the ULA replacements that use either Xilinx or Altera devices?

Thanks

AndyP

[1024MAK]

Have a read of this topic for all the publicly available information.

The ‘internal’ details of the other CPLD ULA versions are not publicly available as far as I know.

Mark

[AndyP]

Hi Mark,

Thanks, I'd already found them but was trying to be a lazy b*gg*r and not have to design my own pcb.

Not to worry, time to get Kicad updated once I've mastered CPLD design.

AndyP

[amazingco]

Hi Mark,

Thanks, I'd already found them but was trying to be a lazy b*gg*r and not have to design my own pcb.

Not to worry, time to get Kicad updated once I've mastered CPLD design.

AndyP

AndyP,
I would like to assemble some didactic ZX81 replicas for some children and teenagers who are starting in the computer world. Could you let me know if this ULA of yours will have Gerber available?

[mrtinb]

If you wan't a schematic of the ULA. Then look at Grant Searle's page about the ZX80. Here he has a schematic. The ULA in the ZX81 is just all the chips on the ZX80 put into 1 chip - the ULA. The ZX81 includes a NMI Generator as well, which you will find later on the page:

http://searle.x10host.com/zx80/zx80.html

Another project you can get a schematic of is the ZX81NU. This is "ZX81 No Ula".

https://forum.tlienhard.com/phpBB3/view ... 017#p11017