ZX81 ULA-in-a-CPLD

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
McKlaud
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Re: ZX81 ULA-in-a-CPLD

Post by McKlaud »

No /IORQ, no /NMI ...
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Andy Rea
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Re: ZX81 ULA-in-a-CPLD

Post by 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
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overCLK
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Re: ZX81 ULA-in-a-CPLD

Post by overCLK »

Andy Rea wrote: Sat Nov 10, 2018 9:23 pm 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
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1024MAK
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Re: ZX81 ULA-in-a-CPLD

Post by 1024MAK »

ZX81 ROM disassembly/ recreated source code available here ;)

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AndyP
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Re: ZX81 ULA-in-a-CPLD

Post by 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

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1024MAK
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Re: ZX81 ULA-in-a-CPLD

Post by 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
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
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AndyP
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Re: ZX81 ULA-in-a-CPLD

Post by 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
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Re: ZX81 ULA-in-a-CPLD

Post by amazingco »

AndyP wrote: Sun May 16, 2021 7:18 pm 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?
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mrtinb
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Re: ZX81 ULA-in-a-CPLD

Post by 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
Martin
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ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
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