ZX81 ULA-in-a-CPLD

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
McKlaud
Posts: 178
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Location: St Albans, UK

Re: ZX81 ULA-in-a-CPLD

Post by McKlaud » Sat Nov 10, 2018 9:20 pm

No /IORQ, no /NMI ...
Claudius
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Andy Rea
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Joined: Fri May 09, 2008 2:48 pm
Location: notts UK

Re: ZX81 ULA-in-a-CPLD

Post by Andy Rea » 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

Andy
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

overCLK
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Joined: Wed Nov 07, 2018 10:12 pm
Location: Spain

Re: ZX81 ULA-in-a-CPLD

Post by overCLK » Sun Nov 11, 2018 12:44 am

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
Only eight. :-(

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX81 ULA-in-a-CPLD

Post by 1024MAK » Sun Nov 11, 2018 1:14 am

ZX81 ROM disassembly/ recreated source code available here ;)

Mark

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