Search found 32 matches

by commie
Mon Nov 21, 2016 10:56 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62449

Re: ZX81 ULA-in-a-CPLD

So then - what happens in detail ? As you said it is working in FAST mode. How do you enter FAST mode from system startup ? Usually it tries to switch on SLOW mode by default after RAM test. Did you force it anyway ? And what happens when you enter SLOW mode exactly ? Well, I have to boot with the ...
by commie
Mon Nov 21, 2016 6:46 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62449

Re: ZX81 ULA-in-a-CPLD

Hi Pokemon, I personally don't think it is glitches, I have read Retrotechie design report and it seems perhaps( I could be wrong) the design is incomplete which is a great shame because it works so well in fast mode. I have cross referenced the design with Grant Searl's zx80 slow mode adapter and t...
by commie
Sun Nov 20, 2016 6:36 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62449

Re: ZX81 ULA-in-a-CPLD

Can I just make it clear, everything works perfectly, the picture is rock steady there are no glitches or hic ups on the screen, all the scope waveform's look good no glitches. In fact, it's working so good I am contemplating building it on a pcb and using it as a basic language platform as is. Howe...
by commie
Sat Nov 19, 2016 10:09 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62449

Re: ZX81 ULA-in-a-CPLD

I might just add that I'm using retrotechie's Xilinix implementation and ported it over to the Atmel atf1504 plcc44. Well, I'm at a loss as to why it wont work in slow mode? Everything else including the tape load/save works perfectly, but only in fast mode.

cheers
commie
by commie
Sat Nov 19, 2016 4:55 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62449

Re: ZX81 ULA-in-a-CPLD

Hi Chaps, I've implemented the zx81 ula in an Atmel ATF1504 (plcc44) cpld and its working great except for one feature, that is it doesn't work in slow mode only fast mode with the nmi pin strapped high. When I connect the nmi I get garbage on the screen, but the nmi pulses are active as seen on my ...
by commie
Fri Feb 21, 2014 11:59 pm
Forum: Hardware
Topic: Replacement ZX80 Cases
Replies: 61
Views: 16311

Re: Replacement ZX80 Cases

No conspiracy at all :D You are welcome to make anything you like. Hi Paul, Okay Paul, I will let the board know how I get on. I'm currently about 65% complete, the thing is, when I write software for the avr, I do a little and get that small amount of code working, then code a little bit more and ...
by commie
Fri Feb 21, 2014 8:25 pm
Forum: Hardware
Topic: Replacement ZX80 Cases
Replies: 61
Views: 16311

Re: Replacement ZX80 Cases

Hi PokeMon, Are you suggesting new zx users should first build the zx80 and then modify it's hardware/software such that the end result is a functional zx81? No - I didn't suggest that. First you have to distinct between collectors and other users. Collectors mostly aren't interested in other stuff...
by commie
Fri Feb 21, 2014 5:24 pm
Forum: Hardware
Topic: Replacement ZX80 Cases
Replies: 61
Views: 16311

Re: Replacement ZX80 Cases

As Mark stated, this is just software. The ZX81 ROM is fully compatible to ZX80 and allows floating point math but only in FAST mode due to missing NMI generator - talked above. So the hardware is identical but smaller as all discrete logic was pushed into one chip (ULA) plus adding the NMI circuit...
by commie
Thu Feb 20, 2014 12:37 pm
Forum: Hardware
Topic: Replacement ZX80 Cases
Replies: 61
Views: 16311

Re: Replacement ZX80 Cases

In fact there is no big difference between ZX80 and ZX81. Hi PokeMon, For me, the big difference between the zx81 Vs zx80 is that the zx81 supports 32-bit floating point math whilst the zx80 only supports integer numbers. Sure, the zx80 is faster than than the zx81 but that is understandable, I'd r...
by commie
Wed Feb 19, 2014 9:47 pm
Forum: Hardware
Topic: Replacement ZX80 Cases
Replies: 61
Views: 16311

Re: Replacement ZX80 Cases

Hi Guys, Thought I'd just drop in for a chat, why bother with manufacturing zx80 cases?, yes I know what zx80 fetch on ebay but surely it would be make more sense to manufacture zx81 cases and pcb's. Lets face it, the zx81 is functionally a better micro than the zx80. My current plans are coding the...