Search found 54 matches

by zx81user
Mon Apr 15, 2013 4:29 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62527

Re: ZX81 ULA-in-a-CPLD

Thanks again for the detailed description! Yes, if people want to try this themselves, I suggest to do a good study of the ZX80 schematic first. Then, understanding the CPLD circuit as drawn by RetroTechie, although slightly different, is easy to follow. Now, I would like to see the same circuit but...
by zx81user
Sat Apr 13, 2013 9:17 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62527

Re: ZX81 ULA-in-a-CPLD

Hi,

I am interested into looking at this CPLD ULA design, can I download it from somewhere?

Best regards,
Michel
by zx81user
Wed Apr 10, 2013 8:34 am
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Re: Bring Zeddy back to life

The reason for the high power signal is that it is simply feeded directly into the ULA with TTL gates. So need something about 1.5 or 1.6 Volts to recognize a high. That's the simple trick. The output was adapted to very sensitive microphones connected to cassette recorders. There is a simple devid...
by zx81user
Wed Apr 10, 2013 8:26 am
Forum: Hardware
Topic: ZX81 I/O interface for your projects
Replies: 27
Views: 8763

ZX81 I/O interface for your projects

I mentioned in some other thread that I used to have an I/O interface that had 8 TTL inputs and 8 TTL outputs. It was a board that came together with a book called "20 Simple electronic projects for the ZX 81 and other computers". Now, I don't have this interface no more but I still have the board l...
by zx81user
Tue Apr 09, 2013 11:13 pm
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Re: Bring Zeddy back to life

Woohoo! Another one back to life :D Congratulations! If you find the schematic/layout for the IO PCB I might be tempted to make one or two..! C I'll start a new thread for this interface, nearly finished drawing the schematic and PCB layout. If there is enough interest, I'll order some boards. Michel
by zx81user
Tue Apr 09, 2013 11:09 pm
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Re: Bring Zeddy back to life

I tried to write an own loader code which transfers databits more fast and not with a series of five or nine pulses. It is realized as a two stage loader, in the first part the new loader code is transferred with normal speed of about 38 chars/second. After transfer the loader is started as new pro...
by zx81user
Mon Apr 08, 2013 11:58 pm
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Re: Bring Zeddy back to life

Thanks guys, that is a big BINGO! I attatched a picture for your pleasure :-) You got to admit that the real thing is better than the emulator! I did go through all the problems listed, like swapping EAR and MIC (........ obvious mistake .........), using mono vs stereo cable etc etc. But then, yest...
by zx81user
Mon Apr 08, 2013 10:36 am
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Re: Bring Zeddy back to life

No, the screen won't change at all. I mean, I see the usual un-synchronized lines after I type "load", but they don't change once the audio comes in. It seems like the ULA doesn't detect anything at it's input.
by zx81user
Mon Apr 08, 2013 5:16 am
Forum: Hardware
Topic: Bring Zeddy back to life
Replies: 17
Views: 2912

Bring Zeddy back to life

Hi everyone, While cleaning out the garage, I found my Zeddy that had been in a box stowed away for about 25 years or so. I decided to bring it back to life in the past couple of days. So far it's going quite well. I could only hook it up to my Compro DVB-T300 TV card as that is the only TV tuner I ...
by zx81user
Tue Mar 26, 2013 1:54 am
Forum: Development
Topic: timing interrupt routine
Replies: 10
Views: 2166

Re: timing interrupt routine

This should work! in your mainprogram LD IX,mycode mycode CALL #281 ; the normal IX routine myprog NOP end CALL #292 CALL #220 LD IX,mycode JP #2A4 I don't follow this reasoning completely. Since the interrupt routine is called twice, I need to know in my routine if I need to call address #281 or #...