Search found 32 matches
- Fri Dec 16, 2016 7:45 pm
- Forum: Development
- Topic: 20Mhz ZX81 clone...
- Replies: 20
- Views: 10582
Re: 20Mhz ZX81 clone...
Hi fella's, So..., anyhow, whats involved in making zeddy go at 20Meg.?, I can think of something straight away, the hsync and vsync will require a 12bit counting chain, but what about any(if any) rom timing constants go? Maybe a requirement to switch between clocks on the fly like from 40MHz to 6.5...
- Wed Dec 07, 2016 5:59 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
Correct.PokeMon wrote: I assume this is a clock polarity mismatch (falling/rising edge) of the video clock (6.5 MHz).
- Wed Dec 07, 2016 3:50 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
Hi Fella's, Wow!, I didn't notice the cursor shifted to the right but it is, I did notice that on the chess game the pieces were slightly unsymmetrical anyhow it just so happened it was an easy fix. Thanks for bringing it to my attention. :D In between there was another problem which cropped up, I w...
- Mon Dec 05, 2016 7:27 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
Hi All, More good news, I've just loaded my first commercial game CHESS and it is working. :D Retrotechie, about that AND gate with the inverted input?, PokeMon is right, what happens is on the plot screen you get flickerin on the display so you need it. So heres my line up, total chip count =7 and ...
- Mon Dec 05, 2016 6:23 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
After much head scratching across the entire weekend and today, I think I have reached my objective.I had to include another d-type flip flop to Retrotechie's design around the line counter reset. http://i571.photobucket.com/albums/ss156/onecommie/IMG_0243_zpsv4nbgq3o.jpg http://i571.photobucket.com...
- Sat Dec 03, 2016 1:28 am
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
PokeMon, I love your avatar, it makes me feel like life is in a cartoon and why should it not be with backup, that said, I took heed of your post and went for the hsync generator, starting at 200 counts and ending somewhere around 207 one step at a time. This cleared the zig zag on the top right han...
- Sat Dec 03, 2016 1:05 am
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
- Fri Dec 02, 2016 4:45 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
http://i571.photobucket.com/albums/ss156/onecommie/IMG_0237_zpscaommptf.jpg http://i571.photobucket.com/albums/ss156/onecommie/7921726e-fd73-493b-a7f5-150ad2ce4cf1_zpss2bonnua.jpg http://i571.photobucket.com/albums/ss156/onecommie/IMG_0234_zpsnhiu8atw.jpg http://i571.photobucket.com/albums/ss156/on...
- Thu Dec 01, 2016 9:34 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
from Wilf Rigter Hi PokeMon, Nice interesting circuit that you have brought to the forum attention, thanks for that. I tested the two bjt latch and it does indeed work very well. Now my zx81 prototype boots straight into slow mode and I can switch from slow to fast mode and back again using just th...
- Wed Nov 30, 2016 11:19 pm
- Forum: Development
- Topic: ZX81 ULA-in-a-CPLD
- Replies: 238
- Views: 124034
Re: ZX81 ULA-in-a-CPLD
Are you sure that the transistor actually switches off fast enough? Actually, you are right, with the transistor removed completely from circuit there is no change in screen characteristics in slow mode. :oops: I've tried a very wide range of resistor/cap. values and the best result I can get is wi...