Search found 170 matches

by mahjongg
Wed Dec 09, 2015 11:03 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

Here is is as a .PNG picture, right click on it to open it in another windows for full size view

This is ZX81+35 Revision 2.2
[attachment=0]ZX81+35 rev 2.2 schematic.png[/attachment]
by mahjongg
Wed Dec 09, 2015 10:52 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

I know, its a problem that is being worked on, if you have a Google Chrome browser it will work though.
I used one to upload the file.
I'm working on converting the file to a picture for upload here, and on Revspace.

P.S. It also works with IE, (yuk).
by mahjongg
Wed Dec 09, 2015 1:10 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

Great, I have a new schematic revision 2.2 of ZX81+35 ( 35 because it should be released in 2016, 35 years after 1981) the new .PDF can be downloaded here: https://revspace.nl/File:ZX81%2B35_REV_2.2.pdf I'm asking all interested parties to download it, and have a good look at it, and comment. Note t...
by mahjongg
Fri Dec 04, 2015 6:26 pm
Forum: Development
Topic: ZX81 / TS1000 handheld keyboard replacement
Replies: 4
Views: 1768

Re: ZX81 / TS1000 handheld keyboard replacement

Looks good, (yeah, I'm here these days). Perhaps the holes could have been a tad smaller, that would have looked a bit better, but well done. You could have pre-drilled the holes with a very small drill and used the perforated board as a guide, so the hole locations became a bit more precise, or per...
by mahjongg
Wed Dec 02, 2015 1:40 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

I have started the necessary changes (in the schematics). The current logic for sync, and porch will be removed, and replaced by something completely different, i'm still deliberating exactly what, for the mean time I have made some changes, and replaced both EXOR's in the design with single gate ve...
by mahjongg
Sun Nov 29, 2015 2:34 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

well the counter is (normally) reset to zero by the interrupt acknowledge (INTACK) signal so yes you do know "how to count the cycles", as you have to count relative to when the INTACK occurred. so on a system that has a counter that is reset by the INTACK, then when you say the "hsync starts exactl...
by mahjongg
Sat Nov 28, 2015 10:54 pm
Forum: Hardware
Topic: Curious solution on PAL/NTSC
Replies: 2
Views: 761

Re: Curious solution on PAL/NTSC

yes, the ZX81 logic reads the bit continuously during the generation of the video, its not read once and stored as a variable. so yes you can change the vertical line count on the fly.
by mahjongg
Sat Nov 28, 2015 10:24 pm
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

thanks, I actually already had both information sources in my library, and used them, but not for the hsync counter logic, which produced a hsync at the last 16 cycles of the 207 cycle counter, and a front porch during the first 16 counts, that is (originally) directly after the VSYNC pulse ended, o...
by mahjongg
Wed Nov 25, 2015 7:38 pm
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

Okay, I see I made a few terminology mistakes, when I said "front porch" I obviously meant "back porch", I often make that mistake, because in my "vision" the back porch is in front of the video, like a "porch" is in front of the house. So yes I do in fact meant the back porch, used by the VDU as a ...
by mahjongg
Wed Nov 25, 2015 1:46 am
Forum: Hardware
Topic: ZX81+35 Clone
Replies: 228
Views: 37145

Re: ZX81 Clone

Hello, I'm mahjongg the author of this ZX81 clone, thanks for looking at the schematics of it, and for the tip. If I understand it correctly the frame counter should not be reset/synchronised by the VSYNC signal, but by the interrupt acknowledgment (INTACK) signal which is /M1 AND /IORQ, meaning I n...