Search found 1610 matches

by Andy Rea
Mon Sep 04, 2023 1:53 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

With those free bits, could you offer faster turbo modes? This way we could try out up to which speed our Zeddy still works :mrgreen: You Want Quad speed ? in theory should work.. BUT you WILL need a faster CPU and The MOTOROLA type rom (or your own fast replacement ) the NEC roms dont even work at...
by Andy Rea
Mon Sep 04, 2023 1:53 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

what about just not allowing ROMCS to go low if ~WR is low ? would that work ? or would it need some address qualifier also like address <= $1FFF
by Andy Rea
Mon Sep 04, 2023 1:49 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

If we don’t find any better uses for spare bits, if there are spare output pins, maybe use for Blinkenlights :P This would normally be under software control, hence the Zeddy could gain a very simple output. If you don’t want a Blinkenlight, it could drive something else via suitable circuitry (tra...
by Andy Rea
Mon Sep 04, 2023 1:42 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

i forgot about fetching character data during the refresh when the screen is been drawn...
by Andy Rea
Mon Sep 04, 2023 1:38 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

And in case you are not short of macro cells: I would like to have a WR signal that doesn't come active in the lower 8K address space. So I could use a 32K Autostore RAM as combined ROM and RAM (RAMCS and ROMCS ORed) in order to have a three chip zeddy :geek: I once tried and it worked but could no...
by Andy Rea
Mon Sep 04, 2023 1:26 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

Paul wrote: Mon Sep 04, 2023 1:07 pm My ROMs are 45ns and my CPU 20MHz :ugeek:
That will be plenty fast :mrgreen:

I haven't done any calculations but can tell you that a 250ns eeprom ( at28c64-25pc) works okay
by Andy Rea
Mon Sep 04, 2023 12:49 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

With those free bits, could you offer faster turbo modes? This way we could try out up to which speed our Zeddy still works :mrgreen: You Want Quad speed ? in theory should work.. BUT you WILL need a faster CPU and The MOTOROLA type rom (or your own fast replacement ) the NEC roms dont even work at...
by Andy Rea
Sun Sep 03, 2023 7:32 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

Little update, pretty much proved the device works as expected, missed a pull up resitior off, and a capacitor LOL. i still plan to produce 2 versions, standard and enhanced Standard version plug in and go. composite video 1v p-p into a 75 Ohm load ( most tv's and monitors) Enhanced version will be ...
by Andy Rea
Sun Sep 03, 2023 12:32 pm
Forum: SALES
Topic: Swetland ZX81+38 Mechanical Keyboard PCB only - 3 available
Replies: 40
Views: 20369

Re: Swetland ZX81+38 Mechanical Keyboard PCB only - 3 available

If you want the Visio / OSD I can send it to you; I did think about changing the character set - just because I could - but decided to stick to as close to the original that I could find. Trev That would be awesome thank you. i don't have a colour printer so i thought i would get it printed as a ph...
by Andy Rea
Mon Aug 28, 2023 2:17 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97524

Re: Oh no! Not another ULA.

i think so i measure the gap between pcb's at 9.5 mm when the MK4 is mounted in a turned pin socket. the 1A 5v recoms are 7.5mm thick, but you might have to make it's leads a little longer. so that it cann lay on its back.

regards