Sinclair ZX80 / ZX81 / Z88 Forums

Quick update for what it's worth...

Crap happens... My personal circumstance has changed somewhat.

Project on hold until further notice.

Regards Andy

Don't hold your breath as nothing may come of it.. but currently in talks with a third party who is interested in producing some UDG4ZxPand boards.

Andy

Long time posting in this thread, I have purchased a set of stickers as mentioned in This Thread I'm going to try the non ZX81 stickers on some contoured keycaps from an old keyboard and see how they look. if they are alright i'll use the zx81 stickers, otherwise i'll use the zx81 stickers on the fl...

Paul wrote: ↑Fri Oct 06, 2023 8:30 am Maybe inside the CPLD?

yes this probably, heck if your already soldering half a dozen extra wires for additional features, changing your rom to a faster one, and possibly your ram ( whoever is still using internal 1 or 2K ) then heck a few more wires ain't gonna hurt.

Andy

Paul wrote: ↑Thu Oct 05, 2023 6:16 am My guess is he wants to short R28

Remove completly.

You mean either side of R28… One side is connected to the ULA. The other side is connected to the edge-connector and (on a standard machine) to the ROM. But I presume on a modified machine, the output of the OR gate will drive the ROM instead. Because the OR gate has one input directly connected to...

OK I think I was right the first time lol

if I take the romcs at the edge connector ( with a pull down resistor) to one input of an OR gate and the other input from the ula generated ROMCS and the output directly to the internal ROM.

that will work right?

A question for the technical minded... does anybody know of any external device that uses the ROMCS signal at the edge connector in any way other than to override the internal ROM? reason I ask, with fasr enough cpu, ram and rom in the zx81 13Mhz is possible. ( without zxpand connected ) with zxpand...

@Andy You say 70ns ROM for Big Bang, I assume ,after seeing your video that, this is a custom chip? its just a at28hc64b-70su eeprom but SOIC on a SOIC to DIP adapter board. a regular DIP eeprom of the same speed should work.. slower chips should work but because all that stupid resistors bridges t...

1024MAK wrote: ↑Mon Sep 25, 2023 11:54 pm Would now be a bad time to suggest 6X

Mark

I've got one of those.... the 20Mhz Zeddy... normal speed is slightly fast at 3.33Mhz

It is anything but a standard zeddy, ask Moggy...