Sinclair ZX80 / ZX81 / Z88 Forums

It seems the chip crisis also affects the availability of the 27C256. If you can't find one, you can opt to use an 28C64, (8K x 8 EEPROM) available from Reichelt https://www.reichelt.nl/nl/nl/eeprom-64-kb-8-k-x-8-5-v-150-ns-pdip-28-28c64-150-p1946.html?&trstct=pol_2&nbc=1 yes, you need to change a w...

Currently the latest revision is rev 1.9, the last patches were pulldown resistors (10K, BASE to GND) on the 5 2N3904 transistors of the joystick interface. Also I fixed some component values in the cassette interface logic, the current BOM (and component placement diagram) have the correct values. ...

I shall continue testing it after I have connected my prototype keyboard. I heard that loading and saving does NOT lead to a crash, but will investigate this myself, and also If my fake loading-bar logic works as intended. After I am more or less finished I will start on designing a PSG expansion bo...

well, now I finally got my own copy working, you can see it working in this picture https://revspace.nl/kiekjes/photos/20220810/P1030221.JPG Not that to get it working I changed all the logic (which was originally a mix of LS and HC logic) to only HC logic, and I changed the inverter used by the cry...

I noticed there was no real BOM available on my GitHub pages for the ZX81+38, only an empty entry where the .ODF (open office spreadsheet) file should have been. I deleted the empty entry, and added the real .ODF spreadsheet file. Note that the spreadsheet lists exactly which component to buy from t...

Well, I checked and the keyboard gerber files can be found on the ZX81+35 section of my GitHub entry https://github.com/mahjongg2/ZX81plus35 The same keyboard can also be used for my later design the ZX81+38 use it together with the keyboard overlay .PDF, which when printed full size on an A5 sheet ...

Nice!

Thanks Mark. I'm managing...

in the meantime I have made a new layout and am now at revision 1,6, Details can be found at GitHub, and at www.revspace.nl in the projects section.

Due to corona, I still have not built a prototype board myself, but in the meantime several people are trying to get their version working, and a few small errors have cropped up. The main problem is that two address lines (A13 and A14) on the expansion connector have switched, so I have to repair t...