Sinclair ZX80 / ZX81 / Z88 Forums

XavSnap wrote: ↑Sat Dec 19, 2020 5:07 pm Kicad Project:

Thanks for the screenshots.

When I get time I want to get the 3D models right on most of the parts. I hope if anybody else has ideas they can start making use of the ZX21 project.

I am looking forward to getting it going. I may have some spare PCBs when I have finished. It is called the ZX21 for a reason I am not expecting to have it finished this year but I am hopeful for next year.

Well, we have PCBs and so far all the bits seem to fit the footprints.

I noticed this project and realized it had some similarities:
http://www.modularcircuits.com/blog/pro ... -computer/

Cheers Mark. The reason I asked is that I have a mind to make a miniature ZX80 and 81 using SMD components. And rather than use FPGA I'd rather use the real things, or as close to the real devices as possible. Out of interest what would be the closest modern device to use in place of the ROMs used ...

Well, the bits have turned up and the PCBs have been made and are in transit.

In the meantime, I have made this webpage to help with making the boards:
https://fordp2002.github.io/

Not quite. The /RAMCS signal goes low to enable the internal SRAM chip(s). But there is a resistor between the ULA (which does the address decoding) and the internal SRAM chip(s). The /RAMCS signal at the edge-connector is on the SRAM side of this resistor. So to disable the internal SRAM chip(s) y...

The internal RAM is disabled by shorting out of the RAM CS line to 5V which is on the edge connector. This does no harm to the ULA as there is a resistor.

Next stage buying the bits!

Slowly fixing issues.