Yesterday I surprised myself by managing to dump half the ZX81 ROM by wiring it up to the Tl866ii as a 2732 instead of a 2364 (which the TL claims ignorance of and I can’t hack it in because the firmware is encrypted).

I say half because I should have been targeting the 2764 but got confused because the 32 is pin compatible (a DIP24 instead of DIP28) but I honestly wasn’t expecting my method to work so it’s a huge success and I know what I need to do to get the rest.

I was surprised when I didn’t get a dump of 0xffffs and even more surprised when the data wasn’t garbage and actually disassembled to Z80 assembler!

Starting to look like the ROM isn’t the reason it won’t boot which is kinda exciting!

This is the current status quo for the - got some cheapo keycaps on it and it works like a charm! Got the kit ready to crimp some more sturdy dupont cables with a bit more length on them and replace the angled headers with straight ones and a ROM chip flashing setup on the way so I can start screwing around with the "OS".

I've additionally been using it with the 16K RAM pack with no problem so the 32K RAM upgrade can go on the backburner for a bit seeing as I've got some headroom to play with!

Also had a go at loading from a line-out cable but I think I need to do some experimentation with levels to get that working.

Today I asked the ZX81 to tell me about itself.

Strictly speaking what I said was:

10 PRINT CHR$ (RND*255);
20 GOTO 10

This is how it felt about the subject.

Being able to talk to it after all these years is strangely cathartic.

Oh shit son!

Looks like the keyboard design was a success (apart from not completing the trace from the bottom row and having to hand-patch it)!

Guess I gotta figure out how to attach it then :P

The ZX81 keyboard PCBs show up on Monday and I finally found an eBay seller that does PCB mount cherry clones (Gaterons) on the cheap so I got 40 of them on the way from China.

The upcycled machine will be called the Grimmclair ZX87. Fingers crossed the PCB works!

TIL my ZX81 doesn’t even have enough RAM to map a single Linux memory page even before all the memory mapping overhead.

Good enough start for today. I decided against making it reversible seeing as this is my first real PCB. Should be able to take two of these and daisy-chain them for a full ZX81 keyboard map.

I think I'm going to add some mounting holes, some decorative silk-screen and then send them off to get fabbed. Then all I need to do is buy some headers and PCB mount switches, desolder the shitty ZX81 keyboard connector from the motherboard and it should be all ready to build when it arrives.

Then I can figure out how the hell I'm going to mount the thing!

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