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Following on from the previous article where I built a ZX81 on breadboard using the original chips and then modern equivalents of all but the irreplaceable ULA, I moved onto the next step, which was to replace the ULA. There are many alternative circuits on the next (I've already admitted I'm reinventing a wheel that's already been reinvented), however, the simplest circuit and a good starting point is actually the ZX80, so I started with that. There are rather a lot of chips required, so first I'm going to need a bigger breadboard. The one I had been using for many years seemed quite good, so I got another one of those to double the area. However, I took the opportunity took make a small improvement. The previous builds have taken power from the posts via wires to the top rails, and then via wires down the sides, and via smaller jumpers, across the top. Having all the rails separate does give increased flexibility, but pretty much everything I had built on there had been using the same 5V rails all wired together.
Grant Searle's ZX80 page).
To be continued......
UPDATE - I did just about get this working, but the breadboard version had some intermittent connections, so I didn't get much further with that. I have now revisited this and built a PCB version, a ZX80 clone I have called Minstrel.