What the title says 
Here’s the link. Post by Dave Curran .
I have been expanding the instruction manual for my Minstrel ZX80 Clone to include more information on how the ZX80 works. I thought it would be good to expand on that even more here. So, how does the ZX80 work?
Well, the first thing to know about the ZX80 is that, unlike most other computers, it’s main job is not to run your code. That’s very much a side task. The thing it spends most of it’s time doing is drawing a picture on the TV screen. And it does that be executing mainly NOP instructions.
Unlike most other computers of it’s era, it doesn’t have a video chip. It doesn’t have any custom chips in fact. There is a Z80 CPU, a 4K ROM chip, and two 1K x 4 bit RAM chips, and seventeen 74 series TTL chips, and that’s it.