Oh! Thats an entirely different matter. The Z80 is very cool, many different versions to choose from. It benefits from a very regular machine code (simple register fields, 2- or 5-bit opcode field), you can memorize it in half an hour.
And its still used embedded. My son wrote a simulator for a Z80 version that's flying on Juno (Jupiter space mission). It was coupled with an FFT engine for processing ice-penetrating radar signals. Lots of fun. SpaceX was interested in him out of college, but that was mostly an IT position.
Anyway of all the embedded systems I've used, I am fondest of the Z80 architecture. Good choice!
One of my favorite Z80 clones was, I think, the Z800(?). It had several register sets you could explicitely switch between. For instance, one for the timer interrupt, one for the main thread, one for a serial thread. Hyperthreads, years before anybody else had them! But it never caught on.
