[stevekemp]

You say it might be the same for the Z80? I think, happily, the situation there is a lot more open and well-documented.

There are specific sites such as http://z80.info which are good resources to describe the chip. The Z80 was also the main processor of a lot of computers, in the UK the Sinclair Spectrum sold in the millions, and there are an awful lot of coders who started their careers, or childhoods, playing with them. People of my age would be reasonably familiar with assembly and the things it can do.

The fact that the Z80 was also used in consoles also provides another avenue for information. There are a lot of emulators out there which have implementations if not necessarily good documentation.

(On a similar note there's a lot of legacy code out there, as the Z80 was one of the targets for CP/M, which is itself source-available these days.)

Compiling CP/M, Pascal, C, FORTH, and running BASIC on a z80 are all trivial - with the right supporting hardware/circuitry for I/O.