That's a cool piece of work. I spent a lot of time interfacing the Z80 (TRS80) to the outside world using both memory mapping and port IO. I Seem to recall (hell, it's been over 25 years), that the documentation stated that the OUT opcode put the lower 8 bits on the address bus, but in reality the whole 16 bits went out. Not sure if this was a documentation error or a Z80 bug. The Z80 had quite a few "undocumented" opcodes that could be used with care.
Yep, if you do "OUT (C),r", C goes to A0-A7 and B goes to A8-A15. 16 bit addressing!
I owned several TRS-80s (model I, III, IV), a Xerox 820 "Big Board", and a couple of Vector Graphics S-100 machines. All of them were lots of fun and I learned a ton.
