Here's a short video describing a technique to program the Z80 port for the TX pin on the Z80-MBC2. ALSO TI-85's? Bad Editing and I say 'Ah' & 'Um' a lot
source code:
https://drive.google.com/file/d/1Riqj...
Z80-MBC2:
https://hackaday.io/project/159973-z8...
PiGFX:
https://github.com/fbergama/pigfx