This is an expansion card for the Commander X16 retro PC, which exposes one memory mapped IO region (at a time) to a Glasgow Interface Explorer.
With it, the Glasgow can emulate nearly any IO card you might plug into the X16, so long as that card only wants to talk to a modern USB-capable PC 🤓. So far I've got an applet which half-assedly emulates a 16550, and hooks it up to a pseudoterminal on a Linux system. With David Murray's ROMTERM, you can then use the X16 as a "serial" terminal to log into the Linux system.
(To be super clear, that's all done without the Commander X16 Serial & ESP32 Network card.)
And here's a quick little video of it in operation: https://www.youtube.com/watch?v=3OkkUSMPfc0
The Glasgow has 16 IO pins. To act as an IO device, you need to handle:
- 8 data lines
- RWB
- PHI2
- At least one of the IO selection lines
- An IRQ
- Five address lines (for the full 32 byte space)
That's 17 lines. You could drop the IRQ line, but that'd be boring. Instead, we decode RWB, PHI2 and a jumper-chosen IO selection line using some 74-series logic, and condense the three of them into /RD and /WR lines. That fits everything into 16 pins.
mgetty -r -b -m '""' /dev/pts/X
not actually sure if the -b is necessary. The -m bit was the secret
sauce.