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README.md
Interfacing a PS/2 keyboard
Serial connection through ACIA is nice, but you are probably plugging a modern computer on the other side of that ACIA, right? Let's go a step further away from those machines and drive a PS/2 keyboard directly!
Goal
Have a PS/2 keyboard drive the stdio input of the Collapse OS shell instead of the ACIA.
Status: work in progress
Gathering parts
- A RC2014 Classic that could install the base recipe
- A PS/2 keyboard. A USB keyboard + PS/2 adapter should work, but I haven't tried it yet.
- A PS/2 female connector. Not so readily available, at least not on digikey. I de-soldered mine from an old motherboard I had laying around.
- ATtiny85/45/25 (main MCU for the device)
- 74xx595 (shift register)
- 40106 inverter gates
- Diodes for
A*,IORQ,RO. - Proto board, RC2014 header pins, wires, IC sockets, etc.
- AVRA
Building the PS/2 interface
TODO. I have yet to draw presentable schematics. By reading ps2ctl.asm, you
might be able to guess how things are wired up.
It's rather straigtforward: the attiny reads serial data from PS/2 and then
sends it to the 595. The 595 is wired straight to D7:0 with its OE wired to
address selection + IORQ + RO
Using the PS/2 interface
As of now, the interface is incomplete and can only be queried through the
shell's iord. I've set my device up for addr 8 (that is, I wired A3
through the inverter, the rest through diodes, and hooked this pudding to OE).
When doing iord 8 in the shell, I get the scan code of the last key I pressed,
unless the 595 was "busy" with another code. For example, if I press A, my
next iord 8 will yield 1C (the "make" code for "A" in the PS/2 protocol).
Doing a second iord 8 right after a first will yield 0, indicating that the
device properly detect the first reading attempt and properly flushes the value
from the 595.