collapseos/recipes/rc2014/ps2
2019-06-29 11:18:37 -04:00
..
Makefile recipes/rc2014/pc2: new recipe (WIP) 2019-06-28 22:54:57 -04:00
ps2ctl.asm recipes/rc2014/ps2: implement scan code buffer 2019-06-29 11:18:37 -04:00
README.md recipes/rc2014/pc2: new recipe (WIP) 2019-06-28 22:54:57 -04:00

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.