collapseos/recipes/rc2014/ps2

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

After having built and flashed the glue.asm supplied with this recipe, you end up with a shell driven by the PS/2 keyboard (but it still outputs to ACIA).

There are still a few glitches, especially at initialization or at connect and disconnect, but it otherwise works rather well!