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).

You will see, by typing on the keyboard, that it kinda works, but in a very basic and glitchy way. You will get double letters sometimes, and at some point, communications are likely to become "corrupted" (you reliably get the wrong letters). That's because parity checks, timeouts and reset procedures aren't implemented yet.

But still, it kinda works!