PS/2 Keyboard Adapter for FM77AV40SX – an exercise in remote debugging

When collecting old computers, one issue that comes up from time to time is that you’re missing the one piece that you need to get the machine working. Or you have the piece and it’s beyond your ability to repair.
Keyboards are often the culprit. I’ve gotten a few machines with keyboards where the foam pads under the keys had deteriorated enough to prevent the key presses from registering. There are ways to restore the keyboards by getting new foam and laboriously cutting new pads for the keys, but sometimes you just want to get to it and play with your old computer without spending weeks shaving pieces of foam.

PS/2 keyboards are in plentiful supply and are fairly simple to interface with a micro controller. Often with a bit of work they can be adapted to work with a variety of old machines.

I recently saw a post on the Vintage Computer Forum from a guy in Vancouver who needed a keyboard adapter to use a PS/2 keyboard with a Fujitsu FM77AV40SX that was missing its original keyboard. I was interested in helping out, since I had some experience building a PS/2 to ASCII converter to use a digital group computer.
But one wrinkle was that I did not have access to the computer, so debugging any adapter would be a bit of a challenge.

Coming up is an account of an exercise in remote debugging using a protoboard with an AVR microcontroller, equipped with a serial port bootloader. It’s a thrill a minute I tell ya.
Hopefully this will help out collectors of Fujitsu computers who are missing their keyboards! Stay tuned for more..

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