Osborne 1 keyboard pinout

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Pin 1 is towards the top-right when looking at the front of the computer in the usual fashion. On the later '1a' model which I have, the plug on the coiled keyboard cable actually has 24 holes but the outer 4 do not mate with pins (it's not quite the same plug you find on a ribbon cable).

The Osborne 1 keyboard contains no electronics and does not require a power supply. The row and column lines connect directly to a matrix of keys. I believe that to read a row, the address is selected such that exactly one of the row outputs is driven low. Any pressed keys in that row will cause a zero to be read on the respective column line, while other column lines will be pulled up.

Pins 2-9 are driven by the system address bus through open-collector inverters. Pins 10-17 are pulled up to the system +5V supply by a 3.3K resistor pack, and buffered onto the system data bus when the processor reads the keyboard.

Pin 19 can be connected to the system +12V supply through J6 (a 2-pin link, open on my Rev. D PCB) and R21 (22 ohms).

I'm intending to build a PS/2 keyboard adapter using an ATtiny and a bunch of 74LS374's, as my keyboard was busted when I got it (eBay bargain).