A note on Keyboard interfaces

Jim Brain brain at jbrain.com
Sun Jan 6 23:33:16 CST 2008

For those with machines that have a way to plug into the KB matrix and 
want PS/2 keyboard support, I would suggest a derivative of C=Key 
(www.jbrain.com/vicug/gallery/c=key/).  It acts like an 8x12 keyboard 
matrix to a vintage machine, no modifications to the machine are 
needed.  As currently laid out, it's designed to work with the CBM 
VIC/64/128 series machines, but the source has been structured to allow 
easy retargeting to any KB matrix up to 8x12.  On the PS/2 side, it 
decodes all incoming data and can send data to the PS/2 keyboard, such 
as resetting the KB and setting indicator LEDs.

And, source code is under GPL, as is the design.  I'm always up for a 
donation if you like the work, but I was once a starving collector too.

The key is the MT8812 (or equivalent) cross point switch.

However, it's overkill if you just need a serial or parallel output 
(PS2Encoder is much simpler).

Note that, if you just need a PS2 KB to vintage machine interface, C=Key 
can be reduced in size and a much smaller uC can be used (you only need 
8 data lines to run the Xpoint switch, 2 for the PS/2 interface, so a 14 
pin or 20 pin uC will work fine.  That's the same for the PS2Encoder.  I 
used a 28 pin IC in the design as that was handy, but the design can 
work the smaller units.

I'd be happy to help folks design new variations on the design for other 
systems (Atari and TI come to mind).


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