[Coco] USB keyboard interface for CoCo

[Phill Harvey-Smith]

On 29/11/2012 15:18, Gustavo Ranaur Schoenaker wrote:
> The main problem is that the regular (e.g. non MEGA) arduino has 12 pins,
> two used by the serial port. The CoCo Keyboard uses 15 ports. My first try
> will be to use a MUX/DEMUX chip to to the job (and protect the precious
> CoCo PIC). If it doesn't work I would try to use the analog ports.

What I did in a similar situation was used a crosspoint switch between 
the AVR and the CoCo, one such as the MT8816A 16x8 switch available here :

http://www.futurlec.com/ICSFZarlink.shtml

This only needs 10 lines to drive it, you could probably get away with 8 
for a CoCo keyboard as you would only need 8x8, so the topmost bit on 
the X could be pulled high or low, and you could use a simple R-C array 
for the reset pin, that leaves you with 3 pins for X, 3 for Y, 1 for 
data (switch at XY open or closed), and one for write strobe.

This also has the advantage that the PIA in the CoCo will see it as an 
array of switches, just like the real keyboard.

Cheers.

Phill.