[Coco] USB keyboard interface for CoCo

Steven Hirsch snhirsch at gmail.com
Thu Nov 29 21:05:00 EST 2012


On Thu, 29 Nov 2012, Phill Harvey-Smith wrote:

> 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.

Dana Peters' PS2-to-CoCo adapter (later sold by Cloud-9) used a crosspoint 
switch.  I once looked into building one from Dana's original plans, but 
ISTR that the Mitel MT88xx parts were not readily available.

Steve


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