[Coco] Dual UART with FIFO Card for the CoCo

[afra at aurigae.demon.co.uk]

Quoting sales at gimechip.com:

> You have some really awesome stuff. I was about to embark on a PS/2  
> Keyboard Interface. Since you already have a keyboard adapter  
> available, I'll explain what I was thinking: I was going to design  
> an interface that plugged into the cartridge port - this way the  
> CoCo wouldn't even have to be opened and it would not matter which  
> CoCo Model you have - the keyboard connector wouldn't matter. My  
> thinking was that whenever the CoCo made an attempt to access the  
> keyboard memory areas, the plug in cartridge would assert SLENB*  
> disabling the internal devices and replacing them with the circuitry  
> inside the keyboard interface cartridge.

The only problem that I can see with this is that the keyboard  
interface is implemented on one of the PIAs, whichon the CoCo 1/2 is  
also used to implement the bit-banger and on the Dragon is used to  
implement the paralell printer port, there may be other uses as I  
don't have the schematics infront of me currently.

So asserting SLENB/DSD would also disable those interfaces, unless you  
replicated their circuitry on your cartrige.

Incase you are interested one of the first things I designed was a  
PS/2 to Dragon keyboard interface, this used an ATMega16 (AVR) and an  
MT8816 crosspoint switch to replicate the switch matrix, theic of  
course can also be used on the CoCo as the only difference is that  
some of the keyboard rows are in a different place.

This design has the advantage that it can be used to replace pretty  
much any matrix keyboard up to the capacity of the crosspoint (16x8 in  
this case), I have used almost the same circuit to build a PS/2 to BBC  
Master Compact for someone in another retro group.

Cheers.

Phill.



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