[Coco] Dragon to CoCo Conversion....

[Phill Harvey-Smith]

Quoting jdaggett at gate.net:

> On 17 Jan 2007 at 22:46, Chen Herzog wrote:
>
>> Would it be possible to patch ROM to do a virutal keyboard rewire, for
>> a true dual machine?
>>
>> Chen
> ************
>
> It is possible to patch the code but it will take a rather large   
> patch file. Better off to rewrite the KEYIN subroutine.

Yep, that's why I have gone the hardware route, it actually turns out simpler.
Couple of 4053s, mind I am having problems under the CoCo rom, due I  
believe to the 0.1uf caps on two of the lines that are related to the  
joystick buttons. Does anyone know why these are here, as they seem to  
be causing the key pulses from these lines to be "mishapen" and not  
recognised by the firmware, It does however reccognise all other  
keypresses. What I mean by mishapen is that the leading and trailing  
edge of the puls is almost virtical for the unaffected lines but  
curved for the ones with the caps on, I guess due to the  
charge/discharge of the caps.

Oddly the firmware in the Dragon rom does not have a problem with  
this, guess I just need to study the two keyboard routines and see  
what the difference is :)
or just cop out and use dip switches/jumpers instead :)

> Or even redo the older circuit that uses a MC68HC11E2 to convert PC PS2 scan
> codes to COCO keysrtoke values.  Since the MC68HC11E2 is discontinued, that
> makes that a bit more difficult. A PIC or and AVR could be used instead.

I have done this with an AVR and a Zarlink MT8816 crosspoint switch,  
works a treat, this sort of setup can with the correct translation  
table be used to replace pretty much any matrix keyboard, such as the  
one in the CoCo/Dragon.

Cheers.

Phill.

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