[Coco] Checking/Testing a 68B09P

[Mike Pepe]

jdaggett at gate.net wrote:
> On 2 Jul 2007 at 11:06, Frank Pittel wrote:
> 
>> Other then doing it because you can. Is there a reason why a person
>> would want to build an interface to allow the use of a MC68B09 in a
>> Coco? The cost of building such an interface must certainly exceed the
>> cost of an "off the shelf" chip that could be used without any
>> modification.
>>
>> This is a serious question.
>>
>> Frank
> ****************
> 
> Only serious reason that I would consider it is to take advantage of the MC68B09 
> DMA function. Outside that there is no other reason than one could do it.
> 
> james 
> 

Hey James,

Yeah, although the DMA function would be hard to implement as well. Far 
easier in the CoCo to just TSC/HALT the thing and hijack the bus for DMA.

I'm not sure what you're pondering to make sure the internal E and Q 
clocks are in sync with the E/Q generated by the SAM (or GIME). 
Generating or hijacking a 4x clock signal to be fed into the extal pin 
is relatively simple. However guaranteeing that the phase relationship 
between the internally generated E/Q and what the SAM is feeding as E/Q 
is extremely critical. My guess would be that you can gate the 4x clock 
input to the CPU until the phase relationship on E and Q match and then 
let it loose.

Agreed with Frank though, there's really no practical reason to do 
something like this, but it's interesting to speculate if and how it 
could be done!