[Coco] overdrive ...

[KnudsenMJ at aol.com]

In a message dated 4/25/05 2:43:03 PM Eastern Daylight Time,  
kevdig at hypersurf.com writes:

>    I know you can't just hook them together, but  wouldn't the design of 
>the interface/bridge be simplified if you did  not have to deal with the 
>two clocks being  asynchronous?



As a retired hardware designer, I agree that whatever scheme is used  between 
the two CPUs, it will work better if the clocks are synchronized, so one  is 
an integer multiple of the other.
 
Otherwise, there will always be a "gray area" where some flip-flop is being  
set by one side just as it is read by the other, and strange things will 
happen  now and then.
 
Also, synchronizing the clocks means that all noise and cross-talk events  
will be repeatable, meaning you have a chance at debugging them.
 
So your 68K sidecar should pick up the Coco's E/Q clocks and phase-lock to  
them.
(Running *almost exactly* the same frequency, so the two clocks "beat"  
slowly, is guaranteed to stir up troubles -- so phase-lock 'em).
 
And of course, with the 68K running at a harmonic of the NTSC frequency,  you 
have the ability to run video hardware off the 68K side, if you ever want  
fast graphics.
--Mike K.