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Thread: Multiple PIC's, one OSC.
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face BY : Richard Prosser email (remove spam text)



This came up a week or so ago & got me thinking.

1.      You should be able to feed 2 (or more) PICs from an external osc. or
even feeding the input side  of the second from the xtal drive (output) side
of the other. Possibly at the highest frequencies it may be dubious but in
the middle range I don't see why not.

2.      Q Cycle synchronising. With the PICs that have PWM output the Q
cycle is available (e.g. the '73s will produce a 10 bit resolution with the
LSB corresponding to a single oscillator cycle). Therefore, it should be
possible to use a PLL to synchronise the two clocks & processors down to
this level. You may need additional synchronisation to achieve an
approximate setting first but after that the Q cycle PLL could take over. As
you say, rise and fall times may need looking at carefully for actual
communication (along with port read/write timing) but it could be worth
looking at, particularly if in the case of parallel processing.

Anyone else any ideas on this?

Richard P


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