genome <jtroxas <at> gmail.com> writes:

> 
> hello..
> Is it possible to drive 2 or 3 PIC's with only one crystal in HS+PLL mode to 
> operate them on the same frequency.. If so.. how may one do this?.
> 
> I read somewhere in some microchip appnotes... if I remember... that there 
> is an inverting amplifier inside the pic that causes the crystal to oscilate 
> the output of that amp is in osc2.. and input on osc1, something to do wth 
> the amp producing a 180degrees phase shift.. maybe somebody could explain 
> it.. this is why I'm having trouble the amp in the PIC is part of the 
> oscilator not just the crystal... is this correct?????? 
> 

The datasheet, at least for the 16F877A confirms what you are saying.  You can 
provide clock signal to osc1 input only and leave osc2 open.  I am not sure 
that adding more PICs to the osc2 output of another will work because you might 
overload osc2.  For stability, you can either use a buffer, or, better yet, use 
a separate crystal oscillator and drive all PICs from the same source.

Sergey Dryga
http://beaglerobotics.com


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