At 09:32 AM 8/16/01 -0400, you wrote:
>Hi, I was wondering if there were any quirks that I should know of if I want
>to drive several PICs from the same clock ? A 20MHz ceramic resonator in
>this particular case. Can I simply run all the PICs clock inputs in parallel
>on the same resonator ? Somehow this doesn't feel wright, perhaps I should
>"regenerate" the clock at TTL level first ? I recall a circuit that did
>something like this on the MicroChip site but couldn't track it down...

If there is much distance (more than an inch or two with ground plane)
between the clock pins, it might be wise to buffer the clock output pin
using a single gate buffer. Here is one possbility, most of the
manufacturers have something similar:

http://www.fairchildsemi.com/ds/NC/NC7S32.pdf

One input to the clock OUT pin from the PIC with the crystal, decrease
the capacitor value by the input capacitance of the 7S32, and connect the
other input of the S32 to 0V. The output of the gate drives the other
PIC(s) using the external clock circuit (clock OUT open, input to clock IN).

If you have the room, a 74HC32 will be a bit cheaper (0.19 vs. 0.39 US/100pcs)

Or, use a packaged oscillator, which is guaranteed to work, as someone just
mentioned.

Best regards,
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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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