> At 05:28 PM 2/17/01 -0500, jhancock wrote:
> >What value of resistor should be used in the clock leads?  Is this for
> >isolation of the pic clocks?
>
> No, there's no need to isolate them. It's for EMI control.
>
> You're talking about feeding a track a signal with edges that have energy
> up through 500 MHz.
> Adding some fixed resistance on the source end cuts down on the EMI quite
a
> bit, by slowing down the risetimes.
> Check the PIC spec, but I know you don't need that fast a rise time.
Stands
> to reason, if it can take a crystal input, which is nearly a sine, then it
> can probably take a pretty much slowed down square wave.
>
> The resistors should all be on the driving end of the tracks, not the pic
end.
> As to value, if you have a scope, then as much as you can take.
> If no scope, start out at about 100 ohms, and see what that does for you.
>
I have not tried this with a PIC so please don't flame me if you
try it and it doesn't work or if you are one of the Guru's and I am
missing something really obvious.

Why not configure one PIC as a xtal osc and connect a gate to the oscillator
output to act as a buffer for distribution of the clock signal to the other
PIC's

By the way you may care to look at

http://www.microchip.com/download/appnote/category/articles/fact001.pdf

which is entitled "Basic PIC16/17 Oscillator Design" on the last page (4)
there is a note on External Clocks, and quote

"For really power stingy applications, with high speed external clocks
approaching 20MHz, the device will draw less power if the clock is injected
at the osc-out pin ............."

Regards

Chris

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