> could find highiest is about 20MHZ

I think the highest crystal you can use on OSC1-OSC2 with
an 18F is 25MHz

So if you want to run two or more PICs with the same 40MHz
you'll have to use an external clock. A crystal-locked TTL or
transistor oscillator/buffer is quite easy to make, or you could
use a 40MHz canned oscillator



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