=20
> The PIC18F4550 and siblings have a PLL with a prescaler. The
> input to the PLL must always be 4MHz

I've used the 4550 a few times and know its oscillator block. My
query was whether the board crystal can be swapped for another
if serial comms (not USB) was Bill's priority and error rates with
the 20MHz were unacceptable. As you've shown though he can
get close enough
--=20
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