> A friend has started building a circuit with a 18F4550 and a 20 MHz 3 pin ceramic resonator.
> Is a resonator accurate enough to allow USB communication or does he need a quartz?

I did use a resonator in an early version of my pickit2 clone and did 
encounter some problems. I am not sure they were caused by the resonator 
but they might.

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Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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