Xiaofan Chen wrote:
>> 6 - If I remember right, 20MHz crystal doesn't work with USB. Did
>> you read the datasheet before designing the circuit? I didn't think
>> so. Go read it.
>
> Now it is your turn to read the datasheet ...

Ah yes, you're right.  For some reason I thought the crystal had to be a
multiple of 8MHz, but I see that is incorrect.  Sorry for the confusion.

To use the full speed USB peripheral, you need a oscillator that can be
divided by 1, 2, 3, 4, 5, 6, 10, or 12 to get 4MHz.  That means the allowed
oscillator frequencies are 4, 8, 12, 16, 20, 24, 40, and 48 MHz.  Note that
the last two at least can't be achieved by just connecting a crystal to the
PIC.  They have to be clock signals derived elsewhere and fed directly into
the PIC.


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