20 MHz + PLL vs 48MHz

[Demon]

... The PLL's VCO always runs at 96mhz. And the crystals frequency is always divided down to 4mhz for the PLL reference. So in effect, the frequency of the crystal doesn't matter, only it's tolerance....

DT

I noticed the division part, that makes a lot of sense. I just didn't know if there were other factors that would make a performance difference. So now I know that the tolerance is really what I'm concerned with when I'm selecting crystals.

I'll probably stick to 20 MHz components 'cause I've got lots in stock and I use them in other projects. But it is good to know that a 4 MHz crystal can be just as good for a 18F USB application.

Thanks guys!

Robert

[Dave]

Demon, Don't for get to view the power requirements for the the osc. circuit. The faster the crystal the more power it will draw. Although it sounds like you will be running it off the USB power, if it were to be battery powered this is something to consider.
Dave Purola,
N8NTA