Oscillator Selection

[mister_e]

Those USB PIC have a oscillator block that divide anything (well not on all mode but) down to 4MHz, then the internal PLL rise it up to 96Mhz, then you divide it /2 to have your expected 48MHz processor speed.

So why using 20MHz (or else) instead of 4? I no longer see of any good reason apart if, for some reason, you have a bunch of those already in stock.

[CocaColaKid]

The PIC that was are looking to use is the 18F2550. We don't need a many I/O, just a handful and a USB port. The only reason I could possibly think to use a faster oscillator is for better accuracy. Does it not make sense that to say an oscillator running at 4 MHz +/-50 ppm will be less accurate than one running at 20 MHz +/- 50 ppm due to multiplying less to achieve the same results?

[mister_e]

This is what i thought as well... but it's still divided down to 4MHz at the end... and you still have +/- 50 ppm at the end too.

We already talked about that here a while back

http://www.picbasic.co.uk/forum/show...5&postcount=11