> I am trying to run my PIC(18F252) at 40Mhz, which is locked to an
> external source using a PLL. I has this working with a 10MHz
> crystal using HS/PLL mode to give 40Mhz, but have had other
> issues with the HS/PLL so now want to run with HS mode
>
> The only 40Mhz crystals that I have been able to get hold of in a
> hurry have been 3rd Overtone mode ones. I only have a vague idea
> of what this means!
>
> Can anyone tell me how I make it run correctly in the 3rd
> overtone mode? Or direct me towards some information? I am
> assuming at the moment that the circuit arrangement needs
> changing slightly? I've googled and found a little info but not much.

        The only way to get that part running at 40MHz is with a 10MHz crystal and
PLL enabled, max crystal speed is speced at a maximum of 25MHz IIRC. Check
the datasheet. TTYL

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