> -----Original Message-----
> From: Daniel Sweet [SMTP:daniel_sweet@NTLWORLD.COM]
> Sent: Wednesday, June 11, 2003 3:35 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC]: 3rd Overtone Crystal operation?
>
> Hi,
>
> 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.
>
> Thanks for your help.
> DAN
>
Check the datasheet again!  The PIC is not spec'd to run with anything
faster than a 25MHz crystal.  If you want to run the PIC at 40MHz without
using the internal PLL, you should use an external oscillator (e.g. a four
pin canned oscillator) to provide the clock.

Regards

Mike


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