What caps are you sorrounding the xtal with?

-----Original Message-----
From:   David Schmidt [SMTP:dschmidt@RAIN.ORG]
Sent:   Tuesday, October 14, 1997 12:55 PM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        (OT, sort of)Crystals oscillating at 3x marked freq

Have a problem with a circuit occasionally oscillating at
3X the crystal speed.  It is a DTMF decoder IC (Motorola MC145436) directly
connected to a parallel resonant crystal with a 1M resistor in parallel.

Thought it was a problem with a specific brand of xtal, but another brand is
doing it too.  The oscillator may start up fine and be on freq, but other times
it doesn't.  If it does start fine, I can 'force' it to go 3X by momentarily
touching the
PC traces for the xtal.

Does overdriving an xtal cause it to oscillate at 3X?  Perhaps I need to add
a series
resistor?

PCB is spotlessly clean.  Traces are short and fat.
Any help/insight is appreciated.  Thanks
Dave