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Thread: XTAL startup issues on PIC 73B
www.piclist.com/techref/microchip/time.htm?key=xtal
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face BY : stouchton@capitaresearch.com



Primarily, all crystals are different, and all oscillator circuits are
different.  If these differences line up the wrong way, no oscillation.
Most manufacturers of oscillator circuits never fully characterize its
parameters at wafer level, and unknown variances go into the marketplace. I
went around and around with Microchip on this one several years ago, and
could not find one engineer that could state exactly what the crystal
specifications are.  They primarily spec'd load capacitance, but this is
only a small part of the crystal spec.  Equally important is the loss of the
crystal (Rs).

Here is a trick that worked for me with RF Microdevices:   Contact the
crystal manufacturers and let them know what you are up to.  After
contacting about 10 of them, I lucked onto the people that supplied the
original spec to RFMD for their design spec (Bomar Crystal).  you might get
lucky too.



ALSO:   Power supply is critical for xtal startup / run.  Make sure your DC
is reaaaaal good.  Make sure you have a GOOD decoupling cap, and limit lead
length.  (High quality ceramic, short heavy leads, avoid 90 degree bends).
Harmonics running around on the supply seem to really effect the PIC's
oscillator circuit.


My bet is that the Rs spec on your xtal is marginal.  If you have a network
analyzer (or spectrum analyzer, or scope and sig gen) you can compare good
to bad xtals and determine what spec is pushing the limit.  I would first
primarily focus on the loss through the xtal.

{Original Message removed}
<NEBBIBHANCGGPMLFJMMIKENOCGAA.stouchton@capitaresearch.com> 7bit

In reply to: <00bb01bfd20e$ab14b7a0$c48a6dc2@xs4all.nl>
See also: www.piclist.com/techref/microchip/time.htm?key=xtal
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Subject (change) XTAL startup issues on PIC 73B

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