> Ok, I've read AN826 from Microchip, and while informative... I'm still
> not sure whether I want a parallel or series resonant crystal, and if
> parallel does it really matter for basic circuits what the load cap
> value is (other than it be between 12 and 32 pF)??  I suspect series
> resonant will work, but can I get some advice from the pros on this
> one?

A few snips from my webpage (http://www.tla.co.nz/xtal1.html)
There's more there if you want it.
Otherwise (as someone already suggested) just plug in a 20MHz crstal
and a couple of 20pF caps and it will nearly always work.

Serial or Parallel resonance.
When a crystal is described as being a particular frequency series or
parallel resonant, it is analogous to any other part being specified at a
temperature of 20 or 25 degrees. The part is the same but the
frequency has been determined under those defined parameters.

Load capacitance
Once again, the crystal has been measured under the stated conditions.
In this case, the load capacitance and it is only relevant at parallel
resonance. If you use a different load capacitance, the crystal is in a
different situation from that stated on the can and will behave differently.
This may be a small shift in the frequency or may prevent the oscillator
from starting, depending on how far away from the stated value you
take it.

Steve.

==========================================
Steve Baldwin                          Electronic Product Design
TLA Microsystems Ltd             Microcontroller Specialists
PO Box 15-680, New Lynn                http://www.tla.co.nz
Auckland, New Zealand                     ph  +64 9 820-2221
email: steve@tla.co.nz                      fax +64 9 820-1929
=========================================

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