> I always thought a ceramic resonator works on the SAW principle (or
> compression wave) using a disturbance structure to set the frequency.

As does a crystal. They are both mechanical resonance devices. The
RLC "components" are analogous (?) to the mechanical properties
damping, mass and compliance.

> > To use a crystal at the series resonant point you must provide an
> > amplifier with the 360 degree phase shift needed.
>
> This is correct, but it somehow works for me. It is possible that there is
> enough phase shift in the oscillator and stray capacitances to allow
> enough gain nevertheless.

[.. quote rearranged]

> BTW the other commonly used two-inverter oscillator (LS, HC, CMOS
> etc) is a series oscillating one too.

What seems to work for you ? Earlier you were talking of leaving off
the capacitors on a PIC oscillator. Now you refer to two-inverter
oscillators. One inverter = parallel mode, Two = series mode.

> And the 1M5 resistor I usually use for this is
> too low to allow parallel mode imho. I went down to 220K without
> stopping the oscillation with this, at 5V, with PIC16C54XT and JW in
> XT mode. The pi caps were connected when I went down to 220K.

A typical crystal has an ESR at resonance of <100 ohms. The influence
of the feedback resistor is minimal once oscillation has started so
it can actually be quite low. Startup is a different situation and
the resistor needs to be high enough that the first signs of life
from the crystal will overdrive the signal from the resistor.

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: steveb@tla.co.nz      fax +64 9 820-1929
======================================================