> I've been using 1/(2*pi*R*C) to determine the PIC frequency using an RC
> oscillator circuit.  Not being an EE, I'm not sure if this is entirely
> correct, but it seems to be in agreement with what I see happening with
the
> PIC when I use it in my application.

1/(2*Pi*R*C) is the frequency at which the magnitude of the impedence of the
resistor and capacitor match.  In most circuits, this is therefore roughly
the frequency at which "things start to happen" either above or below that
frequency.  At much higher frequencies, the capacitor looks like a short
compared to the resistor, and at much lower frequencies the capacitor looks
like an open circuit compared to the resistor.  This is also the "rolloff"
frequency of a simple R-C filter.  However, this will only give you a rough
idea of the likely frequency of an unknown oscillator circuit.  There is no
guarantee that the circuit is designed to oscillate at that point.


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