Jinx wrote...

>>  http://www.fairchildsemi.com/an/AN/AN-340.pdf
>
>Despite their attempts, I'm afraid it's still all a bit of a black
>art. The drivers in micros must be more complex than these
>parallel circuits, the type I've found so flakey. Do micros have
>AGC or some detector in them so they will operate over a
>wide range of frequencies ? For example, what is switched
>in/out when the micro is set to LP, XT or HS ?

Alas, it is indeed a black art.  I don't know what's being switched in
the PICs between LP, XT, and HS, but Intersil has a CMOS crystal
oscillator chip, the HA7210, that has a pair of frequency range select
inputs which change the internal biasing on the internal amplifier to
optimize its transconductance and power dissipation depending on the
operating frequency.  Perhaps PICs are similar?  (BTW, the HA7210 was
the first thing I thought of in response to your original question; but
it's only guaranteed to work up to 10 MHz.)

More coffee...

Dave

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