William Chops Westfield wrote:
> I'm curious.  Why do you expect the PICs internal (RC, right?) clock
> to be more stable than an external (555 based, and still RC) clock?
> I thought on-chip resistors and caps tended to be a bit LESS stable
> than (good) discrete parts...

First, the OP is running his PIC from a 20MHz crystal.  Second, some of the
newer PICs show oscillator accuracy to within 2.5% over the full temperature
range.  That would be very hard to do with a 555 since its period is
proportional to a capacitance value.  Even the older PICs could guarantee
about 7% over the full range if I remember right.  It wouldn't be easy to
find a capacitor with that accuracy and stability from 0-70degC.


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