RC Oscillator

There's charts in the data sheets, that show R/C and how the frequency
will vary with voltage.

and temperature.


 - Steve

... and tolerance of the components, and component behavior over changing
temps, and ...   The general point is that RC oscillation in this
context provides and approximate frequency.  Applications requiring
precise timing ought to use crystals instead.  For many things, though,
an RC oscillator is fine and it has the benefit of being able to clock
the PIC at frequencies well below those possible with a crystal.  This
is handy if you: a) Don't need an accurate time reference and b) Want
to reduce the PIC power consumption.  For example, I use an RC oscillator
in my keypad decoder (http://www.tundraware.com/Software/PIC/keypad /).