16f628 internal oscillator

Started by hunt4it44 August 4, 2003
I did a little experiment this past weekend playing with the 16f628a-
04 and its internal oscillator. On one breadboard I put 2 16f628's
with identical clock programs that display on an LCD. The only
difference between the 2 16f628's was I set one up to use the
internal oscillator and the other had an external 4mHz oscillator w/
33 pf capacitors. The difference in the clock accuracy was
immediately apparent. I used the clock on my pc as a "control".
When I would power up my breadboard, the clock that was powered by
the internal oscillator was approx. 25% faster than the clock on my
pc. The clock that used an external oscillator was nearly identical
to the clock on my pc. It was slightly slower which I attribute to
the less than ideal construction on a breadboard.

I expected some difference but not that much. Does this surprise
anybody? Are any external capacitors required when using the
internal oscillator? Just curious.