> The timing of the code (infamed by Myke Predko?) at the end of this mail
> simulates to the nearest µsecond using MPLAB.  However, when executed on
a
> P16F84 using a 4 MHz 3 pin resonator marked
> [4.00 (M x], I loose about 1 second every 10 minutes.  Same occurs at
> different supply voltages between 3.5 and 6V.
> 
> Presumably this is because of the +/-0.5% error (or greater) in the
crystal
> and my too frequent reliance on 1 microsecond being accurate?

Losing 1 second out of 10 minutes is an error of only 0.17%, which is well
within the accuracy rating of the typical ceramic resonator.  The obvious
solution would be to use a crystal, which is about 100 times more accurate
than a resonator.
        Jason Harper