On Sun, May 08, 2005 at 01:23:51PM +0100, Dave Turner wrote:
> Hi,
> 
> I have recently made a clock program in assembler.  I have tested it
> with the SIM and the stopwatch, and it is about 0.000041 seconds out
> every 2 seconds.  When i download it onto the PIC though, it is a
> visible amount out - I have it next to an accurate clock here, and it
> can get as far out as half a second every 2 minutes.  I am using the
> 16F87's internal oscillator, running at 8MHz.  I have checked the
> datasheet for the 16F87, and it says the internal oscillator is +- 1%
> accurate, I think, at 25 degrees C.  I think something must be very
> wrong for it go get that far out.

Do the calculation - half a second in 2 minutes is 0.4%, well in spec.
You'll need to use a crystal to keep accurate time.

Cheers,

Chris
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