-----Original Message-----
From: Larry Bradley [mailto:lhbradley@IGS.NET]
Sent: Wednesday, 23 April 2003 5:30 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: CCP compare function


I'm trying to use the CCP module on a 628 to generate 10ms interrupts. =
I've
done this before using timer1, preloading it with a value then reloading =
in
the interrupt routine. It works, but I thought I would try it with the =
CCP
module, since it isn't necessary to keep reloading the timer in the
interrupt routine.

Using a 20 mHz xtal, setting the CCP registers to 50,000 should generate =
an
interrupt every 10 msec. I use the interrupt to accumulate hours, mins =
and
seconds for  a time-of-day clocks. When I compare the time from the PIC
with the time from my GPS, over about 14 hours, my time is about 7 =
seconds
too fast. Changing the CCP value to 50007 makes the clock track the GPS
time just fine.

The xtal is a nominal 25 ppm device - this could account for 1 or 2 =
counts
in 50000, but not 7, I wouldn't think

Has anyone else played with timer1 and the CCP in this fashion?

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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