Why not add a watch crystal (32oddkHz) as the driver for tmr0?
VERY cheap and reasonably accurate.  And once added you find lots of uses
for it.

Bye.

-----Original Message-----
From: Hartung, Greg [mailto:ghartung@ADT.COM]
Sent: Thursday, 2 August 2001 7:54
To: PICLIST@MITVMA.MIT.EDU
Subject: T0CK for slow INT


   My ISR routine takes a very long time to service.  About 70ms, longer
than the lowest frequency I can engineer with the dividers on a 20Mhz
crystal (20m/4/65536=.  I would like to call the ISR on a nice even
frequency of 10hz so the sampling is easy and intuitive to graph later.  The
dividers will reduce by up to 65,536, so...  a crystal of 10x? or a 555 of
10x? or is there an easier way?  I don't think I can do it the traditional
way of just interrupting more often and keeping a counter because my ISR
will skip interrupts on certain iterations.  Olin suggested trimming my ISR
code, but everything there needs to get done before the next iteration, so
that doesn't seem like the solution.

   Greg Hartung

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