piclist 2002\09\13\171331a >
Thread: Monitoring internal clock?
www.piclist.com/techref/microchip/time.htm?key=clock
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face BY : M. Adam Davis email (remove spam text)



From my brief overview you are limited by no extra pins, and it uses an
RC oscillator.

Your options, to get 10%, is to replace the resister and capacitor with
1% or better parts (prefereably parts which are not affected by
temperature by more than 1% for a total of 4% maximum out of range), or
remove them entirely, cut the extra osc trace (if it goes anywhere) and
add a surface mount resonator either directly to the traces (if space
and layout permits) or with the adition of one or more wires and a dab
of epoxy to fix it to the board.

In order to get the software to detect whether it's in range or not you
must have a steady reference to compare it to.  There's nothing in the
explanations you've made which could act as such a reference.  Perhaps
if you tell us what the PIC is connected to we could come up with a
system in software.  the PIC has nothing intrinsically which could act
as a reference, but you might be surprised at what types of already
attached hardware could be made into a reference.

Lastly, can you calibrate them before putting them to use?  If you
calibrate each device before use so you know the temp coefficient of the
RC oscillator and the temp coefficient of the WDT, you may be able to
solve the three variable equation which would give you temperature and
thus the speed of the RC oscillator.  Chances are the curves will be
quite close, though, so you may not be able to obtain any useful data,
especially considereing that the RC and WDT could easily be at slightly
different temperatures.

-Adam

Tony Pan wrote:

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<3D8254E1.7050203@ubasics.com> 7BIT

See also: www.piclist.com/techref/microchip/time.htm?key=clock
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