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'[PIC] Monitoring internal clock?'
2002\09\12@152720 by Tony Pan

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Hi,

This is a duplicate message. But the previous one was sent without the
header.


I am writing an application, using internal oscillator.

I need to have very accurate timer. But I was told that the clock would
drift in time. Therefore I need to monitor the clock's frequency at the
beginning of the operation, if it drifts out of range, I would not start the
operation.

How do I monitor the internal clock frequency (in software alone)?

Thank you in advance.
Tony

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2002\09\12@155031 by

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Well, your software will "drift" along with the clock,
so that's hard. You software will never now the actual
"speed" of your clock, it can only count cycles but
never know how long a single cycle is, if it hasn't
some external reference to compare with.

Jan-Erik Söderholm.


Tony Pasd wrote:
How do I monitor the internal clock frequency (in software alone)?

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2002\09\12@160801 by Francisco Ares

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Tony Pan wrote:

>Hi,
>
>I am writing an application, using internal oscillator.
>
>...
>
>How do I monitor the internal clock frequency (in software alone)?
>
>

Software depends on clock, so the software itself is not sufficient to
check its own clock. You should have another external timing reference,
but if you would do it, I think that the best thing is to build a xtal
clock.

Francisco

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2002\09\12@193501 by Harold M Hallikainen

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On Thu, 12 Sep 2002 21:44:50 +0200
=?iso-8859-1?Q?Jan-erik_S=F6derholm_=28QAC=29?=
<.....Jan-erik.SoderholmKILLspamspam.....PAC.ERICSSON.SE> writes:
> Well, your software will "drift" along with the clock,
> so that's hard. You software will never now the actual
> "speed" of your clock, it can only count cycles but
> never know how long a single cycle is, if it hasn't
> some external reference to compare with.
>
> Jan-Erik Svderholm.
>
>
> Tony Pasd wrote:
> How do I monitor the internal clock frequency (in software alone)?
>

       I agree. The only way to determine the speed of the clock is to compare
it with a stable external reference. If you have a stable external
reference, you may as well just use it as the clock! You have a variety
of clock options available on the PIC, allowing you to balance clock
accuracy against cost.  These include (pretty much in order of increasing
cost and increasing accuracy):

internal RC
external RC
resonator
crystal
precision external oscillator (ovenized or temperature compensated)

Harold


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2002\09\17@100956 by rusque (Listas)

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Hello Tony,

> I need to have very accurate timer. But I was told that the clock would
> drift in time. Therefore I need to monitor the clock's frequency at the
> beginning of the operation, if it drifts out of range, I would not start
the
> operation.
> How do I monitor the internal clock frequency (in software alone)?

   if you have this device connected at the mains power, you can compare
the internal clock frequency with the mains frequency.

   Best regards,

   Brusque

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