On Sat, 09 Aug 2008 10:59:14 -0400, Spehro Pefhany
<speffSNIP@[EMAIL PROTECTED]
> wrote:
>On Sat, 09 Aug 2008 19:32:53 +0530, the renowned ClueLess
><clueless@[EMAIL PROTECTED]
> wrote:
>
>>For very slow crystals it is necessary to add a series resistance in the
crystal
>>circuit. How do you calculate its value with respect to the two
capacitors that
>>connect the crystal to the ground?
>
>The resistor is there to limit drive power.. so it depends on crystal
>characteristics (ESR, max drive power) and other things (drive
>voltage, load caps). It's not a straightforward calculation,
>particularly if you want to minimize power consumption and/or drive
>power. Overdriving the crystal can lead to excessive drift or failure.
>Typically 32kHz-ish crystals have *maximum* drive powers in the 1uW to
>100nW range.
Thanks for your response.
Actually the micro is running slower, say about 5%, than what it should (a
thirty second operation takes place in 31.5 seconds) so I was wondering
whether
the RC values have any bearing.
Perhaps I should try to change the C value by inserting a trimmer instead
of the
fixed cap.
Thanks again for your time and help
--
Thanks for your time and attention
ClueLess
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