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From: Fred Bloggs
User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
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Subject: Re: Querry, Kick Starting Crystal Oscilator.
Date: Wed, 13 Nov 2002 15:09:50 GMT
NNTP-Posting-Date: Wed, 13 Nov 2002 07:09:50 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Roy McCammon wrote:
> I've got a processor with a 32KHz crystal. The problem
> is that the crystal oscillator can take a l_o_n_g time
> to start and stabilize.
> My though is to build a 32KHz cmos schmidt trigger RC
> oscillator and feed that through a small capacitance into
> the input of the crystal oscillator to get it going.
> Any thoughts?
You should forget about playing games with the 32kHz crystal and go with
a 4.096MHz crystal driving a /128 prescalar into the processor. Since it
has been demonstrated that Q roughly sets the start-up time, and if
you notice that this is actually a number of cycles, then increasing the
frequency will decrease start-up time proportionately. A 4.096MHz should
be in full oscillation in 20ms. The increased power dissipation will be
negligible compared to the processor. If you survey some typical
oscillators such as at http://www.ecsxtal.com/surfosc.htm , then you
will see that the ~4MHz oscillators have a start-up time in the 4-30ms
range. The 4.096MHz crystal is readily available in several styles.
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