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NNTP-Posting-Date: Wed, 06 Nov 2002 16:34:15 -0600
From: "Dave VanHorn"
Subject: Re: Problems with cristal as clock for atmel AT90S8535
Date: Wed, 6 Nov 2002 17:32:28 -0500
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> At the moment i have a 8 Mhz cristal connected to X1 and X2 and two 22pF
> capacitors here a little ascii art to make it more clear:
You probably need to double up the cap sizes. The caps are in series, from
the point of view of the crystal.
> -----| 22pF
> X2 |-------|-------][---|
> | cristal 8Mhz |
> X1 |-------|-------][---|
> -----| 22pF |
Does the ground lead go directly, and only, to one of the 8535 ground pins?
> I used a hosonic 8Mhz b214 in a HC-49/U case.
> (it's a cristal in a metal case with two pins)
> I can not find any datasheet of it.
Not good, but it should still run.
> I tried to measure the cristal via a osciloscope.. but i think the signal
> to weak to measure.
> many schematics i see on internet i see have this construction.
Probe the xtal out pin only.
> so i assume the atmel has an amplifier build in for the cristal.
> I thougt the two small capacitors were there to make teh cristal osciliate
> out of it self and it did not need any extra signal to make a signal.
They are providing the load capacitance that the crystal needs.
> How does a cristal actualy work.. does it just make a sinus wave all the
> time out of itself?
Nope, but at 8 MHz, the phase shift through the crystal, with the right caps
in place, will be 180 degrees.
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