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'32768Hz capacitor values?'
1999\06\10@213336 by William K. Borsum

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>are you using a solderless breadboard? does it work ok with 4 mHz or
>other faster crystal?  ive never gotten a 33kHz to work with a
>solderless breadboard.  even if i solder the cap leads to the crystal
>and shorten the run to ground.  i have only gotten it to work with 30
>pf caps on a protoboard or pc board.  i think the breadboard's native
>capacitance more than 30 pf (i fiddled with reducing the cap size by
>5pf steps and never got it to oscillate).

Most interesting...
Just spent a half hour on the phone with a senior person at Microchip on
this same problem.  He apparently wrote the App-note on crystals, and says
to RAISE the capacitance rather than reducing it (assuming the layout
capacitance is reasonable to begin with).
He suggests 100 pF as an upper limit.

Also suggested injecting a sine wave into the Osc-In pin through a
resistor, and watching the phase inverted output from Osc-Out.  If it is
not 180 degrees out of phase, the something is seriously wrong with the
chip.  Also will tell you what the gain of the oscillator amp is by
comparing in and out amplitudes.

Still working this one--

Kelly

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William K. Borsum, P.E.
OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>

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