William K. Borsum wrote:
>
> Greetings ALL:
> Does anyone out there have practical experience (I've already read all the app
-notes, talked to the FAI's, the factory techs, etc. etc ad nauseum.) with getti
ng 32.768 KHz watch crystals to start reliably with the PIC's?
>
> I'm working primarily with 508/9's and 54's. In the case of the 509's and '54'
s, I have a circuit in production that works perfectly, repeatably, and starts e
very time--HOWEVER when I plug in a 509B the oscillator doesn't. Ditto with the
54's--a stock 54 or 54A seems to work fine, the 54B's refuse to oscillate in the
 same circuit.
>
> I am using standard C type crystals from Digikey SE3202 (Epson C-002RX 32Khz 2
0PPM, 12.5 pF 30KOhms typ. series resistance)
> with 12 pF load caps in the standard two caps to ground configuration straight
 out of the data books and tech notes.
>
> QUESTION: has anyone else encountered this behavior? What did you do to fix it
?
> Thanks,
> Kelly
>

I had a similar experience with a PIC16C54
oscillator that worked fine and the identical
circuit with one of the PIC17Cxx wouldn't work.
It turned out the inverter had more gain in the 17
and was overdriving the watch crystal.  Try adding
between 100k and 500k in series with the crystal
on the output side of the osc. circuit.

Mark Walsh