Adam,

Add a 5 to 10pf cap between the OSCIN side of the resonator and ground.
You say when you touch the input
With your meter probe, the PIC starts running.  This is because you've
added some capacitance to the curcuit
and unbalanced it enough that it starts reliably.   I've had to do this
a few times before.  Usually when I 
Use a ceramic resonator, I get the type that doesn't have the built in
caps.   I put discrete caps in the 
Circuit and I make one of them a few pf higher than the other so that
the OSC will start reliably.

 
Regards,

 
Jim   

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
Of Adam stambler
Sent: Friday, December 08, 2006 11:04 AM
To: Microcontroller discussion list - Public.
Subject: [PIC] Oscilator Problem

Hi, I was wondering if anyone could provide some oscillator guidance.  I
am trying to run a 16f690 off a 20 mgherz ceramic resonator with built
in capacitors.

I think i have all my my programming correct, but when I go to turn it
on, it does not work.  The oscillator does not start up.  However, if I
try to measure the voltage with my multimeter and touch the Clock input
pin, the PIC starts to work.  There is about 2.3V on the clock output
and input pin .

Right now i have a 1 mega Ohm resistor across the input and output leads
of the resonator like the datasheet said for it to have. I am running
the resonator in HS mode.

My guess is that my programming is correct but there is not enough drive
to get the oscillator going.  Unfortunately, I have no idea about how to
fix the problem.  This is my first oscillator circuit which I am using
for a school project.

Anyone have any ideas?

Thanks,
Adam Stambler
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