Sorry for the repeat post. Looks like your reply header didn't include the list.

Hi Bill, the Microchip Midrange Reference Manual (pg 2-18 in the 1997 manual) addresses this problem especially with 32k xtals. Sometimes the gain is too high (or too low) on the oscillator pins. A shunt resistor (one in series with the xtal)
or a feedback xtal across the OSC pins will provide a consistant startup.

The book doesn't say what value to use but a scope on the OSC2 should tell the story. The waveform should be clean and in the midrange of the rails. If clipping or squashed, you could have the xtal jumping to a harmonic or even damaging it.
Selecting a series resistor with the xtal should limit this.

If that fails, a feedback resistor across the OSC pins may help stabilize the xtal and aid in a more reliable startup.
The book also says that a startup could fail if "a low freq design, low voltage, high teperature, waking from sleep,
noisy environment" and a few others.

In discussing this exact problem with Microchip this week, they state that a feedback resistor shouldn't be necessary
under normal conditions but their spec doesn't address exactly what oscillator device is to be used so external resistors
may be required by the manufacturer of the oscillator device.

Also 33pf might be a little wimpy for 32khz. The book says something in the order of 68-100pf
Good luck.
Rick



wb6otg wrote:

> I'm using the PIC16C774 with a 32khz crystal on the timer1 oscillator.  The oscillator doesn't want to start unless I have a scope connected to the crystal.  Any ideas?
>
> I'm using a Citizen CM100 crystal, which I think is very similar to the Epson crystal called out in the PIC data sheet, with the 33pf capacitors recommended by microchip.  The fact that it starts with a scope attached tells me that the control bits for the oscillator are configured correctly.  One of the microchip data sheets suggested making the capacitor on the driven side of the oscillator larger than the other one.  I tried 66pf on the driven side, and 33pf on the other side and it still won't start reliably.
>
> Bill
>
> --
> http://www.piclist.com hint: The PICList is archived three different
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http://www.piclist.com hint: The PICList is archived three different
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