lp oscillator is not working perfectly

[vin]

Dear sir,

in my current project i am using a 32 kz crystal in LP mode. but it seems to be unstable.sometimes the oscillation is starting after 20-30 seconds. and in sometimes it oscillator goes to unstable state after some time. any one can suggest optimum values of capacitors and series resistance used with 32 khz crystal in LP mode with PIC 16f676 IC.

regards,
Vin

[Ttelmah]

You need to know exactly _what_ crystal. There are dozens of different specifications for a '32KHz crystal'...
The Q, ESR, etc., all differ between crystal models. In general, most 'watch crystals', have a load capacitance figure between 6, and 13pF, and C0, of below 2pF. However most should oscillate, just with reduced accuracy. The fact that you are having problems may suggest you have a type with perhaps have particulary high resistive losses in the crystal, or there is a problem with your board layout. The leads need to be short, and you should be careful to clean flux from round the crystal pads, or the parasitic loads may be high enough to prevent oscillation.

Best Wishes