At 07:59 PM 10/06/1999 -0500, you wrote:
>    I was experimenting with a 32.768kHz crystal on my PIC to get "long,
accurate times" and found that it wouldn't work...I am connecting it to
both osc pins and then putting two 22pf capicitors to ground off of each
pin....  but it doesn't work.  Could it be the cap values?  if so, what
values should I use?  thanks...
>
>
>Jonathan Newport


Values may be different for different PIC-types and different for different
brands of crystals. In general, the larger the cap's the more
current is consumed, the more stable the osc. gets and the slower it starts.
By the way, it is voltage dependent also.-

Some brands of  watch crystals works well, others hardly at all in a specific
application. There seems to be two
types of cylindrical cans. By some reasons, larger cans seems easier to get
moving than smaller cans (but some surface mount crystals are fine!).

I would recommend you to experiment with caps and resistors and try test
start and
functioning over the whole range of possible supply voltage and temperatures
relevant for your stuff.

A safe set up for a midrange PIC may be:


              |--------|
-----osc0-----| 33K    |-----|
              |--------|     |
                             |
------osc1 ------|-|XTAL|----|
                 |           |
                 |           |
           47pf ---        ----  100pf
                ---        ----
                 |           |
                 |           |
        gnd    ------------------

This works well for Vsupply 3-5.5V.

Best luck,

Hans