> I don't need precision. It can be 18 MHz, it can be 21 
> MHz. A ball park
> figure will do.

> Can you please suggest a resonator part number that I can 
> look up?

Gargoyle (OK, just this once, Google) is your friend.

And Digikey is often an immensely useful resource to start 
with

        www.digikey.com

They are often easier to access data sheets via than many of 
the datasheet sites. And they even sell stuff :-).

Typing

        resonator 20 mhz

in their search box returned

        http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=852887;keywords=resonator%2020%20mhz

with almost 40 listings for 20 Mhz resonators.

Also most useful is www.findchips .com
but Digikey often sufficeth.

If you use Gargoyle and Digikey first and then ask questions 
here with a bit of known background you'll find that the 
anciem curmudgeons here become much more helpful and even 
downright useful. People like Olin are world famous in 
Littleton Massachusetts for being grumpy and abrasive with 
people who don't seem to them to have done basic homework. 
(It's the seeming that matters :-) ). *However*, if people 
are seen to be trying then Olin and co are about the most 
stunning PIC resource you can have, bar none. Well worth 
cultivating. And there's mainly lurking Scott who seems to 
eat and breathe advanced algorithms and tricky ways of doing 
things better and faster and cheaper (choose any 3). If you 
can ever find a hard enough PIC problem to pose you may even 
tempt him out of lurk mode to answer.

Re resonators - if, after looking at eg the Digikey listings 
you decide that there are too many choices, then saying that 
you have looked at xxx but it's not obvious if there is a 
best choice, or what do people prefer etc, then people see 
you've had a good attempt at using the available resources 
and will usually fall over themselves to help.

Re PIC RC oscillator frequency - AFAIR (not having looked 
any time recently) the data sheets have a graph of frequency 
versus R & C combos.

You'll find this list a most valuable resource and an 
international community, well worth being part of.



regards


        Russell

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