AVR-Chat

The 18pF crystals are what's known as Parallel Resonant, and the
Series ones are what's known as Series Resonant. It has to do with how
you connect a load capacitance to the crystal to get it to oscillate.

The important thing is, for microcontrollers, you want Parallel Resonant.

Note that a 18 pF crystal is NOT used with 18 pF capacitors - you need
to do a little math to figure out how to size the loading capacitors.
There's information available on this in
http://www.avrfreaks.net/index.php?module=FreaksArticles&func=downloadArticle&id=21

-Randy

On Wed, Oct 22, 2008 at 7:45 PM, Brian <blue_eagle74@yahoo.com> wrote:
> I was looking at Jameco for crystals. Under impedance is says 18pf and
> series. What is the difference on how they are hooked up to a uC?
>
> Brian
>
>