AVR-Chat

At 07:44 PM 11/20/2003 +0000, nangkon wrote:

>I saw a lot of schematics that use 2 capacitors with 
>crystal that is connected to XTAL. Is there a way
>to determine the appropriate values of capacitors?
>
>Do I need to use some equipments to do that? Or is
>there a general rule somewhere?

There used to be a page on this.. Back when I had web hosting :)

Use a crystal specified for parallel operation. It will have a loading cap spec.

Take the crystal's specified load capacitance.  (22pF typical)
Double it (44pF)
Subtract 5pF for the parasitics in the circuit (39pF)

Use two 39pF caps in this case. 
Without measuring the parasitics, or a shortwave receiver to get the crystal's exact frequency, this will get you pretty close.