AVR-Chat

I usually ask the vendor to find out what the crystal manufacturer suggest.
It does vary. The suggestions already posted here will probably work. If you
want to avoid the issue entirely, you can use an oscillator module that has
the necessary parts inside it. These devices usually have 4 pins on them,
power ground and output. Look online in the Digikey catalog. Make sure the
operating voltage matches your cpu supply voltage.

Al Welch

-----Original Message-----
From: nangkon [mailto:nangkon@yahoo.com]
Sent: Thursday, November 20, 2003 1:56 PM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] Re: General Question on crystal with capacitors


Thanks for your reply.

I am planing to use a 16Mhz crystal with an
atmega128 mcu. I saw some schematic use
some values, and some do not use cap at all.

I saw some crystal spec mentioning about
load cap. Does this value come into the
formulate somehow? What if I do not use
cap? What will happen?

I am pretty new to electronics. So when you
mention about parallel operation. What
do you mean? Outputing data to a port
for example?

thank you again

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:

>
> 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.



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