2pf caps to the xtall sometimes is good.
eXPerience !
Here is the linkie:
http://www.maxim-ic.com/appnotes.cfm/an_pk/58
Accuracy
The frequency accuracy of a crystal-based oscillator circuit is mainly dependent upon the accuracy of the crystal and the accuracy of the match between the crystal and the oscillator capacitive load. If the capacitive load is less than the crystal was designed for, the oscillator runs fast. If the capacitive load is greater than what the crystal was designed for, the oscillator runs slow.
In addition to the errors from the crystal and the load match, crystals vary from their base frequency as the ambient temperature changes. Dallas RTCs use "tuning fork" crystals, which exhibit an error over temperature, as shown in Figure 2. An error of 20ppm is equivalent to approximately 1 minute per month.
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Last edited by sayzer; - 6th October 2008 at 07:42.
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