About PIC crystals for time calculations
Use a 12.288 MHz or 9.830.500 Hz crystal- these result in integer results with suitable divider value.
12.228 MHz runs best with timer 0 interrupt, and 1:16 prescaler. /4096, results in 750 ticks/second.
They are perfect to generate 1 seconds timebase.
12.288 Mhz crystals are fine, or also 9.830.400 Hz.
There is no reason to employ complicate correction algorithms, which are needed for instance when using 8 MHz crystals.
Scrap from http://forum.allaboutcircuits.com/showthread.php?t=82034
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