Originally Posted by bob4432
excellent, i am about done w/ what you posted - changed the caps for the crystal to 18pf per the ds but other than that, same as you posted
But I think 22pF is a better choice.
Cl = (22pF * 22 pF) / (22pF + 22pF) + Cs = 11pF + Cs.
Aiming for 18 pF, and with an estimated stray capacitance around 5 pF, that will give 16 pF.
The atmel design note suggests 5-10pF stray-capacitance which gives 17.5 pF using 2 x 22 pF load caps.
Using 2 x 18pF caps will give an estimated load-capacitance at 14pF (with 5 pF stray capacitance), which is a bit further from the suggested 18pF from datasheet.
Both should work, but a quick calculation suggests 22 pF or more.
Atmel design notes: