I'm designing a board with an ATXmega8E5 and an ATmega328p. It will have some wireless interfaces and stepper motor controls.
I pretend to use an external capacitor to get best clock accuracy. Reading about it for both I came with the following:
C1, C2 with recommend value of 10pF for 16MHz.
C1, C2 with recommend value of 12pF-22pF for 16MHz.
I also read an atmel note that give the formula to calc capacitance load as:
C = 2*Cl - Cstray where Cs vary from 5pF to 10pF.
Reading more about it on the internet the Cs value should be arounf 5pF.
So in the case of ATXmega8E5 it gives 10 = 2*Cl - 5 <=> Cl = 15/2 =~ 8pF;
For ATmega328p it gives 12 = 2*Cl - 5 <=> Cl =17/2 =~ 9pF;
So am I ok to use the same crystal with CL=8pF for both?
There is anything else that I take a look at?