||How do you determine the external capacitor values for the crystal?
The values for the external capacitors CL1 and CL2 depend on the crystal manufacturer's requirements.
The load capacitance (CL) can be determined as follows: CL = (C1*C2)/(C1+C2).
For example if C1 and C2 are 28pF, then CL value will be 14pF.
Note that the values for C1 and C2 should include the internal capacitances CP1 and CP2.