The crystal Spec is
- Frequency of 12.00 MHz +-2000 ppm
- In fundamental-mode operation
- Parallel resonant
- Effective series resistance of 30 ohms
- Power dissipation of 1 mW.
See the schematic found in C:\Cypress\USB\Hardware\EZ-USB Fx\DEVBD REVB\SCHEMATIC PDF'S for the EZ-USB FX and C:\Cypress\USB\Hardware\EZ-USB Series 2100\DEVBD REVD for the EZ-USB for the circuit diagram.
The load capacitors, C1 and C2, should be chosen so that the equation below is satisfied. CL is the load specified for the crystal. CL = ((C1 * C2)/(C1 + C2)) + CSTRAY
For C1 = C2 the equation is:
CL = 0.5*C + CSTRAY, where C = C1 = C2
Solving for C:
C = 2*(CL-CSTRAY) For CSTRAY = 5 pF and CL = 20 pF
The value for each of the two load capacitors is: C = 2*(20-5) = 30 pF
A more available value, but not out of range so that frequency will be affected is: C1 = C2 = 27 pF.
For typical crystals, C1 and C2 will be in the range of 20 to 33 pF.