The clock source of the reference clock peripheral is selected with the CLK bits. The available clock sources are listed in the following table:
| CLK | Clock Source |
|---|---|
| 111-101 | Unimplemented |
| 100 | SOSC |
| 011 | MFINTOSC (500 kHz) |
| 010 | LFINTOSC (31 kHz) |
| 001 | HFINTOSC |
| 000 | FOSC |