4.2.1 External Clock Sources

An external clock source can be used as the device system clock by performing one of the following actions:

• Program the RSTOSC<2:0> and FEXTOSC<2:0> bits in the Configuration Words to select an external clock source that will be used as the default system clock upon a device Reset.
• Write the NOSC<2:0> and NDIV<3:0> bits to switch the system clock source.