Secondary Oscillator Initialization

The SOSC is a separate oscillator block in the device that is required in order to use the ACT module. The oscillator block is optimized for a 32.768 kHz crystal oscillator connected to the SOSCI and SOSCO pins. There are two register bits associated with SOSC configuration: the Secondary Oscillator Power Mode Selection (SOSCPWR) bit of OSCCON3, and the Secondary Oscillator Manual Request (SOSCEN) bit of OSCEN.

In the event of a Power-on-Reset (POR) event, SOSCPWR is cleared and will operate in Low-Power mode. The SOSCEN bit is also cleared, leaving the SOSC in a state where it could be enabled by another peripheral. These settings allow the ACT module to enable the SOSC.

In low-power applications (e.g., battery-powered devices), the low-power setting of SOSCPWR is appropriate. The High-Power mode may be necessary for crystals requiring higher drive strength. To enable High-Power mode the SOSCPWR bit of the OSCCON3 must be set.