27.4 Secondary Oscillator

A secondary low-power 32.768 kHz oscillator circuit is built-in between pins SOSCI (input) and SOSCO (amplifier output). This internal circuit is to be used in conjunction with an external 32.768 kHz crystal. The secondary oscillator is not dedicated only to Timer1; it can also be used by other modules.

The oscillator circuit is enabled by setting the SOSCEN bit of the OSCEN register. This can be used as one of the Timer1 clock sources selected with the CS bits. The oscillator will continue to run during Sleep.

Important: The oscillator requires a start-up and stabilization time before use. Thus, the SOSCEN bit of the OSCEN register must be set and a suitable delay observed prior to enabling Timer1. A software check can be performed to confirm if the secondary oscillator is enabled and ready to use. This is done by polling the secondary oscillator ready Status bit. Refer to the “OSC - Oscillator Module (with Fail-Safe Clock Monitor)” chapter for more details.