The DSWDT provides another wake-up source for Deep Sleep. It is a separate module specific to Deep Sleep that requires a clock source to keep track of how long to stay in Deep Sleep. Two options are available: an internal low-power RC oscillator or an external secondary oscillator. The DSWDT should always be run from the internal RC oscillator if robustness is needed, allowing an application to wake up even if a crystal failure has occurred. Configuration bits specify how long the device should stay in Deep Sleep before timing out and waking the device. Sixteen different timeout settings are available. If more granularity is needed, a RTCC alarm should be used instead.