17.6.4 32.768 kHz Ultra Low-Power Internal Oscillator (OSCULP32K) Operation
The OSCULP32K provides a tunable, low-speed, and ultra low-power clock source.
Note: The OSCULP32K is factory calibrated under typical voltage and temperature
conditions.
The OSCULP32K is enabled by default after a Power-on Reset (POR) and will always run except during POR.
Users can lock the OSCULP32K configuration by setting the Write Lock bit in the 32 kHz Ultra Low-Power Internal Oscillator Control register (OSCULP32K.WRTLOCK = 1). If set, the OSCULP32K configuration is locked until POR is detected.
The OSCULP32K can be used as a source for Generic Clock Generators (GCLK) or for the Real-Time Counter (RTC). To ensure proper operation, the GCLK or RTC modules must be disabled before the clock selection is changed.