63.5.2 Power Management
The peripheral clock is not continuously provided to the FLEXCOM. The programmer must first enable the FLEXCOM Clock in the Power Management Controller (PMC) before using the USART or SPI or TWI.
To enable asynchronous partial wakeup for the FLEXCOM, the PMC must be configured first. The FLEXCOM peripheral clock can be automatically provided depending on the instructions (requests) provided by the FLEXCOM to the PMC.