19.6.2.3 External Wake-Up Detector

The External Wake-up detector is activated in Backup Sleep Mode only. In all other sleep modes, the debounce counter is stopped. Before entering Backup Mode, each external wake-up pin can be enabled by configuring the Wake-up Enable (WKEN) register. The corresponding I/O lines must also be configured in input mode using port configuration (PORT). The wake-up level can also be configured by using the Wake-up Polarity (WKPOL) register. If WKPOLx is written to 0 (default value), the input wake-up pin is active low. If WKPOLx=1 the pin is active high. All the resulting signals are wired-ORed to trigger a debounce counter which can be programmed with the Wake-up Debounce Configuration (WKDBCONF) register.

In Backup Mode, the debounce counter is running if at least one external wake-up pin is enabled and the WKDBCONF is configured to any other value than OFF. It is clocked by the OSCULP32K clock provided by the OSC32KCTRL module. If an enabled wake-up pin is asserted for a time longer than the debouncing period, the BKUPEXIT.EXTWAKE bit is set, and the value of each enable external wake-up pin is stored in the WKCAUSE register. This will allow the application to identify the external wake-up source when booting up from a backup exit reset. A backup reset is then applied. Refer to Reset Causes and Effects for details.