25.11.1.1 Software Generated Shutdown
Setting the SHUTDOWN bit will force the CWG into the Shutdown state.
When the auto-restart is disabled, the Shutdown state will persist as long as the SHUTDOWN bit is set.
When auto-restart is enabled, the SHUTDOWN bit will clear automatically and resume operation on the next rising edge event. The SHUTDOWN bit indicates when a Shutdown condition exists. The bit may be set or cleared in software or by hardware.