User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 102
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9.3.9 EM4 Wakeup Reset
Whenever the system is woken up from EM4 on a pin wake-up request, the EM4WURST bit is set. This
bit enables the user to identify that the device was woken up from EM4 using a pin wake-up request.
Upon wake-up this bit should be cleared by software.