Notice that only one of PAx-PGx, where x is one of 1-15, can be configured for as an EXTI source at any moment. In the event that multiple EXTI sources share a handler, pending interrupts can be determined from reading the pending register EXTI_PR. Also, any EXTI source can be “triggered” through software by setting the appropriate bit in the “software interrupt event register” EXTI_SWIER