We are using MKL17Z controller (CM0+ core) in our project. The PORTA pin 13 is configured as digital input with negative edge interrupt. The interrupt is generated on falling edge by an external square wave of 60Hz applied to the pin 13. After entering the ISR the PORTA_ISFR bit 13 is SET immediately so as to clear the interrupt flag. I checked the ISR operation by toggling a pin. The ISR works fine for most of the time but sporadically the control enters the ISR even on positive edge. This is somthing strange! I have ensured that the interrupt configuration is not changed in the code at any time. Has anybody faced such problem?