Trouble Reattching Interrupt

[system]

Gammon Forum : Electronics : Microprocessors : Interrupts

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Something to be aware of is that these flags can be set before you attach the interrupt handler. For example, it is possible for a rising or falling level interrupt on pin D2 to be "flagged", and then as soon as you do an attachInterrupt the interrupt immediately fires, even if the event occurred an hour ago. To avoid this you can manually clear the flag. For example:

EIFR = _BV (INTF0);  // clear flag for interrupt 0

EIFR = _BV (INTF1);  // clear flag for interrupt 1

That did the trick. Clearing the flags before attaching and reattaching makes the program run exactly as intended. Thank you for sharing your superb resource as well, I'll be sure to come back and read more.