Arduino mega 2560 interrupt pins2/29/2024 ![]() ![]() I also understand that further interrupts are disabled by default. I have used AVR development for a non-Arduino board, but prefer to have my students use the Arduino constructs where possible, and it is possible in this application (yes, I am an educator). I also understand how to use interrupts in AVR code directly. I have verified that the documented interrupt numbers and pins for Mega DO work with the Arduino attachInterrupt construct. ![]() My question is answered but I believe I should clarify for other readers. The Arduino Mega has an additional four: numbers 2 (pin 21), 3 (pin 20), 4 (pin 19), and 5 (pin 18). Most Arduino boards have two external interrupts: numbers 0 (on digital pin 2) and 1 (on digital pin 3). So stick to this from the arduino reference when wiring up interrupts: Also I don't think there is any implied 'priority' between the interrupts, it's just first come first service, and when inside a active interrupt service routine all other interrupts are disabled until the active ISR returns. There is no direct relationship from the AVR user interrupt pin names (INT0, etc) and the Arduino external interrupt numbers used with the AttachInterrupt function (numbers 0-5), you just have to live with the pin mapping the arduino uses. So am I correct in concluding that pin21 is the highest priority (INT0) even though it is neither the lowest nor highest interrupt number in Arduino land? My tests verify that the documented interrupt numbers and pin numbers work with attachInterrupt(), so this isn't a huge deal except that the Atmega interrupt priorities are determined by lowest INT number. Yet the schematic shows pin2 connected to INT4 and pin21 to INT0. The Mega 2560 documentation says, for example, that pin2 is interrupt 0, and pin21 interrupt is 2. This is both a software and hardware question - apologies if it doesn't belong here, but I didn't see a more appropriate forum area. ![]()
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