Specifies a function to call when an external interrupt occurs. Replaces any previous function that was attached to the interrupt. Most Arduino boards have two external interrupts: numbers 0 (on digital pin 2) and 1 (on digital pin 3). The table below shows the available interrupt pins on various boards.
The Arduino Due board has powerful interrupt capabilities that allows you to attach an interrupt function on all available pins. You can directly specify the pin number in attachInterrupt().
|attachInterrupt(interrupt, function, mode)|
|attachInterrupt(pin, function, mode)||(Arduino Due only)|
|interrupt:||the number of the interrupt (int)|
|pin:||the pin number||(Arduino Due only)|
|function:||the function to call when the interrupt occurs; this function must take no parameters and return nothing. This function is sometimes referred to as an interrupt service routine.|
defines when the interrupt should be triggered. Four contstants are predefined as valid values:
The Due board allows also:
||(Arduino Due only)|
Inside the attached function, delay() won't work and the value returned by millis() will not increment. Serial data received while in the function may be lost. You should declare as volatile any variables that you modify within the attached function.
Interrupts are useful for making things happen automatically in microcontroller programs, and can help solve timing problems. Good tasks for using an interrupt may include reading a rotary encoder, or monitoring user input.
If you wanted to insure that a program always caught the pulses from a rotary encoder, so that it never misses a pulse, it would make it very tricky to write a program to do anything else, because the program would need to constantly poll the sensor lines for the encoder, in order to catch pulses when they occurred. Other sensors have a similar interface dynamic too, such as trying to read a sound sensor that is trying to catch a click, or an infrared slot sensor (photo-interrupter) trying to catch a coin drop. In all of these situations, using an interrupt can free the microcontroller to get some other work done while not missing the input.
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The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.