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().

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.

(:source lang=arduino tabwidth=4:) int pin = 13;

(:sourceend:)

The Arduino Due board has powerful interrupt capabilities that allows you to attach, potentially, an interrupt function on all available pins. Thus, with the Due only, you can specify directly the pin number in attachInterrupt.

(:table border=0 cellpadding=5 cellspacing=0 width=80%:) (:cell width=400px:) attachInterrupt(interrupt, function, mode) (:cellnr width=400px:) attachInterrupt(pin, function, mode) (:cell:) (Arduino Due only) (:tableend:)

(:table border=0 cellpadding=5 cellspacing=0 width=80%:) (:cell width=150px:) interrupt: (:cell width=240px:) the number of the interrupt (int)

(:cellnr width=150px:) pin: (:cell width=240px:) the pin number (:cell:)(Arduino Due only)

(:cellnr width=150px:) function: (:cell width=240px:) 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.

(:cellnr width=150px:) mode: (:cell width=240px:) defines when the interrupt should be triggered. Four contstants are predefined as valid values:

(:cellnr width=150px:) (:cell width=240px:) The Due board allows also:

(:cellnr width=150px:) (:cell width=240px:)

• HIGH to trigger the interrupt whenever the pin is high.

(:cell:)(Arduino Due only)

(:tableend:)

The table below shows the available interrupt pins on various Arduino boards.

Specifies a function to call when an external interrupt occurs. Replaces any previous function that was attached to the interrupt. The Arduino Uno has two external interrupts: numbers 0 (on digital pin 2) and 1 (on digital pin 3).

The table below shows the available interrupt pins on the other Arduino boards.

Specifies a function to call when an external interrupt occurs. Replaces any previous function that was attached to the interrupt. The Arduino Uno has two external interrupts: numbers 0 (on digital pin 2) and 1 (on digital pin 3). The following table show the available interrupt pins on the other Arduino boards.

attachInterrupt()

Syntax

attachInterrupt(interrupt, function, mode)

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 Arduino Mega has an additional four: numbers 2 (pin 21), 3 (pin 20), 4 (pin 19), and 5 (pin 18).

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: 0 (on digital pin 2) and 1 (on digital pin 3). The Arduino Mega has an additional four: numbers 2 (pin 21), 3 (pin 20), 4 (pin 19), and 5 (pin 18).

interrupt: the number of the interrupt (int)

Specifies a function to call when external interrupt 0 or 1 occurs, on digital pin 2 or 3, respectively. Replaces any previous function that was attached to the interrupt.

interrupt: the number of the interrupt (int): 0 or 1.

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.

mode defines when the interrupt should be triggered. Four contstants are predefined as valid values:

Note

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.

Specifies a function to call when external interrupt 0 or 1 occurs, on digital pin 2 or 3, respectively.

Note: 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.

interrupt:: the number of the interrupt (int): 0 or 1.

If you wanted to insure that a program always caught the pulses from a rotary encoder, never missing 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 doorbell.

attchInterrupt enables interrupts 0 or 1, on digital pins 2 or 3 respectively. It also specifies the function to call when an external interrupt occurs.

If you wanted to insure that a program always caught the pulses from a rotary encoder, never missing 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 which it 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 doorbell.

Interrupts can be used with internal hardware too, such as timers, but as of Arduino 008, this requires AVR code and is not supported in the Arduino core.

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.

mode: defines when the interrupt should be triggered. Four contstants are predefined as valid values:

mode: when the interrupt should be triggered. Four contstants are predefined as valid values:

interrupt:: the number of the interrupt (int), with a valid value of 0 or 1.

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 the interrupt service routine.

Using Interrupts

Interrupts are useful for making things happen automatically in microcontroller programs, and can help solve timing problems. A good task for using an interrupt might be reading a rotary encoder, monitoring user input.

If you wanted to insure that a program always caught the pulses from a rotary encoder, never missing a pulse, it would make it very tricky to write a program to do anything else, because the program would need to constantly "listen" for the encoder, in order to catch pulses when they occured.

interrupt: the number of the interrupt (int), with a valid value of 0 or 1.

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 the interrupt service routine.

mode: when the interrupt should be triggered:

interrupt: the number of the interrupt (int), with a valid value of 0 or 1.

mode: when the interrupt should be triggered:

• LOW to trigger the interrupt whenever the pin is low,
• CHANGE to trigger the interrupt whenever the pin changes value
• RISING to trigger when the pin goes from low to high,
• FALLING for when the pin goes from high to low.

attchInterrupt enables interrupt 0 or 1, on digital pins 2 and 3 respectively. It also specifies the function to call when an external interrupt occurs.

You also should declare as volatile any variables that you modify within your interrupt handling function (see the example).''

Note: you may need to declare as volatile any variables that you modify within your interrupt handling function (see the example).

volatile int state = LOW;

  digitalWrite(pin, state);

Note: millis() and delay() won't work in your interrupt-handling function. Any serial data received while in your interrupt-handling function will be lost.

Note: millis() and delay() won't work in your interrupt-handling function. Any serial data received while in your interrupt-handling function will be lost.

[@int pin = 13;

[@ int pin = 13;

 
int pin = 13;
int state = LOW;

void setup()
{
  pinMode(pin, OUTPUT);
  attachInterrupt(0, blink, CHANGE);
}

void loop()
{
}

void blink()
{
  state = !state;
  digitalWrite(pin, state);
}

attachInterrupt(interrupt, function, mode)

Description

Specifies the function to call when an external interrupt occurs. There are two external interrupts (0 and 1), on digital pins 2 and 3 respectively.

Parameters

interrupt: the number of the interrupt (int)

function: the function to call when the interrupt occurs; this function must take no parameters and return nothing.

mode: when the interrupt should be triggered: LOW to trigger the interrupt whenever the pin is low, CHANGE to trigger the interrupt whenever the pin changes value, RISING to trigger when the pin goes from low to high, and FALLING for when the pin goes from high to low.

Returns

none

Example

See also

• detachInterrupt