External interrupts in Arduino & its limitations

Description

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).

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. 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:

• 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.

Returns

none

Example

int pin = 13;
volatile int state = LOW;

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

void loop()
{
  digitalWrite(pin, state);
}

void blink()
{
  state = !state;

}