void setup()
{
  Serial.begin(9600);
  pinMode(13, OUTPUT); 
  attachInterrupt(0, ExternalInterrupt, RISING);
}

void loop()
{
  digitalWrite(13, HIGH);   // set the LED on
  delay(1000);              // wait for a second
  digitalWrite(13, LOW);    // set the LED off
  delay(1000);              // wait for a second

}

void ExternalInterrupt()
{
  Serial.println("Interrupt!!!");
}