#define LED 2                 // define LED port pin

void setup() {
  pinMode(LED, OUTPUT);       // configure port pin as output
}

void loop() {
  digitalWrite(LED, HIGH);    // set port pin at logic HIGH (turn the LED on)
  delay(500);                 // wait for 500 ms
  digitalWrite(LED, LOW);     // set port pin at logic LOW (turn the LED off)
  delay(500);                 // wait for 500 ms
}