Arduino LED Blink

void setup() {
  pinMode(LED_BUILTIN, OUTPUT); // LED_BUILTIN = 13 for Arduino ATMEGA 256
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   
  delay(500);                       
  digitalWrite(LED_BUILTIN, LOW);    
  delay(1000);                      
}