void setup() {
  // put your setup code here, to run once:
  pinMode(9, OUTPUT);
  pinMode(8, OUTPUT);
}

void loop() 
{
  // put your main code here, to run repeatedly:
  digitalWrite(9, HIGH);  digitalWrite(8, LOW);
  delay(500);
  digitalWrite(8, HIGH);  digitalWrite(9, LOW);
  delay(500);
}