void setup() {
 pinMode(13,OUTPUT);
 pinMode(2,OUTPUT); 

}

void loop() {
digitalWrite(13,1);//active anode (anode fixed)
delay(3000);
digitalWrite(13,0);
delay(3000); 
digitalWrite(2,1);//active cathode(cathode fixed)
delay(3000);
digitalWrite(2,0);
delay(3000);
}