void setup(){
  pinMode(PA0,OUTPUT);
  pinMode(PA1,OUTPUT);
  pinMode(PA2,OUTPUT);
  pinMode(PA3,OUTPUT);
}
void loop(){
  digitalWrite(PA0,HIGH);
  digitalWrite(PA1,LOW);
  digitalWrite(PA2,LOW);
  digitalWrite(PA3,LOW);
  delay(1000);
  digitalWrite(PA0,HIGH);
  digitalWrite(PA1,HIGH);
  digitalWrite(PA2,LOW);
  digitalWrite(PA3,LOW);
  delay(1000);
  digitalWrite(PA0,LOW);
  digitalWrite(PA1,HIGH);
  digitalWrite(PA2,LOW);
  digitalWrite(PA3,LOW);
  delay(1000);
  digitalWrite(PA0,LOW);
  digitalWrite(PA1,HIGH);
  digitalWrite(PA2,HIGH);
  digitalWrite(PA3,LOW);
  delay(1000);
  digitalWrite(PA0,LOW);
  digitalWrite(PA1,LOW);
  digitalWrite(PA2,HIGH);
  digitalWrite(PA3,LOW);
  delay(1000);
  digitalWrite(PA0,LOW);
  digitalWrite(PA1,LOW);
  digitalWrite(PA2,HIGH);
  digitalWrite(PA3,HIGH);
  delay(1000);
  digitalWrite(PA0,LOW);
  digitalWrite(PA1,LOW);
  digitalWrite(PA2,LOW);
  digitalWrite(PA3,HIGH);
  delay(1000);
}