void setup() {
  pinMode(8, INPUT_PULLUP);
  pinMode(8, INPUT_PULLUP); 
  pinMode(13, OUTPUT); 
  pinMode(13, OUTPUT);       
  // digitalWrite(13, LOW);    

  Serial.begin(9600);      
}

void loop() {
  if (Serial.available()) {
    char data_rcvd = Serial.read();   

    if (data_rcvd == '1') digitalWrite(13, HIGH); 
    if (data_rcvd == '0') digitalWrite(13, LOW);  
  }

  if (digitalRead(8) == HIGH) {
    Serial.write('0');  
    digitalWrite(13, LOW);
  } else {
    Serial.write('1');   
    digitalWrite(13, HIGH);
  }
  if (Serial.available()) {
    char data_rcvd = Serial.read();   

    if (data_rcvd == '1') digitalWrite(13, HIGH); 
    if (data_rcvd == '0') digitalWrite(13, LOW);  
  }

  if (digitalRead(8) == HIGH) {
    Serial.write('0');  
    digitalWrite(13, LOW);
  } else {
    Serial.write('1');   
    digitalWrite(13, HIGH);
  }
}