void setup() {
  Serial.begin(9600);
  Serial1.begin(9600); 
  Serial2.begin(9600);
  pinMode(20, OUTPUT); //DE1
  pinMode(21, OUTPUT); //DE2


  digitalWrite(20, HIGH);
  Serial1.print('U'); //0x55
  delay(50);
  digitalWrite(20, LOW);
  while (Serial2.available()) {
    Serial.print((char)Serial2.read());
  }
}

void loop() {

}