//on the sender side
void setup() {
  Serial.begin(9600);//this has to match the serial speed you configured for the respective XBee
}
void loop() {
  Serial.write(20); //or the value you want to send
}

//on the receiver side
int received;
void setup() {
  Serial.begin(9600);//this has to match the serial speed you configured for the respective XBee
}
void loop() {
  if (Serial.available()) {
    received=Serial.read();
  }
}