Use DFRobot IO Expansion Shield with XBee PRO 900

I have searched the solution for a long time to use DFRobot IO Expansion Shield ( with XBee PRO 900. But there is no help. After reading the manual ( and Schematics ( carefully, I have successfully made UNO + IO Expansion Shield + XBee PRO 900 communicating with PC + X-CTU + XBee PRO 900. Here is the solution, hope it helps as an instruction.

  1. Make the 3 jumpers all connect to APC side (opposite to 485). This will use XBee PRO. It does not need additional wiring. The IO Expansion Shield has connect APC-TXD to pin 0(RX), APC-RXD to pin 1(TX), DTR(EN) to pin 2.
  2. Upload the sketch to UNO. Make sure the XBee PRO is not connected otherwise uploading will fail for serial port occupied by XBee PRO.
  3. Plug IO Expansion Shield with XBee PRO into UNO.
  4. To receive data, write LOW to EN.
  5. To transmit data, write HIGH to EN.

Here is my codes (UNO).

int buzzerPin = 8;
int EN = 2;
int val;

void setup() 
  pinMode(buzzerPin, OUTPUT);
  pinMode(EN, OUTPUT);

void loop()
  digitalWrite(EN, LOW); //Enable Receiving Data
  val =;
  if (-1 != val) {
    if ('A' == val) {
      tone(buzzerPin, 2500, 200);
      digitalWrite(EN, HIGH); //Enable Transmitting Data
      Serial.println("XBee PRO 900 received");

To use DFRobot IO Expansion shield with Xbee, all you need to do is the set the jumpers to Serial. And nothing else you need to do.

The rest bit is just to send and receive data as standard serial port.