#define NEXT_INC_SIZE 2

void sendAck(){
  char outData[2];
  outData[0] = 0xBB;
  outData[1] = 0xCC;
  Serial.write(outData, 2); //Write the ack data
}

void setup() {

  Serial.begin(19200);
  Serial.println("Started");
}

void loop() {

  if(Serial.available() >= NEXT_INC_SIZE) {

    char incomingBytes[2];
    Serial.readBytes(incomingBytes, NEXT_INC_SIZE);

    Serial.println(incomingBytes);
    sendAck();
  }
}