void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  Serial.write(0xAA);
}

void loop()
{
  int inByte;
  int outByte = 64 | 5;
  while (1) {
    if (Serial.available() > 0) {
      // get incoming byte:
      inByte = Serial.read();
      if (inByte == 0xFF) {
        Serial.write(outByte);
      }
      else {
         Serial.write('b'); 
      }
    }
  }
}