void setup()
{
  Serial3.begin(19200, SERIAL_8N2);
  Serial.begin(19200, SERIAL_8E1);
  delay(1000);
}

void generalpol()
{
  delay(200);
  Serial3.write(0x80);
  //Serial3.write(0x81);
}

void loop()
{
  generalpol();
  if(Serial3.available()){
    int j = Serial3.available();
    char commandbuffer[j];
    for (int i =0 ; i<j ; i++)
    {
      while( Serial3.available()) {
        commandbuffer[i] = Serial3.read();
        delay(1000);
      }
    }
  }
}