Arduino MEGA 2560 with the RS232 Shield

Hello,

I am a total beginner for Arduino. I am trying to connect the RS232 Shield to my Arduino MEga and send and receive messages to/from device that is connected to the DB9 of the shield. As soon as i connect the shield i lose the Serial interface of my Arduino. Is there any possibility to have that?

I read in docs here https://wiki.dfrobot.com/RS232_Shield that i have to switch off shield and then program board and then switch it on. How can i debug what is happening?

What is the simplest code i can use to send something to device and receive the response?

When i do for example this:

  uint8_t i, buffer[2];

  buffer[0] = '$';

  buffer[1] = '?';

  for (i = 0; i < sizeof(buffer); i++)

  {

    Serial.write(buffer[i]);

  }

  Serial.write('\n');

I can see the TXD LED blink on the shield and I also see in the Serial written '$?' 

But when i do Serial.printl I see nothing in the serial and RXD LED blinks on shield

Thank you