Hi @PapiAli. The port is 2 way! I have several projects with separate data-streams going Processing->Ard and Ard->Processing. There are many reasons why it might not appear to be working. Most Ard have leds TX and RX (Transmit and receive.) Simply seeing the RX light flashing proves that Processing is sending something. It doesn’t prove the Ard understands it in the way you want. I suggest you try each of the Serial examples (Processing, File, Examples, Libraries, Serial). While you are developing transmit only 2/Sec so you can see the lights flash and the prints of what you are transmitting.