Hi season90, TX should be on digital pin 0 (PA22), as that's on SERCOM3/PAD[0]. Likewise, RX should be on digital pin 1 (PA23): Uart Serial_plc(&sercom3, 1, 0, SERCOM_RX_PAD_1, UART_TX_PAD_0); I'd also suggest calling the pinPeripheral() functions before testing the Serial_plc in the while() loo…