35.2.1.3 Transmit Data Polarity
The polarity of the transmit data is controlled with the TXPOL bit. The default
      state of this bit is ‘
0’, which selects high true transmit Idle and data
      bits. Setting the TXPOL bit to ‘1’ will invert the transmit data, resulting
      in low true Idle and data bits. The TXPOL bit controls transmit data polarity in all
      modes.