25.3.2.3.1 Disabling the Transmitter
When disabling the transmitter, the operation will not become effective until ongoing and pending transmissions are completed. That is, when the transmit shift register, Transmit Data (USARTn.TXDATAL and USARTn.TXDATAH) registers, and TX Buffer register do not contain data to be transmitted. When the transmitter is disabled, it will no longer override the TXD pin, and the PORT module regains control of the pin. The pin is automatically configured as an input by hardware regardless of its previous setting. The pin can now be used as a normal I/O pin with no port override from the USART.