TXD Pin Override Not Released When Disabling the Transmitter

The USART will not release the TXD pin override if:
  • The USART transmitter is disabled by writing the TXEN bit in USART.CTRLB to ‘0’ while the USART receiver is disabled (RXEN in USART.CTRLB is ‘0’)
  • Both the USART transmitter and receiver are disabled at the same time by writing the TXEN and RXEN bits in USART.CTRLB to ‘0

Work Around

There are two possible work arounds:
  • Make sure the receiver is enabled (RXEN in USART.CTRLB is ‘1’) while disabling the transmitter (writing TXEN in USART.CTRLB to ‘0’)
  • Writing to any register in the USART after disabling the transmitter will start the USART for long enough to release the pin override of the TXD pin

Affected Silicon Revisions

Rev. A