32.5.1 I/O Lines

Using the USART’s I/O lines requires the I/O pins to be configured using the I/O Pin Controller (PORT).

When the SERCOM is used in USART mode, the SERCOM controls the direction and value of the I/O pins according to the table below. The PORT Control bit PINCFGn.DRVSTR is still effective for the SERCOM output pins. The PORT Control bit PINCFGn.PULLEN is still effective on the SERCOM input pins, but is limited to the enabling or disabling of a pull down only (it is not possible to enable or disable a pull up). If the receiver or transmitter is disabled, these pins can be used for other purposes.

Table 32-2. USART Pin Configuration
PinPin Configuration
TxDOutput
RxDInput
XCKOutput or input

The combined configuration of PORT and the Transmit Data Pinout and Receive Data Pinout bit fields in the Control A register (CTRLA.TXPO and CTRLA.RXPO, respectively) will define the physical position of the USART signals in the previous table USART Pin Configuration.

References:

PORT - I/O Pin Controller