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. PORT Control bit PINCFGn.DRVSTR is still effective for the SERCOM output pins. PORT Control bit PINCFGn.PULLEN is still effective on the SERCOM input pins, but is limited to the enabling/disabling of a pull down only (it is not possible to enable/disable a pull up). If the receiver or transmitter is disabled, these pins can be used for other purposes.

Table 1. USART Pin Configuration
Pin Pin Configuration
TxD Output
RxD Input
XCK Output 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 table above.