The pins used for interfacing the USART may be multiplexed with the PIO lines. The programmer must first program the PIO controller to assign the desired USART pins to their peripheral function. If I/O lines of the USART are not used by the application, they can be used for other purposes by the PIO Controller.
All the pins of the modems may or may not be implemented on the USART. On USARTs not equipped with the corresponding pin, the associated control bits and statuses have no effect on the behavior of the USART.