When the USART is transmitting a character and gets a NACK, it can automatically repeat the character before moving on to the next one. Repetition is enabled by writing US_MR.MAX_ITERATION to a value greater than 0. Each character can be transmitted up to eight times; the first transmission plus seven repetitions.
If MAX_ITERATION does not equal zero, the USART repeats the character as many times as the value loaded in MAX_ITERATION.
When the USART repetition number reaches MAX_ITERATION and the last repeated character is not acknowledged, the US_CSR.ITER is set. If the repetition of the character is acknowledged by the receiver, the repetitions are stopped and the iteration counter is cleared.
US_CSR.ITER can be cleared by writing a ‘1’ to US_CR.RSTIT.