Guard Time

To ensure enough turn-around time for line drivers when operating in RS485 mode, the USART has a built-in guard time mechanism to relax the timing when changing direction from RX to TX mode. The guard time is represented by the idle bits inserted before the next start bit of the first response byte is transmitted. The number of idle bits can be configured through the Guard (GUARD) bit field in the Control F (USARTn.CTRLF) register. The duration of each idle bit is given by the baud rate used by the current transmission.