SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442
The UART_MDR3[4] DIR_EN bit enables hardware control over an external transceiver to support RS-485. The direction signal comes across the DIR port. The direction polarity is controlled by the UART_MDR3[3] DIR_POL bit. The direction is determined by the hardware monitoring the TX FIFO and the TX shift register. When both are empty the transceiver is set to RX. There is a guard band delay counter of 3 bit clock cycles after the TX shift register is going empty to allow time for the stop bit to transition through the transceiver before a direction change to receive might be applied.
Figure 12-271 shows the direction control.