24.3.2.6 RS-485 Mode of Operation

The RS-485 feature enables the support of external components to comply with the RS-485 standard.

Either an external line driver is supported as shown in the figure below (RS485=0x1 in USARTn.CTRLA), or control of the transmitter driving the TxD pin is provided (RS485=0x2).

While operating in RS-485 mode, the Transmit Direction pin (XDIR) is driven high when the transmitter is active.

Figure 24-10. RS-485 Bus Connection

The XDIR pin goes high one baud clock cycle in advance of data being shifted out, to allow some guard time to enable the external line driver. The XDIR pin will remain high for the complete frame including Stop bit(s).

Figure 24-11. XDIR Drive Timing