32.6.3.6 RS485

RS485 is available with the following configuration:
  • USART frame format (CTRLA.FORM = 0x00 or 0x01)
  • RS485 pinout (CTRLA.TXPO = 0x3)
The RS485 feature enables control of an external line driver as illustrated in the following figure. While operating in RS485 mode, the transmit enable pin (TE) is driven high when the transmitter is active.
Figure 32-15. RS485 Bus Connection

The TE pin remains high for the complete frame including the stop bit(s). If a Guard Time is programmed in the Control C register (CTRLC.GTIME), the line remains driven after the last character completion. The following figure illustrates a transfer with one stop bit and CTRLC.GTIME = 3.

Figure 32-16. Example of TE Drive with Guard Time

The Transmit Complete interrupt flag (INTFLAG.TXC) is raised after the guard time is complete and TE goes low.