B&B Electronics Celeron M Universal Network Controller with PC/104 Extension UNO-2170 - Manual (Page 17)

2.3.6 RS-485 Auto Flow Control Mode and RS-422 Master/Slave
Mode Selection
You can set the “Auto Flow Control mode of RS-485 or “Master/Slave＂ mode
of RS-422 by using the SW3 DIP switch for each RS-422/485 port. In RS-485,
if the switch is set to “Auto＂ the driver automatically senses the direction of
the data flow and switches the direction of transmission. No handshaking is
necessary.
In RS-422, if DIP switch is set to “On＂, the driver is always enabled, and
always in high or low status.
11 Chapter 2