Advantech UNO-1170E - Manual (Page 20)

UNO-1170 User Manual 12
2.3.5 Terminal Resistor Setup for RS-422/485
The onboard termination resistor (120 Ohm) for COM2/COM3 can be
used for long distance transmission or device matching. (Default Open.)
Each terminal resistor responds to different channels for RS-422/485.
Usually, these resistors are needed for both ends of the communication
wires and the value of the resistors should match the characteristic imped-
ance of the wires used.
2.3.6 RS-485 Auto Flow & RS-422 Master/Slave Mode
You can set the “Auto Flow Control” mode of RS-485 or “Master/Slave”
mode of RS-422 by using the SW2 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.
Table 2.3: Terminal Resistor Settings
COM port Switch No. Pin Setting Description
COM3 SW3 1 ON 120 Ohm between Data+/
Data- (RS-485)
Or 120 Ohm between Tx+/Tx-
(RS-422)
OFF Open (Default)
2 ON 120 Ohm between Rx+/Rx-
(RS-422)
OFF Open (Default)