Terminal Resistor Setup For Rs-422/485 - Advantech UNO-3072A User Manual

2.2.5 Terminal Resistor Setup for RS-422/485

The onboard termination resistor (120 Ohm) for COM1/COM2 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.
Table 2.1: Terminal Resistor Settings
COM Port Switch No. Pin
COM1 SW4
COM2 SW5
Setting
1 ON
OFF
2 ON
OFF
1 ON
OFF
2 ON
OFF
13
Description
120 Ohm between Data+/
Data- (RS-485)
Or 120 Ohm between Tx+/Tx-
(RS-422)
Open (Default)
120 Ohm between Rx+/Rx-
(RS-422)
Open (Default)
120 Ohm between Data+/
Data- (RS-485)
Or 120 Ohm between Tx+/Tx-
(RS-422)
Open (Default)
120 Ohm between Rx+/Rx-
(RS-422)
Open (Default)
Chapter 2