13
Chapter 2
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
Setting
Description
COM1
SW4
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)
COM2
SW5
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)
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