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13 Chapter 2

2.4 Terminal Resistor Setup for RS-422/485

The onboard termination resistor (120 Ohm) for COM1-6, COM A,

and COM B can be used for long distance transmission or device match-

ing (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.

Terminal Resistor Settings

COM Port Switch Pin Setting Description

COM 1,2 SW 11 1 (COM1) ON 120 Ohm between Data+/

Data-

OFF Open (Default)

2 (COM2) ON 120 Ohm between Data+/

Data-

OFF Open (Default)

COM A

COM B

SW 10

SW 9

1 ON 120 Ohm between Data+/

Data- (RS-485 COM A, B

only)

Or 120 Ohm between Tx+/

Tx-

(RS-422)

OFF Open (Default)

2 ON 120 Ohm between Rx+/Rx-

(RS-422)

OFF Open (Default)

COM 3

COM 4

COM 5

COM 6

SW 6 1 (COM3) ON 120 Ohm between Data+/

Data-

2 (COM4)

3 (COM5) OFF Open (Default)

4 (COM6)

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Advantech UNO-2178A Manual de usuario Pagina 21