MVI69E-MBS ♦ CompactLogix Platform Reference
Modbus Serial Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 149 of 154
June 28, 2017
7.6.2 RS-422 Wiring
The RS-422 interface requires a single four or five wire cable. The Common
connection is optional, depending on the RS-422 network devices used. The
cable required for this interface is shown below:
7.6.3 RS-485 Wiring
The RS-485 interface requires a single two or three wire cable. The Common
connection is optional, depending on the RS-485 network devices used. The
cable required for this interface is shown below:
Note: Terminating resistors are generally not required on the RS-485 network, unless you are
experiencing communication problems that can be attributed to signal echoes or reflections. In
these cases, installing a 120-ohm terminating resistor between pins 1 and 8 on the module
connector end of the RS-485 line may improve communication quality.
RS-485 and RS-422 Tip
If communication in the RS-422 or RS-485 mode does not work at first, despite
all attempts, try switching termination polarities. Some manufacturers interpret +
and -, or A and B, polarities differently.
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