ProSoft Technology MVI56E-MCMR - Manual (Page 175)

MVI56E-MCMR ♦ ControlLogix Platform Reference
Modbus Communication Module with Reduced Data Block User Manual
ProSoft Technology, Inc. Page 175 of 225
May 13, 2014
6.4.5 RS-422
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:
6.4.6 RS-485 Application Port(s)
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.