Rockwell Automation 999 IMC S Class Compact Motion Controller (Cat. No. 4100-999-122) - Manual (Page 79)

Installation and Hookup 4-37
Publication 999-122 - January 1997
When DH-485 is used, serial port B on the motion controller is used
for DH-485 communication and the normal built-in operator interface
functions of the IMC S Class are unavailable. When DH-485 is used,
do not make any connections to serial port B on the motion controller.
!
ATTENTION: Do not connect anything to Serial
Port B of the IMC-S/23x if you are using DH-485
communications.