Rockwell Automation 999 IMC S Class Compact Motion Controller (Cat. No. 4100-999-122) - Manual (Page 50)

4-8 Installation and Hookup
Publication 999-122 - January 1997
Configure the Serial Ports
Serial port A may be independently configured for RS-232 or RS-422
operation and serial port B may be independently configured for
RS-232C, RS-422, or DH-485 operation via switch SW1 on the motion
controller module inside the IMC-S/23x. If RS-422 or DH-485 is
selected, the port may also be configured to use or not use a termination
resistor.
The serial port configuration switch layout is shown below. In
IMC-S/23x-RL models, the switches are between the AxisLink and
RIO boards (on the main board).
The leftmost switch selects RS-232 (down) or RS-422 (up)
communications for serial port A. If RS-422 communications are
selected, the next switch to the right determines whether the port is
terminated (up) or not (down) with a 220 W resistor. If RS-232
communications are selected, the port should not be terminated (second
switch down). The next pair of switches provide the same selections
for serial port B. The rightmost pair of switches determines whether
port B is used for RS-232/RS-422 communication (down) or DH-485
communication (up) and whether the DH-485 port is terminated (up)
or not (down) with a 220 W resistor. As shipped from the factory, both
ports are configured for RS-232C operation, as shown in the figure
above.