Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 36)

Using the Serial Ports
Chapter 4
4–12
Figure 4.9
Point-to-Point RS-422 Connections
Figure 4.10
Multi-drop configuration with master and multiple slaves
Important: When you use the peripheral port as a 422 port, you must
connect pin 4 to pin 5 on the port.
When using an RS-422 interface you must install termination resistors at
each end of the line. The module has a jumper selectable termination
resistor (Refer to figure 3.2). Use a cable with 2 twisted pairs and a
nominal impedance of 100 ohms.
Important: Use terminating resistors only at the ends of the link if using
multiple RS-422 devices, and at both ends if using point-to-point
connections.
4.4.5
Connecting RS-422 Devices
(continued)