Rockwell Automation 1770 DH,DHII,DH485 CABLE - Manual (Page 73)

DH II Overview
Chapter 4
4-2
Figure 4.1 shows an example of a DH II network.
Figure 4.1
A typical DH II cable system.
PLC - 2 PLC - 3
To Data Highway Plus
1779-KP5/KP5R*
1779-KFL/KFLR*
1779-KMF/KMFR*
Computer Robot IBM-PC
Data Highway II
1779-KP2/KP2R* 1779-KP3/KP3R*
* An "R" in the product name denotes a redundant module. 18770
You can also order your DH II interface modules with a redundant-cabling
option. To use redundant cabling, you must choose this option for all the
interface modules on your network.
Redundant cabling modules allow you to run a second trunkline cable between
your modules. DH II redundant interface modules send signals down both
cables. The receiving module determines which of the two signals is a better
signal. By comparing the quality of the signals on each cable, the module can
use the best signal possible. There will also be a backup cable should one cable
fail.