Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 25
Digital I/O Operation in the ControlLogix System Chapter 2
The input, or data echo, information is limited to general faults and data. No
additional status, such as diagnostic information, is available.
The illustration below shows how a rack-optimized connection eliminates the
need for three separate connections. The owner-controller in the local chassis
communicates with all the I/O modules in the remote chassis but uses only one
connection. The ControlNet communication module sends data from the
modules simultaneously at the RPI.
Figure 2 - Rack-optimized Connection
Because rack-optimized connections are applicable only in applications that
use a remote chassis, you must configure the communication format , as
described in Chapter 7
, for both the remote I/O module and the remote
1756-CNB module or EtherNet/IP module.
Make sure you configure both modules for rack optimization. If you choose a
different communication format for each module, the controller makes two
connections to the same chassis (one for each format) and the same data
travels across the ControlNet network.
If you use rack optimization for both modules, you preserve bandwidth and
configure your system to operate more efficiently.
Each controller can establish connections, in any combination of direct or rack-
optimized. In other words, you can use a rack-optimized connection between
an owner-controller and multiple remote I/O modules while simultaneously
using a direct connection between that same controller and any other I/O
modules in the same remote chassis.
Local Chassis
Remote Chassis
ControlNet Network
41021
One Connection for
All Remote I/O
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