34 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 2 Digital I/O Operation in the ControlLogix System
Listen-only Mode
Any controller in the system can listen to the data from any I/O module, such as
input data, echoed output data, or echoed diagnostic information. Even if a
controller does not own a module, or hold the module’s configuration data, the
controller can still listen to the module.
During the module configuration process, you can specify one of several Listen
modes. For more information, see Communication or Connection Formats
on
page 131.
Choosing a Listen mode allows the controller and module to establish
communication without the controller sending any configuration data. In this
instance, another controller owns the module being listened to.
Multiple Owner-Controllers
of Input Modules
If a connection is lost between an owner-controller and a module, the connection
is also lost between any controllers listening to that module. As a result, the
ControlLogix system lets you define more than one owner-controller for input
modules.
In the illustration below, controller A and controller B both have been configured
to be owner-controllers of the same input module.
Figure 6 - Identical Owner-Controller Configurations for Input Module
In Listen-only mode, controllers continue to receive data multicast from the I/O
module as long as the connection between the owner-controller and I/O
module is maintained.
If the connection between the owner-controller and module is broken, the
module stops multicasting data and connections to all listening controllers are
also broken.
Only input modules can have multiple owner-controllers. If multiple owner-
controllers are connected to the same input module, they must maintain
identical configurations for that module.
Input Module
Configuration
Data
Xxxxx
Xxxxx
Xxxxx
Input Module
Configuration
Data
Xxxxx
Xxxxx
Xxxxx
41056
Initial Configuration Initial Configuration
A
B
Input
A B
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