Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 18)

18 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 1 Isolated Analog I/O Module Operation in the ControlLogix System
Listen-only Mode Any controller in the system can listen to the data from any I/O module, that is,
input data or ‘echoed’ output data, even if the controller does not own
the module.
During the I/O configuration process, you can specify a ‘Listen-Only’
connection. For more information on Connection options when configuring
your system, see
page 125 .
When you choose a ‘Listen-Only’ connection, the controller and module
establish communication without the controller sending configuration data. In
this instance, another controller owns the I/O module.
IMPORTANT If any controller uses a ‘Listen-Only’ connection to the module, none of the
other connections over the EtherNet/IP network can use the Unicast option.
The ‘Listen-Only’ controller receives multicast data from the I/O module as
long as a connection between a controller and I/O module is maintained
If the connection between all owner-controllers and the module is broken,
the module stops multicasting data and connections to all ‘Listening
controllers’ are also broken.