Listen-only mode – Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules User Manual
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Publication 1756-UM009C-EN-P - December 2010
Chapter 2
Analog 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 (that
is, input data or ‘echoed’ output data) even if the controller does not own the
module. In other words, the controller does not have to own a module’s
configuration data to listen to it.
During the I/O configuration process, you can specify one of several
‘Listen-Only’ modes in the Comm Format box on the New Module dialog
box. See
for more Comm Format details.
Choosing a ‘Listen-Only’ mode option allows the controller and module to
establish communications without the controller sending any configuration
data. In this instance, another controller owns the module being listened to.
IMPORTANT
If a ‘Listen-Only’ connection is being used by any controller to
the module, any connections over the Ethernet network cannot
use the Unicast option. See the Unicast box on
for details.
The ‘Listen-Only’ controller continues to receive multicast data
from the I/O module as long as a connection between an
owner-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.