Manual

32 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
page 205 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
page 209
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.