Chapter 3: Operation Within the ControlLogix System
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Owner’s Guide 0300199-01 Rev. D
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.
NOTE
IMPORTANT
: Controllers using the Listen-Only mode continue to
receive data multicast from the I/O module as long as a connection
between an owner and I/O module is maintained. If the connection
between all owners and the module is broken, the module stops
multicasting data and connections to all ‘Listening controllers’ are also
broken.
Because ‘Listening controllers’ lose their connections to modules when
communications with the owner stop, the ControlLogix system will allow you to
define more than one owner for input modules.
NOTE
IMPORTANT
: Only input modules can have multiple owners. If multiple
owners are connected to the same input module, they must
maintain
identical configurations
for that module.
In the example below, Controller A and Controller B have both been configured
to be the owner of the input module.
When the controllers begin downloading configuration data, both try to establish
a connection with the input module. Whichever controller’s data arrives first
establishes a connection. When the second controller’s data arrives, the module
compares it to its current configuration data (the data received and accepted from
the first controller).
If the configuration data sent by the second controller matches the configuration
data sent by the first controller the connection is also accepted. If any parameter
of the second configuration data is different from the first, the module rejects the
connection, and the user is informed by an error in the software.
The advantage of multiple owners over a ‘Listen-only’ connection is that now
either of the controllers can lose the connection to the module and the module
will continue to operate and multicast data to the system because of the
connection maintained by the other owner-controller.
NOTE
The previous discussion of multiple owners assures the configuration tag
.ConfigurationRevNumber is set to 1. Operation differs if the tag is set to
0. Refer to Chapter 5 for descriptions of this tag’s settings.
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