Spectrum Controls 1756sc-OF8H Series A - Manual (Page 37)

Chapter 3: Operation within the System 23
any configuration data. In this instance, another controller owns the
module being listened to.
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.
Multiple Owners of
Input Modules
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.
Important: Only input modules can have multiple owners. If multiple
owners are connected to the same input module, they must maintain
identical configuration 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 assumes the
configuration tag “.configrevnumber” is set to 1. Operation differs is
the tag is set to 0. Refer to Chapter 5 for descriptions of this tag’s
settings.