Allen-Bradley 1757-FFLD2, User Manual

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104 Rockwell Automation Publication 1757-UM012A-EN-P - July 2011
Chapter 6 Logix Block Operation in a ControlLogix System
Scheduled Logix Block
Modules Connected
through ControlNet
Network (1757-FFLDC
linking device) When Logix Block modules are connected to the owner-controller through a
scheduled ControlNet network, the value of the RPI determines how often the
owner-controller will receive the data over the network.
The RPI value specified for a Logix Block module connected by a scheduled
ControlNet network ‘reserves’ a spot in the stream of data flowing across the
ControlNet network.
The timing of a ‘reserved’ spot may or may not coincide with the exact value of
the RPI, but the control system guarantees that the owner-controller receives data
at least as often as the specified RPI.
Listen-only Mode
Any controller in the system can listen to the data from a Logix Block module
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 the
Listen Only - Data mode in the Communication Format field.
Choosing the Listen Only - Data mode allows the controller and module to
establish communication 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.
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.