Communication Format - Allen-Bradley ControlNet ControlLogix 1756 User Manual

Communication Format

Table 9 - Communication Formats
Communication Format with a
Remote ControlNet
Communication Module
None
Rack-optimized
Rack-optimized—Listen only
Table 10 - Communication Format for Module Types
I/O Module Type Desired Connection
Digital module Rack-optimized connection
Direct connection or to use specialty features of
the module, such as diagnostics, timestamps, or
electronic fuses
or
Connection for listening to data from the module
Analog module Direct connection or to use specialty features of
the module, such as diagnostics, timestamps, or
electronic fuses
or
Connection for listening to data from the module
When you configure a remote ControlNet communication module or an I/O
module, you choose a communication format. The chosen communication
format determines the data structure for tags associated with the module. Many
I/O modules support different formats. Each format uses a different data
structure.
The chosen communication format also determines the following:
•
Direct or rack-optimized connection
Ownership of outputs
•
Criteria for Use
• When all of the remote I/O communicating with a controller via the remote ControlNet communication module
use a Direct Connection communication format
• When the connection is used for scheduled peer interlocking
• When I/O will be mostly direct connections
• When multiple controllers control the outputs in the chassis
• When some or all of the remote I/O communicating with a controller via the remote ControlNet communication
module use a rack-optimized communication format
• To minimize ControlNet network bandwidth when using large volume of digital I/O
• If only one controller will control the I/O
When some or all of the remote I/O communicating with a controller via the remote ControlNet communication
module use a rack-optimized communication format
I/O module type determines the available communication formats.
Rockwell Automation Publication CNET-UM001E-EN-P - June 2016
Required Communication Format
Rack-optimized
• The data your controller needs from the I/O module. For example, if your
application uses a 1756-IA16I module in a remote chassis that must
provide timestamped input data, choose the CST Timestamped Input Data

communication format.

• A listen-only communication format that matches the data the I/O module
is broadcasting to other controllers.
• The data your controller needs from the I/O module. For example, if your
application uses a 1756-OF6CI module in a remote chassis that must
provide floating point output data, choose the Float Data communication
format.
• A listen-only communication format that matches the data the I/O module
is broadcasting to other controllers.
Control I/O Chapter 4
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