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Control I/O Chapter 4
Communication Format
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
Table 9 - Communication Formats
Communication Format with a
Remote ControlNet
Communication Module
Criteria for Use
None • 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
Rack-optimized
• 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
Rack-optimized—Listen only 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.
Table 10 - Communication Format for Module Types
I/O Module Type Desired Connection Required Communication Format
Digital module Rack-optimized connection Rack-optimized
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
• 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.
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
• 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.
Rockwell Automation Publication CNET- UM001E-EN-P - June 2016 57