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Using Message Instructions
Ladder logic uses message instructions to change the module configuration
during module operation.
Message instructions maintain these characteristics:
•
messages use unscheduled portions of system communication
bandwidth
•
one service is performed per instruction
•
performing module services does not impede module functionality, such
as counting incoming pulses
Processing Real-Time Control and Module Services
Because message instructions use unscheduled portions of systems
communication bandwidth, the services requested of a module are not
guaranteed to occur within a specific time period. Although the module
response typically occurs in less than a second, there is no specific time
interval that reflects this response.
One Service Performed Per Instruction
Message instructions only cause a module service to be performed once per
execution. For example, if a message instruction sends new configuration data
to the module, the message instruction must be reexecuted to update send the
configuration data in the future.
Rockwell Automation Publication 1756-UM010C-EN-P - June 2021
Chapter 5
Configure the Configurable Flowmeter Module
81
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