18 Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Chapter 1 Analog I/O Module Operation in the ControlLogix System
The following graphic shows an Event task dialog box in Logix Designer
application.
Event tasks are useful for synchronizing process variable (PV) samples and
proportional integral derivative (PID) calculations.
For more information on Event tasks, see the Logix5000 Controllers Tasks,
Programs, and Routines Programming Manual, publication 1756-PM005
.
Output Module Operation
The RPI defines when a controller sends data to the analog output module and
when the output module echoes data. The controller sends data to an output
module only at the RPI.
When an output module receives new data from the controller, the module
multicasts or ‘echoes’ a data value that corresponds to the signal present at its
terminals to the rest of the control system. This feature, called Data Echo, occurs
whether the output module resides in the local or remote chassis.
Depending on the value of the RPI, regarding the length of the controller
program scan, the output module can receive and ‘echo’ data multiple times
during one program scan.
When the RPI is less than the program scan length, the module’s output channels
can change values multiple times during one program scan. The controller does
not depend on reaching the end of the program to send data.
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