Rockwell Automation Publication 1756-UM535D-EN-P - November 2012 163
Program the Redundant Controller Chapter 7
Program to Optimize Task
Execution
To make synchronization, crossloads, and HMI updates as fast as possible, make
adjustments to the System Overhead Time Slice and the type of tasks used. These
adjustments affect service communication tasks that take place during the time
when the continuous task is not executing.
This table lists some of the communication that takes place during an continuous
task and service communication periods.
To increase service communication to allow for synchronization and the
updating of HMI, consider using the techniques described in this table.
Table 26 - Communication Tasks during Scheduled and Unscheduled Periods
During These types of communication occur
Task execution Update I/O data (not including block-transfers)
Produced/consumed tags
Service
communication
Communication with programming devices (for example, RSLogix 5000 software)
Communication with HMI devices
Execution of Message (MSG) instructions, including block-transfers
Responses to messages from other controllers
Synchronization of the redundant system
Reestablishment and monitoring of I/O connections, such as Removal and Insertion Under
Power conditions. This does not include normal I/O updates that occur during the execution of
logic
Bridging of communication from the serial port of the controller to other ControlLogix devices
via the ControlLogix backplane
Table 27 - Methods to Increase Service Communication Periods
If your RSLogix 5000 project contains Then see On Page
Only a continuous task with no other tasks (This is the
default task configuration.)
Specify a Larger System Overhead Time
Slice
164
More than one task (for example, at least 2 periodic tasks) Use Periodic Tasks 167
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