110 Rockwell Automation Publication 1769-UM011H-EN-P - April 2012
Chapter 7 Develop Applications
•The controller performs service communication for up to 1 ms at a time and
then resumes the continuous task.
To select a system overhead percentage, perform this procedure.
1. In the Controller Organizer of RSLogix 5000 programming software,
right-click on your controller and choose Properties.
The Controller Properties dialog box appears.
2. Click the Advanced tab.
3. From the System Overhead Time Slice menu, choose a percentage.
System overhead time slice functions include:
• communicating with programming and HMI devices, such as RSLogix
5000 software.
• responding to messages.
• sending messages.
The controller performs system overhead functions for up to 1 millisecond
at a time. If the controller completes the overhead functions in less than
one millisecond, it resumes the continuous task.
As the system overhead time slice percentage increases, time allocated to
executing the continuous task decreases. If there are no communication for
the controller to manage, the controller uses the communication time to
execute the continuous task. While increasing the system overhead
percentage does increase communication performance, it also increases the
amount of time it takes to execute a continuous task, increasing overall
scan time.
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