Rockwell Automation Publication 2080-UM002K-EN-E - March 2019 297
User Interrupts Appendix D
Using the Selectable Timed
Interrupt (STI) Function
Configure the STI function from the Interrupt Configuration window.
The Selectable Timed Interrupt (STI) provides a mechanism to solve time critical
control requirements. The STI is a trigger mechanism that allows you to scan or
solve control program logic that is time sensitive.
Example of where you would use the STI are:
· PID type applications, where a calculation must be performed at a specific
time interval.
· A block of logic that needs to be scanned more often.
How an STI is used is typically driven by the demands/requirements of the
application. It operates using the following sequence:
1. The user selects a time interval.
2. When a valid interval is set and the STI is properly configured, the
controller monitors the STI value.
3. When the time period has elapsed, the controller’s normal operation is
interrupted.
4. The controller then scans the logic in the STI POU.
5. When the STI POU is completed, the controller returns to where it was
prior to the interrupt and continues normal operation.
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