If your Logic program is configured to execute On Interval (see Define the Execution Method for a Logic Program), you can use the Trigger setting to associate the Logic program with any property of any database item. When there is a change to the value of the selected property, the Logic program will execute.
If the Logic program is set to have an Execute Method of On Interval, the time specified for the Interval defines how often the program checks the value of the Trigger item. For example, if the Interval is 30S, the program will check the value of the Trigger item every 30 seconds, and the program will only execute if the value of the Trigger item has changed.
The Trigger feature is useful when you need a Logic program to execute as a response to the value or state of a database item that is not used as an input in the program. For example, you may have a Logic program that uses various points as inputs, but is triggered by the state of the outstation with which those points are associated. The outstation state is not defined as an input in the program (as it is not relevant to the program), but when the state of the outstation changes, the Logic program executes.
You can set a Logic program to execute in response to a change to any property field in the database. To do this, display the Logic Program Form, select the Logic tab, then use the browse button feature of the Trigger field to select the required property. When the value of the selected property changes, the Logic program will be executed.
Further Information
Display the Logic Program Form: see Configure an ST Program, Ladder Diagram, SFC or FBD.