Technical data

Testing with the Variable Table
20.7 Modifying Variables
Programming with STEP 7
460 Manual, 05/2010, A5E02789666-01
20.7.2 Defining the Trigger for Modifying Variables
You can assign fixed values to individual variables of a user program (once or every cycle) at a
specific point during program processing (trigger point).
When you select a trigger point you determine the point in time at which the modify values are
assigned to the variables.
You can set the trigger point and a trigger frequency using the menu command Variable > Trigger.
Trigger Possible Settings
Trigger point Start of cycle
End of cycle
Transition from RUN to STOP
Trigger frequency Once
Every cycle
Trigger Point
The following figure shows the position of the trigger points.
The position of the trigger points shows:
• Modifying inputs is only useful with the trigger point "Start of cycle" (corresponds to the start of
the user program OB 1), because otherwise the process image of the inputs is updated after
modifying and therefore overwritten).
• Modifying outputs is only useful with the trigger point "End of cycle" (corresponds to the end of
the user program OB 1), because otherwise the user program can overwrite the process image
of the outputs).
To display the modified value in the "Status Value" column, you should set the trigger point for
monitoring to "Start of cycle" and the trigger point for modifying to "End of cycle".