Siemens SIMATIC S7 F Manual page 146

Programming
6. Close the "Select Structure Element" dialog box. If the change is possible, a
check box appears with the changed value, which you have to confirm with
OK.
7. If the change is not possible, you will receive a message requesting you to
eliminate the cause of the error. You then have to repeat steps 3 to 6.
Result: The new value is downloaded to the CPU and displayed at the I/O.
It is not possible to compile and download changes after CFC test mode has been
deactivated until safety mode has been activated, because all the necessary
changes were made when each individual parameter was changed.
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Fail-Safe Systems
A5E00085588-03