Programming
Fail-Safe Systems
5-50 A5E00085588-03
Permissible Changes
Below you can find a list of the permissible program changes. These changes can
be downloaded when safety mode is deactivated, without the Safety Program
going into shutdown mode. The restrictions listed below, however, continue to
apply:
• Any local changes to run-time groups.
Local changes are changes that do not involve changes to the communication
between run-time groups or CPUs. Within the run-time group any
interconnections and constants can be changed and blocks can be deleted,
reinserted or moved in the run sequence within the run-time group.
• Deletion of complete run-time groups:
Run-time groups must only be deleted individually. After a run-time group has
been deleted, you must recompile the program and download the changes.
• Insertion of new run-time groups
• Changes to the priority classes.
The monitoring times must be taken into consideration (see below).
- Changes to the OB cycle time (parameter assignment of the CPU is
supported for the S7-400FH with the CPU 417-4H, V2.0 and above).
- Movement of run-time groups (deletion and insertion) to new tasks/OBs.
!
Safety Note – OB Cycle Times Changes Restricted
You must not change OB cycle times or move run-time groups unless the time and
speed relationships change as well. This means that the tasks that used to be the
slowest and fastest must continue to be so after the changes have been
downloaded.
If they are not, it may not be possible to deactivate safety mode, or the Safety
Program might shutdown when changes are downloaded. In this case, any
changes cannot be reversed, and you have to revert to a previously saved Safety
Program ).
• It is possible to move run-time groups to another task. The monitoring times
must be taken into consideration (see below).
Some operations require several steps because the new Safety Program cannot
be activated all at once. Instead, it has to be activated in several steps (see below).
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