Safety in F-Systems
4.4 Restart of F-System
Safety Engineering in SIMATIC S7
4-6
System Manual, 04/2006, A5E00109529-05
4.4
4.4
Restart of F-System
F-System Operating Modes
The operating modes of S7 Distributed Safety and S7 F/FH Systems differ from those of
standard systems only in terms of the restart characteristics and the behavior in HOLD
mode.
Restart Characteristics
When an F-CPU is switched from STOP to RUN mode, the standard user program restarts
in the usual way. When the safety program is restarted, the following data blocks are
initialized with values from the load memory:
•
For S7 Distributed Safety: all data blocks with the F-attribute
•
For S7 F/FH Systems: all data blocks
This occurs analogously to a cold restart. As a result, saved error information is lost.
The F-system automatically reintegrates the F-I/O. In contrast to the standard user program,
restart OBs (OB 100 to OB 102) cannot be used in the safety program.
Restart Protection
A data handling error or an internal fault can also trigger a safety program restart with the
values from the load memory. If your process does not allow such a startup, you must
program a restart/startup protection in the safety program: Process data outputs must be
blocked until manually enabled. The process data output block must not be released until it
is safe to do so and faults have been corrected.
HOLD Mode
HOLD mode is not supported for S7 Distributed Safety and S7 F/FH Systems. If a HOLD
request stops execution of the user program, this state can only be overridden by a restart
(cold restart or warm restart).
