Technical data

Appendix
27.1 Operating Modes
Programming with STEP 7
562 Manual, 05/2010, A5E02789666-01
Automatic Warm Restart
An automatic warm restart can be triggered following power up in the following situations:
• The CPU was not in STOP mode when the power outage occurred.
• The mode selector is set to RUN or RUN-P.
• No automatic hot restart is programmed following power up.
• The CPU was interrupted by a power outage during a warm restart (regardless of the
programmed type of restart).
The CRST/WRST switch has no effect on an automatic warm restart.
Automatic Warm Restart Without a Backup Battery
If you operate your CPU without a backup battery (if maintenance-free operation is necessary), the
CPU memory is automatically reset and a warm restart executed after the power is turned on or
when power returns following a power outage. The user program must be located on a flash
EPROM (memory card) and there must be no battery monitoring set with the "Batt.Indic" switch on
the power supply.
Hot Restart
Following a power outage in RUN mode followed by a return of power, S7-400 CPUs run through
an initialization routine and then automatically execute a hot restart. During a hot restart, the user
program is resumed at the point at which its execution was interrupted. The section of user
program that had not been executed before the power outage is known as the remaining cycle. The
remaining cycle can also contain time-driven and interrupt driven program sections.
A hot restart is only permitted when the user program was not modified in STOP mode (for
example, by reloading a modified block) and when there are no other reasons for a warm restart.
Both a manual and automatic hot restart are possible.
Manual Hot Restart
A manual hot restart is only possible with the appropriate parameter settings in the parameter set
of the CPU and when the STOP resulted from the following causes:
• The mode selector was changed from RUN to STOP.
• User-programmed STOPs, STOPs after calling OBs that are not loaded.
• The STOP mode was the result of a command from the programming device or a
communication function.
A manual hot restart can be triggered by the following:
• The mode selector
The CRST/WRST must be set to WRST.
• The corresponding command on the programming device or by communication functions
(mode selector set to RUN or RUN-P).
• When a manual hot restart is set in the parameter set of the CPU.