Technical data

Appendix
27.1 Operating Modes
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 563
Automatic Hot Restart
An automatic hot restart can be triggered following power up in the following situations:
• The CPU was not in STOP or HOLD mode when the power outage occurred.
• The mode selector is set to RUN or RUN-P.
• Automatic hot restart following power up is set in the parameter set of the CPU.
The CRST/WRST switch has no effect on an automatic hot restart.
Retentive Data Areas Following Power Down
S7-300 and S7-400 CPUs react differently to power up following a power outage.
S7-300 CPUs (with the exception of the CPU 318) are only capable of a warm restart. With STEP
7, you can, however, specify memory bits, timers, counters, and areas in data blocks as retentive
to avoid data loss caused by a power outage. When the power returns, an automatic warm restart
with memory is executed.
S7-400 CPUs react to the return of power depending on the parameter settings either with a warm
restart (following retentive or non-retentive power on) or a hot restart (only possible following
retentive power on).
The following table shows the data that are retained on S7-300 and S7-400 CPUs during a warm
restart, cold restart, or hot restart.
X means data retained
VC means logic block retained in EPROM, any overloaded logic blocks are lost
VX means data block is retained only if on the EPROM retentive data are taken from the NV-RAM
(loaded or created data blocks in the RAM are lost)
0 means data are reset or erased (content of DBs)
V means data are set to the initialization value taken from the EPROM memory
--- means not possible as no NV-RAM available