Technical data

Basics of Designing a Program Structure
4.2 Blocks in the User Program
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 107
Startup Type After Automatic Restart
On S7-300 CPUs, only a restart (warm restart) is possible following power up.
On S7-400 CPUs, you can specify whether an automatic startup following power up leads to a
restart (warm restart) or a hot restart.
Clearing the Process Image
When an S7-400 CPU is restarted, the remaining cycle is executed, and as default, the process
image output table is cleared. You can prevent the process image being cleared if you want the
user program to continue with the old values following a restart.
Module Exists/Type Monitoring
In the parameters, you can decide whether the modules in the configuration table are checked to
make sure they exist and that the module type matches before the startup.
If the module check is activated, the CPU will not start up if a discrepancy is found between the
configuration table and the actual configuration.
Monitoring Times
To make sure that the programmable controller starts up without errors, you can select the
following monitoring times:
• The maximum permitted time for transferring parameters to the modules
• The maximum permitted time for the modules to signal that they are ready for operation after
power up
• On S7-400 CPUs, the maximum time of an interruption during which a hot restart is permitted.
Once the monitoring times expire, the CPU either changes to STOP, or only a restart (warm
restart) is possible.