Technical data

Appendix
27.1 Operating Modes
Programming with STEP 7
568 Manual, 05/2010, A5E02789666-01
Key to the figure "Activities of the CPU during STARTUP and RUN"
1. All peripheral outputs are switched to a safe state (default value = 0) on the hardware side by
the I/O modules. This switch takes place regardless of whether the user program employs the
outputs inside the process-image area or outside of it.
If you are using signal modules that have substitute value capability, you can assign
parameters to the behavior of the outputs, such as Keep Last Value.
2. Necessary for processing the remaining scan cycle.
3. A current process-image input table is also available to the interrupt OBs the first time that they
are called up.
4. You can determine the status of the local and distributed peripheral outputs in the first scan
cycle of the user program by taking the following steps:
- Use output modules to which you can assign parameters to enable the output of substitute
values or to keep the last value.
- For a hot restart: activate the CPU startup parameter "Reset outputs during hot restart" in
order to output a 0 (corresponds to the default setting).
- Preset the outputs in the startup OB (OB100, OB101, OB102).
5. In S7-300 systems that are not backed up, only those DB areas that were configured as
retentive are retained.