Siemens SIMATIC S7-1500 System Manual page 377

Commissioning
12.3 Commissioning procedure
Note
Role change during loading
Beware of a possible role change between primary and backup CPU shortly before, during or
after loading.
A role change can occur during loading if the primary CPU fails (power failure, hardware
defect) or is in STOP and:
• You switch the backup CPU to RUN operating state during this time using the mode
selector, the display or a communication command.
or
• You switch on the backup CPU during this time.
In the event of a role change, the new primary CPU starts up with the old project data. The
new project data in the backup CPU is overwritten with the old project data during
synchronization of the two CPUs for redundant operation.
Downloading project data to the backup CPU
You can also download the project data to the backup CPU. This makes sense if the backup
CPU is to be primary CPU with its project data upon a restart.
Requirement
The backup CPU is in STOP mode.
Procedure:
1. Download the project data to the backup CPU. The primary CPU continues to control the
process.
2. Switch the primary CPU to the STOP operating state after loading.
3. Switch the backup CPU to the RUN operating state. It becomes the new primary CPU and
controls the process on its own with the newly loaded user program in the RUN-Solo system
state.
4. Switch the new backup CPU to the RUN operating state.
Result: The system state is RUN-Redundant.
Note
Please note the following during download to the backup CPU:
If the project uses retentive data, the backup CPU runs with its data which may be outdated.
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S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF