Siemens SIMATIC S7-1500 System Manual page 260

Commissioning
11.3 Commissioning procedure
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If the project uses retentive data, the backup CPU runs with its data which may be outdated.
Detailed procedure for download to the backup CPU:
1. Right-click to select the S7-1500R/H system in the project tree.
2. Select "Hardware and software (changes only)" under "Download to backup CPU".
The backup CPU is now selected instead of the primary CPU in the "Extended download"
dialog window.
Figure 11-5 "Extended download" dialog window (backup CPU)
Load user program in RUN-Solo system state
The redundant system is in the RUN-Redundant system state. You can download a modified
user program to the primary CPU.
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S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD