Siemens SIMATIC S7-1500 System Manual page 378

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 12-5
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.
Advantages:
• During downloading, the primary CPU maintains control of the process. The plant remains
in operation.
• Restore the previous user program:
After loading in the RUN-Solo operating mode, the backup CPU is in the STOP mode The
previous user program is still on the backup CPU.
If you want to restore the previous user program, then switch the primary CPU to the STOP
operating mode and then the backup CPU to the RUN operating state. Result: The backup
CPU with the previous user program starts as primary CPU.
Then switch the backup CPU to the RUN operating state. Result: The redundant system
with the previous user program is in the system state Run-Redundant.
Note
If you restore the previous user program, the procedure describes leads to the STOP
system of the redundant system.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF
"Extended download" dialog window (backup CPU)
Commissioning
12.3 Commissioning procedure
377