Siemens SIMATIC S7-1500 System Manual page 415

Commissioning
12.4 Operating and system states
(2) Primary-backup switchover
Figure 12-12 Primary-backup switchover
Table 12- 15 Response to primary CPU error: Backup CPU becomes primary CPU and switches to RUN
No. in CPU 1
diagram
Initial situation: The S7-1500R/H redundant system is in the RUN-Redundant system state.
The primary CPU (CPU 1) fails because of a hardware defect.
① Following the failure, CPU 1 switch-
es from the RUN-Redundant operat-
ing state to STOP or POWER OFF.
Error elimination procedure for redundant operation
1. Eliminate the error.
2. Start CPU 1.
CPU 1 becomes the backup CPU and switches from the STOP operating state to the SYNCUP
operating state.
Synchronization starts as detailed in the section SYNCUP system state (Page 388).
414
System state
RUN-Redundant → RUN-Solo
CPU 2
CPU 2 becomes primary CPU and switch-
es to the RUN operating state. The CPU
behaves like a standard CPU and contin-
ues to process the user program.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF