Siemens SIMATIC S7-1500 System Manual page 279

You can find a detailed list of the causes of error and remedies in the table SYNCUP abort:
Causes and solutions.
Figure 11-8 SYNCUP system state aborts
Table 11-12 Sequence of events: SYNCUP aborts
No. in Primary CPU
diagram
Initial situation: The S7-1500R/H redundant system is in the SYNCUP system state. An error occurs in the backup CPU.
The CPU does not switch from the RUN-Syncup
①
operating state to RUN-Redundant, but instead
returns to RUN and continues to execute the
user program.
Procedure for error correction
1. Eliminate the error.
2. Switch the backup CPU from STOP to RUN.
The backup CPU switches from STOP to the SYNCUP operating state. Synchronization restarts.
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD
System state
SYNCUP → RUN-Solo
Commissioning
11.4 Operating and system states
Backup CPU
If SYNCUP aborts, the backup
CPU may restart and then switch
to the STOP operating state. The
backup CPU is ready for a new
SYNCUP.
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