Siemens SIMATIC S7-1500 System Manual page 264

Commissioning
11.4 Operating and system states
Event-controlled synchronization
Event-controlled synchronization ensures that both CPUs in a redundant system can operate
redundantly (RUN-Redundant system state).
For all events that could result in different internal subsystem states, the operating system
automatically synchronizes the data of the primary and backup CPU.
Primary and backup CPU are, for example, synchronized in the event of:
• Direct access to the IO devices
• Events that interrupt cyclic program execution
• Updates to user times, for example S7 timer
• Updates to the process image
• Changes to data through communication functions
• Access to data that could be different on the different CPUs, for example current time,
system time, or runtime messages
Synchronization for redundant mode
In the SYNCUP system state, the operating system synchronizes the user programs in the two
CPUs for redundant operation.
Synchronization ensures that both CPUs can operate redundantly. In the event of failure of
the primary CPU in redundant operation, the backup CPU takes over control of the process as
the new primary CPU at the point of interruption.
Requirements for achieving a redundant system state
If the following requirements are met, the redundant system reaches the RUN-Redundant
system state:
• The requirements for use of the S7-1500R/H redundant system have been met (see
section Application planning (Page 72)).
• The two CPUs of the redundant system have recognized each other, which means pairing
was successful (see section CPU pairing (Page 250));
• You have commissioned the system as detailed in the section Commissioning procedure
(Page 246).
Overview of system and operating states
The figure below shows the possible operating states of the CPUs and the resulting system
states.
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S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD