Siemens SIMATIC S7-1500 System Manual page 76

Principle of operation
Unlike in S7-1500R, the PROFINET ring (PROFINET network) and redundancy connections in
S7-1500H are separate. The two redundancy connections are fiber-optic cables that connect
the CPUs directly over synchronization modules.
One of the two CPUs in the redundant system takes on the role of primary CPU. The other
CPU takes on the role of the following CPU (backup CPU). The role of the CPUs can change
during operation.
Synchronization of primary and backup CPU ensures rapid switchover between CPUs in the
event of a failure of the primary CPU. If the primary CPU fails, the backup CPU takes over
control of the process as the new primary CPU.
The synchronization of the H-CPUs does not affect the bandwidth on the PROFINET.
Reference
You can find more information and configuration variants (e.g. combined topologies) of the
S7-1500H redundant system in the Specific configuration variants of the S7-1500H
redundant system (Page 150) section.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF
5.1 What is the S7-1500R/H redundant system?
System overview
75