Siemens SIMATIC S7-1500 System Manual page 121

System overview
5.4 Communication
Response of S7-1500R
When a CP fails, the corresponding CPU changes to STOP mode. The S7-1500R system
changes to the RUN-Solo system state.
When the CP at the primary CPU fails, the S7-1500R redundant system performs a primary-
backup switchover. The assigned system IP address changes to the new primary CPU.
Establishing the new communication connection then takes place via the redundant CP.
If the CP at the backup CPU fails, this failure has no effect on the existing communication via
the system IP address.
Behavior of S7-1500H with active backplane bus
When a CP fails, the S7-1500H system remains in the RUN-Redundant system state.
If the CP at the primary CPU fails, the redundant S7-1500H system does not perform a
primary-backup switchover. In this case, establishing a new communication connection via
the redundant CP is only possible via the assigned device IP address.
Alternatively, you can set up a primary-backup switchover in the user program. To do this,
call the "RH_CTRL" instruction with Mode=8 in the user program. This requests STOP mode of
the primary CPU. The backup CPU becomes the primary CPU and changes to RUN mode. The
W1 system IP address also changes to the new primary CPU. The establishment of the new
communication connection then takes place automatically via the redundant CP.
You can find more information about the "RH_CTRL" instruction in the online help for STEP 7.
You can find information on configuring the system IP address for the virtual W1 interface
and virtual MAC address in the Configuring R-CPUs with communications
processor CP 1543-1 (Page 304) section.
More information
You can find more information on the system IP address in the S7-1500R/H redundant system
in the Communication (https://support.industry.siemens.com/cs/ww/en/view/59192925)
Function Manual.
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S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF