Siemens Simatic S7-1500R System Manual page 83

Application planning
3.5 Failure scenarios
Sequence of events
1. An IO device in the PROFINET ring fails.
2. As a result, the PROFINET ring is interrupted.
3. The redundant system selects an alternative connection over the backup CPU. This
allows the redundant system to access all remaining IO devices in the PROFINET ring
again.
4. The primary CPU also fails.
5. The redundant system does not switch to the backup CPU and switches to the STOP
system state. The role of the backup CPU remains unchanged.
Note
The backup CPU does not differentiate between the following scenarios:
• It can no longer access the primary CPU because the latter has failed.
• The PROFINET ring has been interrupted at a second point and the primary CPU may
That is why the backup CPU does not become the primary CPU. This prevents an
undefined system state.
6. The redundant system has failed. The process is no longer controlled by the redundant
system.
Diagnostics
System state, operating states and error displays after the failure of the IO device in the
PROFINET-Ring and the STOP of Backup CPU:
● Redundant system → STOP system state
● Primary CPU → failed
● Backup CPU → STOP operating state
– MAINT LED → yellow light: The R system is not in the RUN-Redundant system state.
– ERROR LED → flashes red: One or more IO devices have failed.
Note
To get detailed diagnostics information, evaluate the diagnostics buffer.
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still be running.
No partner CPU has been found in the R system. The PROFINET ring is open.
S7-1500R/H redundant system
System Manual, 10/2018, A5E41814787-AA