Siemens SIMATIC S7-1500 System Manual page 224

Basics of program execution
9.3 Events and OBs
The call of OB 86 indicates the station return, independent of the redundancy status of the
R1/S2 device at the time of the call of OB 86.
• If both ARs can be established on return, OB 70 is called after OB 86. The R1/S2 device is
redundant.
• If only one AR can be set up on return, no OB 70 is called. The R1/S2 device is not
redundant.
Priority of OB 70 and OB 86
NOTE
Priority of OB 70 and OB 86
Select the same priority for OB 70 and OB 86 or keep the default setting (priority 6). This
prevents the OBs from interrupting each other. The user program processes events of the
same priority in order of occurrence.
Behavior of the OB 70 and the OB 86 after SYNCUP
If an R1/S2 device becomes redundant after the system state RUN-Redundant has been
accessed, OB 70 (outgoing) is called.
If an IO device is only accessible by the backup CPU and was not reachable at all before the
SYNCUP, then in the system state RUN-Redundant OB 86 (outgoing) is called, but not OB 70.
This indicates the return of the IO device without redundancy.
Example: OB 72 CPU redundancy failure
Automation task
You use the S7-1500R redundant system to control a blast furnace. The S7-1500R redundant
system controls the blast furnace temperature, volume and pressure parameters.
Feature
In the event of a loss of redundancy, for example because the primary CPU fails, a signal lamp
in the blast furnace control room signals this event. The control room notifies the service
personnel. The service personnel replace the defective CPU.
Solution
OB 72 is called in the event of a CPU redundancy error. The user program in OB 72 controls a
digital output module (relay) in an ET 200SP with a connected signal lamp.
Response of S7-1500R/H redundant system when cycle time is exceeded
The tables below show how the redundant system responds when the cycle time is exceeded.
If the user program does not reach the cycle control point within the maximum cycle time,
the redundant system responds as described in the column "1st time cycle time is exceeded".
The redundant system then resets the cycle time monitoring.
224
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD