Siemens SIMATIC S7-1500 System Manual page 326

OB 86
There are three IO devices in the example. Each failure of one of the three IO devices is
followed by recovery of the IO device. Each IO device failure/IO device recovery is signaled.
Cyclic program execution is interrupted with an OB 86 call.
In the "Copy main memory" phase of the SYNCUP system state those OBs that interrupt the
cyclic program processing are processed. New diagnostic events are signaled but the OBs are
not yet processed. In the example, the failure of IO device 2 and the recovery of IO device 3
are signaled. However, the OB 86 are not processed until the following phase, "Making up
backup CPU lag".
Note
Order of execution of OB 86
Please note that the order of processing of the OB 86 may differ from the order of processing
of the associated diagnostic events.
Note
Station re-integration with errors
When a station returns with errors in an R/H-CPU, no attempt is made - in contrast to a
standard CPU - to output exact error information in the diagnostic buffer.
OB 72
If the system then switches to the RUN-Redundant system state, OB 72 "CPU redundancy
error" is called. OB 72 is called again:
• If the redundant system exits redundant operation and changes to the RUN-Solo system
state.
• If the redundant system is in redundant operation and the synchronization of the two
R/H-CPUs is no longer possible redundantly or is possible redundantly again.
All cases can be distinguished by the start information of OB 72. You can find more
information on this topic in the STEP 7 online help.
Note
Delayed execution of OB 72
There may also be a delay in executing OB 72 because the corresponding diagnostic event is
processed asynchronously to the user program.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF
Basics of program execution
10.3 Events and OBs
325