Siemens Simatic S7-1500R System Manual page 157

Basics of program execution
7.3 Events and OBs
Table 7- 4 Response of S7-1500R/H redundant system when cycle time is exceeded with OB 80
Initial situation
System Primary Backup
CPU CPU
RUN- RUN STOP
Solo
RUN- RUN- SYNCUP
Syncup Syncup
RUN- RUN- RUN-
Redun- Redun- Redun-
dant dant dant
OB 80 is not called until the cycle time is exceeded for the first time after the SYNCUP phase "Finish tasks".
1)
Assignment between event source and OBs
The type of OB determines where you assign OB to event source:
● For hardware interrupts: Assignment in hardware configuration
● For all other OB types: Assignment when the OB is created, where applicable after you
have configured the event source
OB priority and runtime behavior
If you have assigned an OB to the event, the OB has the priority of the event. S7-1500R/H
CPUs support the priorities 1 (lowest) to 26 (highest). The following items are essential to the
execution of an event:
● Call and execution of the assigned OB
● The update of the process image partition of the assigned OB
The user program processes the OBs exclusively on a priority basis. This means the
program processes the OB with the highest priority first when multiple OB requests occur at
the same time. If an event occurs that has a higher priority than the currently active OB, this
OB is interrupted. The user program processes events of the same priority in order of
occurrence.
Note
Communication
Communication (for example test functions with the PG/PC) always operates with a priority
of 15. To avoid unnecessarily prolonging the program runtime in the case of time-critical
applications, make sure that these OBs are not delayed or interrupted by communication.
Assign a priority > 15 for these OBs.
156
1st time cycle time is ex-
ceeded
System Primary Backup
CPU CPU
RUN- RUN + STOP
Solo OB 80
RUN- RUN- SYNCUP
Syncup Syncup + OB 80
+ OB 80
1)
RUN- RUN- RUN-
Redun- Redun- Redun-
dun- dant + dant +
dant OB 80 OB 80
2nd time cycle time is ex-
ceeded
System Primary Backup
CPU CPU
STOP STOP STOP
RUN- RUN + STOP
Solo OB 80
RUN- RUN + STOP
Solo OB 80
System Manual, 10/2018, A5E41814787-AA
3rd time cycle time is ex-
ceeded
System Primary Backup
CPU CPU
--- --- ---
STOP STOP STOP
STOP STOP STOP
S7-1500R/H redundant system