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.
*Exception: In the RUN-Redundant system state, a higher-priority OB 83 "Pull/plug modules"
does not interrupt the execution of an OB 82 "Diagnostic interrupt".
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.
Reference
Additional information on organization blocks is available in the STEP7 online help.
9.4 Special instructions for S7-1500R/H redundant systems
9.4.1 Disabling/enabling SYNCUP with the RH_CTRL instruction
Introduction
You use the "RH_CTRL" instruction to disable SYNCUP or to enable the execution of the
SYNCUP for the S7‑1500R/H redundant system. The disable applies:
•
Until you cancel it with the "RH_CTRL" instruction or
•
Until the S7‑1500R/H redundant system switches to the STOP system state
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S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD
Basics of program execution
9.4 Special instructions for S7-1500R/H redundant systems
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