Siemens Simatic S7-1500 Function Manual page 62

Execution of the cyclic program (CP with priority 1) is complete. While the primary CPU waits
for the end of the cycle of the backup CPU, a higher priority OB (OB 30 with priority 7) starts.
The primary CPU starts the next cycle as soon as the following conditions have been
fulfilled:
● The primary CPU has received the message from the backup CPU that the backup CPU
has finished processing the cyclic program.
● The primary CPU has processed OB 30 and updated PIPQ1.
Note
Due to the change of the run level and the synchronization, interruptions of the program
cycle by higher-priority OBs result in a higher load. Interruptions of the program cycle extend
the cycle time.
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD
Cycle and response times of the S7-1500R/H redundant system
5.3 Influences on the cycle time of the S7-1500R/H redundant system
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