Siemens Simatic S7-1500 Function Manual page 61

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
Extension of the cycle
As with non-redundant CPUs, an occurring event and the associated OB can extend the
cycle. Events can occur both during the execution of the cyclic program and during the time
lag.
In the following example the CPU must process a higher-priority OB (OB 30 with priority 7),
while the primary CPU waits for the end of the cycle of the backup CPU. The figure below
shows the phases which the CPUs run through in such a case.
①
Cycle time
②
Cycle of the backup CPU
③
Time lag
④
Cycle end and start of the next cycle (cycle control point)
Figure 5-3 Processing of a higher-priority OB
60
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD