S7-400 cycle and response times
19.2 Calculating the cycle time
S7-400H
358 System Manual, 03/2012, A5E00267695-11
19.2 Calculating the cycle time
Extending the cycle time
The cycle time of a user program is extended by the factors outlined below:
● Time-based interrupt processing
● Hardware interrupt processing (see also section Interrupt response time (Page 379))
● Diag
nostics and error p
rocessing (see also section Example of calculation of the interrupt
response time (Page 381))
● Comm
unication via MPI or the integrate
d PROFINET interface and CPs connected by
means of the communication bus
(e.g.: Ethernet, Profibus, DP) as a factor in communication load
● Special functions such as operator control and monitoring of tags
or the block status
● Transfer and deletion of blocks, compressing of the user program memory
● Runtime of signals using the synchronization cable
Influencing factors
The table below shows the factors influencing the cycle time.
Table 19- 2 Factors influencing cycle time
Factors Remark
Transfer time for the process
output image (POI) and process
input image (PII)
See tables from 19-3 onwards
User program execution time This value is calculated based on the execution times of the
various statements (see the
S7-400 statement list
).
Operating system execution time
at the cycle control point
See Table 19-7
Extension of cycle time due to
communication load
You configure the maximum permitted communication load on
the cycle as a percentage in STEP 7 (
Programming with STEP 7
manual). See section Communication load (Page 366).
Load on cycle times due to
interrupts
Interrupt requests can always stop user program execution. See
Table 19-8
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