Calculating The Cycle Time - Siemens SIMATIC CPU 410 System Manual

18.16.2

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 Chapter Interrupt response time (Page 373))
● Diagnostics and error processing (see also Chapter Example of calculation of the
interrupt response time (Page 375))
● Communication via the integrated PROFINET IO 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 monitoring and modifying variables
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 18- 10 Factors influencing cycle time
Factors
Transfer time for the process
output image (POI) and process
input image (PII)
User program execution time
Operating system execution time
at the cycle control point
Extension of cycle time due to
communication load
Load on cycle times due to inter-
rupts
Process image update
The table below shows the time a CPU requires to update the process image (process
image transfer time). The specified times only represent "ideal values", and may be
extended accordingly by any interrupts or communication of the CPU.
Calculation of the transfer time for process image update:
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC
18.16 CPU 410 cycle and reaction times
Remark
See tables from 19-3 onwards
This value is calculated based on the execution times of the vari-
S7-400 statement list
ous statements (see the
See Table 19-7
You configure the maximum permitted communication load on
the cycle as a percentage in STEP 7 (Manual
STEP 7
). See Chapter Cycle load due to communication
(Page 362).
Interrupt requests can always stop user program execution. See
Table 19-8
Supplementary information
).
Programming with
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