Siemens CPU 410-5H Process Automation - Calculating the Cycle Time

Supplementary information
16.15 Cycle and response times of the CPU 410-5H
CPU 410-5H Process Automation/CPU 410 SMART
274 System Manual, 10/2013, A5E32631667-AA
16.15.2
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 288))
● Diagnostics and error processing (see also Chapter Example of calculation of the
interrupt response time (Page 290))
● 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 16- 10 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
(Manual Programming with
STEP 7 ). See Chapter Communication load (Page 277).
Load on cycle times due to
interrupts
Interrupt requests can always stop user program execution. See
Table 19-8
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.