Calculating The Cycle Time - Siemens SIMATIC S7-400H System Manual

S7-400 cycle and response times

19.2 Calculating the cycle time

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))
● Diagnostics and error processing (see also section Example of calculation of the interrupt
● Communication via MPI or the integrated PROFINET interface and CPs connected by
● Special functions such as operator control and monitoring of tags
● 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
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
interrupts
358
response time (Page 381))
means of the communication bus
(e.g.: Ethernet, Profibus, DP) as a factor in communication load
or the block status
Factors influencing cycle time
Remark
See tables from 19-3 onwards
This value is calculated based on the execution times of the
various statements (see the
See Table 19-7
You configure the maximum permitted communication load on
the cycle as a percentage in STEP 7 (
manual). See section Communication load (Page 366).
Interrupt requests can always stop user program execution. See
Table 19-8
S7-400 statement list
).
Programming with STEP 7
System Manual, 03/2012, A5E00267695-11
S7-400H