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Supplementary information
16.15 Cycle and response times of the CPU 410-5H
The diagnostic interrupt response time of the signal modules is the time from detection of a
diagnostic event by the signal module to the triggering of the diagnostic interrupt by the
signal module. This short time can be neglected.
Hardware interrupt processing
Hardware interrupt processing begins when the hardware interrupt OB 4x is called. Higher-
priority interrupts stop hardware interrupt processing. Direct access to I/O modules is
executed during the execution time of the operation. After the hardware interrupt has been
processed, the system either resumes cyclic program processing, or calls and processes
interrupt OBs of the same or lower priority.
16.15.8
Example of calculation of the interrupt response time
Elements of the interrupt response time
As a reminder: The hardware interrupt response time is made up of the following:
● Hardware interrupt response time of the CPU
● Hardware interrupt response time of the signal module
● 2 × DP cycle time on PROFIBUS DP
Example
You have installed a CPU 410-5H and four digital modules in the central controller. One
digital input module is the SM 421; DI 16×UC 24/60 V; with hardware and diagnostic
interrupts. You have enabled only the hardware interrupt in your CPU and SM parameter
assignment. You decided not to use time-driven processing, diagnostics or error handling.
You have assigned an input delay of 0.5 ms for the digital input modules. No activities are
required at the scan cycle checkpoint. You have set the communication load of the cycle as
20%.
Calculation
In this example, the hardware interrupt response time is based on following time factors:
● Process interrupt response time of CPU 410-5H: Approx. 0.3 ms (mean value in
redundant operation)
● Extension due to communication according to the description in Chapter Interrupt
response time (Page 288):
100 µs + 1000 µs × 20% = 300 µs = 0.3 ms
290
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
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