Siemens SIMATIC CPU 410 System Manual page 372

Supplementary information
18.16 CPU 410 cycle and reaction times
Calculating the cycle time
The theoretical cycle time for the example is derived from the following times:
● As the CPU-specific factor is 1.2, the user program execution time is:
● Process image transfer time (4 x double-word access and 3 x word access)
● Operating system runtime at scan cycle checkpoint:
The total of the listed times is equivalent to the cycle time:
Cycle time = 12.0 ms + 0.184 ms + 0.31 ms = 12.494 ms.
Calculation of the actual cycle time
● Allowance for communication load:
● A time-of-day interrupt with a runtime of 0.5 ms is triggered every 100 ms.
The interrupt can be triggered a maximum of one time during a cycle:
Allowing for communication load:
● 20.823 ms + 1.65 ms = 22.473 ms.
Taking into account the time slices, the actual rounded up cycle time is 22.5 ms.
Calculating the longest response time
● Longest response time
● Delay of inputs and outputs
– The maximum input delay of the digital input module SM 421; DI 32×DC 24 V is 4.8
– The output delay of the digital output module SM 422; DO 16×DC 24 V/2A is
– An interference frequency suppression of 50 Hz was assigned for the analog input
– Analog output module SM 432; AO 8×13Bit was assigned for measuring range 0 ... 10
● All components are installed in the central controller, so DP cycle times can be ignored.
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approx. 12.0 ms
Process image: 9 µs + 7 ×25 µs = approx. 0.184 ms
approx. 0.31 ms
12.494 ms * 100 / (100–40) = 20.823 ms.
0.5 ms + 0.490 ms (from table 16-9) = 0.99 ms.
0.99 ms * 100 / (100–40) = 1.65 ms.
22.5 ms * 2 = 45 ms.
ms per channel
negligible.
module SM 431; AI 8×13Bit. The result is a conversion time of 25 ms per channel. As
8 channels are active, a cycle time of the analog input module of 200 ms results.
V. This results in a conversion time of 0.3 ms per channel. Since 8 channels are
active, the result is a cycle time of 2.4 ms. The transient time for a resistive load of 0.1
ms must be added to this. The result is an analog output response time of 2.5 ms.
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC