How Cycle And Reaction Times Are Calculated; Longest Reaction Time; Example Of Calculating The Reaction Time - Siemens SIMATIC S7-400 Reference Manual

Cycle and Reaction Times of the S7-400
3.6

How Cycle and Reaction Times Are Calculated

Cycle time
1. Using the Instruction List, determine the runtime of the user program.
2. Calculate and add the transfer time for the process image. You will find guide
values for this in Table 3-3.
3. Add to it the processing time at the scan cycle checkpoint. You will find guide
values for this in Table 3-6.
4. CPU 417-4H: Multiply the calculated value by the factor in Table 3-5.
The result you achieve is the cycle time.
Increasing the Cycle Time with Communication and Interrupts
5. Multiply the result by the following factor:
6. Using the Instruction List, calculate the runtime of the program sections that
hardware interrupts. Add to it the relevant value in Table 3-7.
Multiply this value by the factor from step 4.
Add this value to the theoretical cycle time as often as the interrupt is triggered
or is expected to be triggered during the cycle time.
The result you obtain is approximately the actual cycle time. Make a note of the
result.
Table 3-9

Example of Calculating the Reaction Time

Shortest Reaction Time
7. Then, calculate the delays in the
inputs and outputs and, if applicable,
the DP cycle times on the PROFIBUS
DP network.
8. The result you obtain is the shortest
reaction time.
3-18
100 - "configured communication load in %"
100

Longest Reaction Time

7. Multiply the actual cycle time by a
factor of 2.
8. Then, calculate the delays in the
inputs and outputs and the DP cycle
times on the PROFIBUS DP network.
9. The result you obtain is the longest
reaction time.
Automation System S7-400 CPU Specifications
A5E00165965-01