Cycle and Response Times of the S7-400
9.6 Calculating cycle and reaction times
S7-400 Automation System, CPU Specifications
9-18 Manual, 10/2006, 6ES7498-8AA04-8BA0
9.6 Calculating cycle and reaction times
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 approximate
values in the table "Portions of the process image transfer time".
3. Add to it the processing time at the scan cycle checkpoint. You will find approximate
values in the table "Portions of the process image transfer time".
The result you achieve is the cycle time.
Increasing the Cycle Time with Communication and Interrupts
1. The next step is to multiply the result by the following factor:
100
100 - "configured communication load in %"
2. Using the Instruction List, calculate the runtime of the program sections that hardware
interrupts. Add to it the relevant value from the table "Increase in cycle time by nesting
interrupts".
Multiply this value by the factor from step 1.
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 9-7 Example of Calculating the Response Time
Shortest response time Longest response time
6. Multiply the actual cycle time by a factor of 2. 6. Then, calculate the delays in the inputs and
outputs and, if applicable, the DP cycle times on
the PROFIBUS DP network.
7. Then, calculate the delays in the inputs and
outputs and the DP cycle times on the
PROFIBUS DP network.
7. The result you obtain is the shortest response
time.
8. The result you obtain is the longest response
time.
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