Siemens SIMATIC S7-400 Reference Manual page 106

Cycle and Reaction Times of the S7-400
Longest Reaction Time
The following figure shows you how the longest reaction time results.
SCC (OS)
PIQ
PII
User program
SCC (OS)
PIQ
PII
User program
SCC (OS)
PIQ
Figure 3-9 Longest Reaction Time
Calculation
The (longest) reaction time is made up as follows:
• 2 × process image transfer time of the inputs +
• 2 × process image transfer time of the outputs +
• 2 × operating system processing time +
• 2 × program processing time +
• 2 × runtime of the DP slave frame (including processing in the DP master) +
• Delay in the inputs and outputs
This is equivalent to the sum of twice the cycle time and the delay in the inputs and
outputs plus twice the DP cycle time.
3-16
Delay in the inputs
+ DP cycle time on the PROFIBUS-DP
While the PII is being read in, the status of the input
under review changes. The change of input signal is no
longer taken into account in the PII.
Here the change of input signal is taken into account
in the PII.
The change of input signal is processed here by the
user program.
The reaction of the user program to the change of input
signal is passed here to the outputs.
Delay in the outputs
+ DP cycle time on the PROFIBUS-DP
Automation System S7-400 CPU Specifications
A5E00165965-01