Cycle and response times
7.4 Calculating method for calculating the cycle/response time
7.3.4 Reducing the response time with direct I/O access
Reducing the Response Time
You can reach faster response times with direct access to the I/O in your user program, e.g.
with
• L PIB or
• T PQW
you can partially avoid the response times described above.
Note
You can also achieve fast response times by using process interrupts (see next chapter).
7.4 7.4 Calculating method for calculating the cycle/response time
Introduction
This section gives you an overview of how to calculate the cycle/response time.
Cycle time
1. Determine the user program runtime with the help of the instruction list.
2. Multiply the calculated value by the CPU-specific factor from the table
Extension of user
program p ocessing timer
.
3. Calculate and add the process image transfer time. Corresponding guide values are
found in table
Data for calculating process image transfer time
.
4. Add the processing time at the scan cycle checkpoint. Corresponding guide values are
found in the table
Operating system processing time at the scan cycle checkpoint
.
5. Include the extensions as a result of testing and commissioning functions. These values
are found in the table
Cycle time extension due to testing and commissioning functions.
The result you achieve is the
6.
cycle time
.
Extension of the cycle time as a result of interrupts and communication load
100 / (100 - configured communication load in %)
1. Multiply the cycle time by the factor as in the formula above.
2. Using the Instruction List, calculate the runtime of the program sections that hardware
interrupts. Add the corresponding value from section
Calculating the cycle time
, table
Cycle time extension by interrupt nesting.
S7-300 CPU Data: CPU 315T-2 DP
7-14 Manual, 12/2005, A5E00427933-02
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