Siemens S7-300 appendix Communication load, Maximum cycle time, Example 20 % communication load

Cycle and reaction times 5.2 Cycle time

Maximum cycle time

In STEP 7 you can modify the default maximum cycle time. OB80 is called on when this time expires. In this block you can specify the CPUs response to this timeout error. The CPU switches to STOP mode if OB80 does not exist in its memory.

5.2.4Communication load

Configured communication load for PG/OP communication, S7 communication and CBA

The CPU operating system continuously provides a specified percentage of total CPU processing performance (time-sharing technology) for communication tasks. Processing performance not required for communication is made available to other processes. In HW Config, you can specify a communication load value between 5% and 50%. Default value is 20%.

You can use the following formula for calculating the cycle time extension factor:

100 / (100 – configured communication load in %)

Time slice (1 ms)

Interruption

of user program

Share can be configured between 5 % and 50 %

Example: 20 % communication load

In your hardware configuration, you have specified a communication load of 20 %. The calculated cycle time is 10 ms. Using the above formula, the cycle time is extended by the factor 1.25.

Example: 50 % communication load

In your hardware configuration, you have specified a communication load of 50%. The calculated cycle time is 10 ms. Using the above formula, the cycle time is extended by the factor 2.

CPU 31xC and CPU 31x, Technical data	5-9
Manual, Edition 08/2004, A5E00105475-05