Siemens CPU 31 Series - Communication Load

Cycle and reaction times
5.2 Cycle time
CPU 31xC and CPU 31x, Technical Data
5-8 Manual, 01/2006 Edition, A5E00105475-06
Block processing times may fluctuate
Fluctuation of the block processing time (e.g. OB 1) may also be a factor causing cycle time
fluctuation, due to:
• conditional instructions,
• conditional block calls,
• different program paths,
• loops etc.
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.
5.2.4 Communication load
Configured communication load for PG/OP communication, S7 communication and PROFINET 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 %)
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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.