Extension Of Cycle Time Due To Communication Load - Siemens Simatic S7-1500 Function Manual

Cyclic program execution
3.2 Cycle time
3.2.2.3

Extension of cycle time due to communication load

Impact of communication on the cycle time
In the sequence model of the CPU, communication tasks are processed with priority 15. All
program parts with priority > 15 (e.g. for Motion Control functions) are unaffected by
communication.
Configured communication load
The CPU operating system provides the maximum specified percentage of total CPU
processing power for communication tasks. The communication load is preset in STEP 7 at
50%, for example, for the CPUs of the S7 series. If the processing power is not needed for
communication, then the processing power is available to the operating system and the user
program.
Communication is allocated the requisite computing time in 1 ms increments, with priority 15.
At 50% communication load, 500 μs of each 1 millisecond are used for communication.
The following formula may be used to estimate the extension of the cycle time by
communication.
Figure 3-5
With a complete use of the communication load of 50% (default), the following value results:
Figure 3-6
The actual cycle time is up to twice as long as the cycle time without communication when
you use the default communication load.
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Formula: Impact of communication load
Extension of cycle time due to communication load
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD