Special Consideration When Profinet Io Communication Is Configured On The 2Nd Profinet Interface (X2) - Siemens Simatic S7-1500 Function Manual

Cyclic program execution
3.2 Cycle time
Effect on the actual cycle time
Communication is only one cause of extension of the cycle time. All configured events that
extend the cycle time (e.g. hardware interrupts) mean that more asynchronous events can
occur within a cycle. These asynchronous events further extend the cyclic program. The
extension depends on the number of events that occur and are processed in the cycle.
Note
Checking parameter changes
• Check the effects of a value change on the "Cycle load due to communication" parameter
during system operation. You can use the "RT_INFO" instruction to determine which
portions of runtime are used for communication and the user program.
• Take the communication load into consideration when setting the maximum cycle time to
prevent time errors (for example, exceeding the cycle time within a cycle) from occurring.
Tips
Whenever possible, use the default setting for the configured communication load.
If you reduce the value of the communication load, keep in mind that communication tasks
are interrupted by higher-priority OBs. This means it will also take longer to process the
communication.
3.2.2.4 Special consideration when PROFINET IO communication is configured on the 2nd
PROFINET interface (X2)
If you configure the PROFINET IO communication at the 2nd PROFINET interface (X2) on
the following CPUs as of firmware version 2.0, an additional system load occurs:
● CPU 1515(F)-2 PN
● CPU 1515T(F)-2 PN
● CPU 1516(F)-3 PN/DP
● CPU 1516(F)pro-2 PN
● CPU 1516T(F)-3 PN/DP
This additional system load has priority 26 and extends the runtime of the program. The
execution of synchronous cycle interrupts or hardware interrupts, for example, can be
delayed as a result.
The additional system load depends on:
● Communication traffic at the 2nd PROFINET interface (X2)
The communication traffic at the interface in frames per second causes communication
load as well as system load. You cannot limit the communication traffic using the
"Communication load" parameter.
● Number of IO devices which the CPU at the 2nd PROFINET interface (X2) updates within
a millisecond
You determine the additional system load with the "RT_INFO" (read RUNTIME statistics)
instruction at the Mode parameter with mode 10 or mode 20.
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Cycle and response times
Function Manual, 10/2018, A5E03461504-AD