Siemens SIMATIC S7-1500/ET 200MP System Manual page 213

Basics of program execution
9.2 Asynchronous instructions
Parallel processing of asynchronous instruction jobs
A CPU can process several asynchronous instruction jobs in parallel. The CPU processes the
jobs in parallel under the following conditions:
• Jobs for an asynchronous instruction are started while other jobs for that instruction are
still running.
• The maximum number of simultaneously running jobs for the instruction is not exceeded.
The figure below shows the parallel processing of two jobs of the WRREC instruction. The two
instructions are executed simultaneously for a certain duration.
Figure 9-2
Note
Dependencies between asynchronous instructions
The call order in the user program may differ from the order of execution of the
asynchronous instructions. This may lead to problems with dependencies between
asynchronous instructions.
Solution: To ensure the correct chronological execution, use the status outputs of the
asynchronous instructions in a sequencer. The next asynchronous instruction should only
when an asynchronous instruction is completed, and this is acknowledged via the parameter
DONE.
Example: With the recipe phases RecipeImport and RecipeExport you need a CSV file for the
recipe data. If you use the same CSV file for import and export, then the two asynchronous
instructions are interdependent. In a sequencer, link the status of the DONE parameter of the
RecipeImport instruction in the transition to the next step where the RecipeExport is
executed. The link thus ensures the correct execution.
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Parallel processing of the asynchronous instruction WRREC
Automation system
System Manual, 01/2023, A5E03461182-AK