Siemens Simatic S7 Series System Manual page 88

Programming concepts
5.2 Elements of the user program
● Interrupt routines are optional elements of your program that react to specific interrupt
events. You design an interrupt routine to handle a pre-defined interrupt event. Whenever
the specified event occurs, the CPU executes the interrupt routine.
The interrupt routines are not called by your main program. You associate an interrupt
routine with an interrupt event, and the CPU executes the instructions in the interrupt
routine only on each occurrence of the interrupt event.
Note
Because it is not possible to predict when the CPU might generate an interrupt, it is
desirable to limit the number of variables that are used both by the interrupt routine and
elsewhere in the program.
Use the local variable table of the interrupt routine to ensure that your interrupt routine
uses only the temporary memory and does not overwrite data used somewhere else in
your program.
There are a number of programming techniques you can use to ensure that data is
correctly shared between your main program and the interrupt routines. Refer to the
descriptions of the Interrupt instructions (Page 282).
● Other blocks contain information for the CPU. You can choose to download these blocks
when you download your program:
– System Block: The system block allows you to configure different hardware options for
– Data Block: The DB stores the initial values for different variables (V memory) used by
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the CPU.
your program.
System Manual, 09/2015, A5E03822230-AC
S7-200 SMART