Basic IEC 61131-3 Function Blocks (safety-related and standard)
Function blocks are POUs with multiple input/output parameters and internal memory. The value a function block returns depends on the value of its internal memory. The abbreviation for function blocks is FB.
Due to the internal memory of each FB, it is necessary to store the related values to a different memory area each time the function block is used. This is done using instance names. The instance name has to be declared in the variable declaration of the POU where the function block is going to be used. You have to declare the instance name before you can insert it into the code body.
IEC 61131-3 describes basic function blocks. A subset of these function blocks are implemented in EcoStruxure Machine Expert - Safety.
NOTE:
Term definition: Standard = non-safety-related
The term "standard" always refers to non-safety-related items. Examples: a standard process data item is only read/written by a non-safety-related I/O device (i.e., a standard device). Standard variables/functions/FBs are non-safety-related data. The term "standard controller" designates the non-safety-related controller.
NOTE:
Standard function blocks are only allowed for programming standard program parts.
When programming a safety-related application a strict separation between safety-related and standard logic (networks) is required. Due to this, all IEC 61131-3-defined function blocks are also available as safety-related function blocks.
Representation
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In the Edit Wizard the standard function blocks are represented by the symbol |
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Safety-related function blocks are represented by the symbol |
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, in a code worksheet they appear in gray accordingly:
in the Edit Wizard and appear in red when inserted in a code worksheet: