Function block language

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The function block language (abbreviation FBS / C +) is one of the five languages ​​defined in EN 61131-3 ( IEC 61131-3) for programming programmable logic controllers (PLC). It is often also called a function plan ( FBD abbreviation ) (especially with Siemens Step7 ). The graphically oriented programming language uses the logic symbols of Boolean algebra in its representation . It is particularly suitable for logic controls.

Its CAD functionalities allow functions and function blocks and their variables to be easily positioned and connected.

This also includes the FBD (Function Block Diagram / freely translated: "Function block diagram"). While the FBD “only includes the words and their meaning”, the FBD is responsible for the “visualization” and “function”. The FBD is used to write PLC programs.

An FBD program consists of the following graphic elements:

  • Connections and lines
  • Variables and constants
  • Functions and function blocks

The signal flow of an FBD program runs from left to right. The processing sequence of the blocks can be determined individually.

Example: Add 100 to VALUE1, limit the result to ± 10000 and write in VALUE2:

Simple FBD example

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