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A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines. Inputs and outputs of the blocks are wired together with connection lines or links. Single lines may be used to connect two logical points of the diagram: An input variable and an input of a block; An output of a block ...
As programming terminals evolved, because ladder logic was a familiar format used for electro-mechanical control panels, it became more commonly used. Newer formats, such as state logic, [18] function block diagrams, and structured text exist. Ladder logic remains popular because PLCs solve the logic in a predictable and repeating sequence, and ...
Part 3 of IEC 61131 deals with basic software architecture and programming languages of the control program within PLC. It defines three graphical and two textual programming language standards: Ladder diagram (LD), graphical; Function block diagram (FBD), graphical; Structured text (ST), textual
ST (structured text) is similar to programming in Pascal or C; LD (ladder diagram) enables programmers to virtually combine relay contacts and coils; FBD (function block diagram) enables users to rapidly program both Boolean and analog expressions; SFC (sequential function chart) is convenient for programming sequential processes and flows
Sequential function chart (SFC) is a visual programming language used for programmable logic controllers (PLCs). It is one of the five languages defined by IEC 61131-3 standard. The SFC standard is defined as Preparation of function charts for control systems , and was based on GRAFCET [ fr ] (itself based on binary Petri nets [ 1 ] [ 2 ] ).
As microprocessors have become more powerful, notations such as sequential function charts and function block diagrams can replace ladder logic for some limited applications. Some newer PLCs may have all or part of the programming carried out in a dialect that resembles BASIC , C , or other programming language with bindings appropriate for a ...
Many vendors whilst incorporating the full IEC 61131-3 requirements have additional vendor specific calls/function blocks to suit their hardware such as reading or writing to I/O. Siemens PLC instruction list language is known as "Statement List" or "STL" in English, and "Anweisungs-Liste" or "AWL" in German, Italian and Spanish.
Function blocks (FB) - contain frequently occurring and particularly complex program parts; Data blocks (DB) - for storing data required for processing the control program. Some S5 PLCs also have block types FX (Extended Function Blocks), and DX(Extended Data Blocks); these are not distinct block types, but rather are another set of available ...