PLC Programming Language

1. Ladder diagram (LD)

• Ladder diagram is a graphical programming language derived from the circuit diagram.
• The ladder diagram contains contact rails A to the left side and the contact rails B to right of the diagram.
• These contact rails A & B are connected to switching elements (normally open/normally closed contacts) via current paths and coil elements.

Ladder Diagram

2. Function block diagram (FBD)

• In the function block diagram, the functions and function blocks are represented graphically and interconnected into networks. 
• The function block diagram understand from the logic diagram for the design of electronic circuits.
  

  

  Function Block Diagram

3. Instruction list (IL)

• Instruction list is a textual assembler type language.
• Instruction list is use an operator and an operand.
• The ladder diagram, function block diagram and instruction list languages are used in PLC Programming.

  

  Instruction List Diagram

4. Structured text (ST)

• Structured text is high-level language based on Pascal, which consists  of expressions and instructions.
• Instructions can be defined in the main as IF...THEN...ELSE etc., repetition instructions such as FOR, WHILE etc. and function block invocations.
  
  
  

  

  Structured Text Diagram

5. Sequential function chart (SFC)

• The sequential function chart is a language resource for the structuring of sequence-oriented control programs.
• The elements of the sequential function chart are steps, transitions, alternative and parallel branching.

  

  Sequential Function Chart Diagram