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IEC 61131
The IEC 61131 Standard was developed with the input of vendors, end-users and academics, 

IEC 1131 consists of five main parts:

  1. General information
  2. Equipment and test requirements
  3. PLC programming languages
  4. User guidelines
  5. Communications
The third part IEC 61131-3 is the international standard for programmable controller programming languages. This standard for programmable controller languages specifies the syntax, semantics and display of the PLC programming languages:
  • Ladder diagram (LD)
  • Sequential Function Charts (SFC)
  • Function Block Diagram (FBD)
  • Structured Text (ST)
  • Instruction List (IL)
One of the primary benefits of the standard is that it allows multiple languages to be used within the same programmable controller. This allows the program developer to select the language best suited to each particular task. Via decomposition into logical elements, modularization and modern software techniques, each program is structured, increasing its re-usability, reducing errors and increasing programming and user efficiency .