Beginning 1990 the International Electrotechnical Commission (IEC) established the Standard IEC 1131. At the end of 1990 it was renamed (IEC 61131). This standard unifies the PLC programming, which was dependent on the manufacturer before. Part 3 (IEC 61131-3) of this international standard contains the specification of the programming languages. As a German standard DIN IEC 61131-3 it also substitutes the standards DIN 19239, DIN 40719T6 and the VDI-guideline VDI 2880 sheet 4.
There are 5 programming languages of the IEC 61131-3:
The well-tried languages from the 'classic' PLC programs
- Instruction List (IL)
- Ladder diagram (LAD)
- Function block language (FBL)
were integrated in the standard, as well as programming languages made for current requirements:
- sequential function chart (SFC)
- Structured text (ST)
Partly the different languages can be combined. They can also be mixed in almost any combination. Consequently, in the framework of the project e. g. an ST-block can be called from the program step of the SFC.
A big advantage of programming languages according to IEC 61131-3 results from the application of different PLC systems. Re-usability and interchangeability of programs facilitates the port between different systems. The user has the advantage of a unified language and program structure. This brings advantages due to savings in the training of the application programmers. Due to the standardization and certification programming systems can be compared and evaluated.
Note: The
CFC-editor of the Drive PLC Developer Studio (
DDS) is not standardized in the IEC 61131-3 and is an additional programming language in the DDS.
