MULTIPROG: One hundred percent conformity with IEC 61131-3

The standard IEC 61131 has been established to standardize the multiple languages, sets of instructions and different concepts existing in the field of automation systems. The great variety of PLC concepts has led to an incompatibility between the different PLC platforms and manufacturers. The result was a great effort to be made for training, hard- and software investments.

IEC 61131 standardizes the programming languages, the interfaces between PLC and programming system, the sets of instructions and the handling and structuring of projects. The advantage of using IEC 61131 conform PLCs and programming systems is a portability of all platforms and the use of same concepts reducing costs for automation systems.

What is the use of the IEC 61131-3 standard?

The main changes that have come with IEC 61131-3 are:

• The IEC structure model defines the structure of the program code divided into clearly structured units, so called POUs (Program Organization Units). Each POU consists of a code part and a variables declaration part. POUs of the types program, function and function block (FB) are available. Function and FB POUs can be reused within the same project or when using libraries also in other projects.
• Instead of direct addressing of inputs, outputs and flags, variables are used according to IEC 61131. Similar to higher programming languages, the variables in the project must be declared. Global and local data can be differentiated. Furthermore, there is a distinction between symbolic, directly represented and addressed variables. Retentive variables can be declared, whose values are retained even if the power supply is switched off or fails. Variables can be initialized with an initial value.
• Declaration of data types is possible. Data types determine the format, size, possible value range and possible initial value of variables. The IEC defines a range of elementary data types (BOOL, BYTE, INT, WORD, DWORD, REAL, and many others). Furthermore, depending on the used control, user-defined data types like arrays and structures are possible.
• Programming means symbolic programming.
• The IEC describes five programming languages, defines their language elements as well as their syntax.
  

 [IEC programming languages]
 [additionally: Machine sequential function chart language]