IEC is a standard for programming languages used in programmable . When programming a PLC according to IEC , three so called pro-. PLC standard programming languages: IEC Abstract: Today, if programmable controllers from more than one vendor are used, more than one method of. IEC IEC SC65A(Sec)49, PC Languages. IEC 64A(Sec) IEC name change it took 20 years to make that standard C. Fantuzzi. 5.

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Advancing Automation eBook Series. Once variables have been declared globally, they can then be used in any POU by being re-declared as “External”.

Bristol Babcock is a leading supplier of measurement and control instruments and systems with offices throughout the world. For more information on Bristol Babcock, please visit their website at http: It is always referred to by its created name.

A task can be assigned a cyclic rate, can be event driven, or be triggered by specific system functions, such as startup. Inputs and outputs between the blocks are wired graphically using a mouse. This declaration would occur in the “System Resource” section of the project. When a Function or Function Block is created, it must have input and output terminals. Sequential Function charts allow complex algorithms to be executed using a series of “steps” and “transitions”.

IEC-1131 – The First Universal Process Control Language

This allows graphical representation of logic in a form easily understood by electrical technicians and engineers alike. All variables used within a project must be declared, either locally to a POU or globally to the project. The standard library of IEC consists mostly of Functions. Any controller that is IEC compliant supports these as a “firmware” library, that is, the code for these is pre-written into a prom or flash ram on the device.


Also, arrays can be created that are combinations of structures. Under some circumstances, a POU can have a combination of languages.

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This article was written and provided by Bristol Babcock. Instruction List is most popular for relatively simple, yet frequently used, algorithms. All user-declared POUs, regardless of type, can be written in any of the five languages.

System tasks are triggered to execute once on specific events within the running program. Users can also develop their own libraries, which can include calls to the IEC standard library and any applicable manufacturers’ libraries. Users can create programs in any combination of the five languages, and can develop code as POUs eic are re-usable within a project, and can be stored as libraries for use in other projects.

IEC – The First Universal Process Control Language

Also actions can be directed to continue running, run once, or terminate, instead of running continuously. The IEC Standard includes a library of pre-programmed functions and function blocks. Functions are pre-programmed calculations that accept numerous inputs, but return only one output. Additionally, manufacturers can supply libraries of their own functions.

If this algorithm were to be written in Structured Stadnard, it would be: Regardless of the type of POU or Language used, all variables must be declared. Notice that Input and Output variables can be assigned initial values.


If shown as Structured Text, it looks like this: Typically, these would also be firmware libraries. A function block program, for example, can incorporate ladder diagram logic in it. I ntroduction IEC is the first international standard for process control software.

Assembler language is relatively tedious to program, but is supposedly faster to execute. The manufacturers who support this standard are free to use their own on-line interface software, and future developments will allow more powerful communications capabilities between controllers of different manufacturers. Typically, a programmer would create his own algorithms as Functions or Function Blocks in Structured Text and use them as callable procedures in any of the five languages.

Additionally, user-declared variable types can be created that are “structures”, or combinations of several variable types.

IEC – Wikipedia

The control algorithm can include reusable entities referred to as “program organization units POUs ” which include Functions, Function Blocks, and Programs. Tasks are the devices stabdard execute Program POUs. These function blocks can be written in any of the five languages, including the Function Block Diagram language again. A brief example would be: Using Structured text, the code above is written as: