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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Variable Declarations Variable Types All variables srandard within a project must be declared, either locally to a POU or globally to the project. These function blocks can be written in any of the five languages, including the Function Block Diagram language again.

The standare name can be used in other POUs with no conflict within the project. Its purpose is to generate a Boolean pulse the coil “Output” at regular intervals when started by a Boolean variable the relay “Run” going high, and it can be stopped by another Boolean variable the relay “Reset” going high: A function standad program, for example, can incorporate ladder diagram logic in it.

If this algorithm were to be written in Structured Text, it would be: This declaration would occur in the “System Resource” section of the project.

Users can also develop their own libraries, which can include calls to the IEC standard library and any applicable manufacturers’ libraries. Instruction List is most popular for relatively simple, yet frequently used, algorithms. Any use of a Function Block is referred to as an “instance” of that block.


Program Organization Units POUs Functions Functions are pre-programmed calculations that accept numerous inputs, but return only one output. Using Structured text, the code above is written as: Description of the fundamental concepts of IEC These include cold and warm program starts, floating point errors, and stack overflows. If shown as a Function Block, it looks like this: Assembler language is relatively tedious to program, but is supposedly faster to execute.

IEC-1131 – The First Universal Process Control Language

The manufacturers who support this standard are free to use their own on-line interface software, and future developments will allow more powerful stnadard capabilities between controllers of different manufacturers.

The general construct of a control algorithm includes the use of “tasks”, each of which sgandard have one or more Program POUs. A Function, when used, does not consume additional memory. This allows graphical representation of logic in a form easily understood by electrical technicians and engineers alike.

IEC allows multiple tasks, and these can be assigned priorities from 0 to 31 0 being highest. Each instance must be given a name that is unique to the POU in which the block resides.

Function Blocks are pre-programmed calculations that accept numerous inputs, and can return several outputs. Regardless of the type of POU or Language used, all variables must be isc.


What distinguishes a Function Block from a Function is that each instance contains a unique set of values that are retained with every execution of the instance.

IEC – The First Universal Process Control Language

IEC is the first international standard for process control software. Any controller that is IEC compliant supports these as a “firmware” library, that is, the code for these is standaard into a prom or flash ram on the device. Once variables have been declared globally, they can then be used in any POU by being re-declared as “External”.

The standard library standwrd IEC consists mostly of Functions. I ntroduction IEC is the first international standard for process control software. Also, arrays can be created that are combinations of structures. Users 131-3 create programs in any combination of the five languages, and can develop code as POUs that are re-usable within a project, and can be stored as libraries for use in other projects.

Inputs and outputs between the blocks are wired graphically using a mouse. Notice that Input and Output variables can be assigned initial values.

Tasks are the devices that execute Program POUs.

System tasks are triggered to execute once on specific events within the running program.