A PLC (Programmer Logic Controller) is a programmable logic controller designed to execute automation processes in industry. It consists of an operating system (wonderware intouch) and a programming environment that can support one or more languages. These devices have been used for process automation since 1970. Since then their technology has been improving and today they offer great benefits for the industry. In this article we will explain the keys to programming in PLC.

Unlike a traditional computer, PLCs or programmable logic controllers do not have a keyboard, mouse, hard drive, or monitor. However, it is still a computer, with its hardware and software. The main difference that we find between a PLC and a normal PC is that the PLC receives signals through various input channels connected to sensors installed in the machine or process that they control. In the same way, it has output channels to transmit the orders to the machines and activate automatic processes. Hence a Programmable logic controller allows to control and monitor in real time the various industrial processes, presenting them in an HMI (human-machine interface) or in superior control networks. We can find PLC systemsin many different areas: dam control, substations, gas distribution, petrochemicals, production chains, etc…


Programming a PLC involves generating a set of instructions and commands that will cause the execution of a given task. We can say that a program is a predetermined response to all possible combinations of states of the information it receives. Programming in Programmable logic controller consists of various phases:

1 – Definition and analysis of the problem: First of all, we must identify what is the need that we want to solve through the programmable controller. What results should the system provide us? What data or information do we need to be able to determine the response of the machine?

2 – Definition of the automation architecture: We will define the hardware of the controller. Once we know what information or processes we need to monitor, we will configure the inputs of the controller so that it can receive the data that is collected through the sensors. Each PPLC is assigned a fatek plc programming cable specificially.

3 – Algorithm design: An algorithm consists of a sequence of steps required to execute a task. Thus, the method for decision making will be designed.

4 – Code programming: With all the processes defined, we will write the orders that will allow us to communicate with the machine. Programming languages ​​are used for this.

5 – Program debugging, testing and verification: The last phase involves a series of tasks aimed at verifying the correct operation of the program. Possible communication errors are detected and the corrections are made to guarantee optimal results of the automation system.


As PLC programming languages are made up of a series of symbols, characters and rules of use that were designed to be able to establish communication between users and machines. It is the code through which we are able to create a program with instructions to control the operation of any process or industrial machine. Currently, the international standard IEC 6131 defines the main programming languages ​​in Programmable logic controller:

1 – IL (Instruction List): It is a text language and it is the oldest programming language. In fact, it is the basis of all other languages ​​and was used when computers did not have graphic capabilities. IL is a low-level language and is reminiscent of assembly language. In this language all programs can be translated into a list of instructions. Program control is achieved through “jumps” and function calls.

2 – LD (Ladder): It is a graphic language and is the evolution of the IL language. Ladder language is also known as Ladder Diagram, since its structure is reminiscent of a ladder: it is made up of two vertical levels (feeding) and two horizontal levels. So the instructions are placed on the left side and outputs on the right side. The PLC processor will interpret the sides from bottom to top and from left to right.

3 – FBD (Function Block Diagram): Hence it is a graphic language that defines the function between the input and output variables. Logic symbol blocks are used in this language.

4 – ST (Structured Text): It is a graphical language that defines the function between the input and output variables. Remember the programming language C and Pascal. It consists of a series of instructions that can be executed conditionally. Checkout now to: open EML File in Outlook


Communication between two or more programmable logic controllers is possible through a special connection, built on the basis of rules, which allow the transfer of data or information between each of these. Hence these types of rules are known as “communication protocol”. So the best known communication protocols between PLC’s are: Profibus, Fieldbus, Modbus, Devicenet or Interbuss.

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