A Programmable Logic Controller – PLC, also known as programmable controller, is the name given to a type of computer commonly used in commercial and industrial. The most commonly utilized programming languages in PLCs:

1. Ladder Logic (LD)
2. Structured Text (ST)
3. Function Block Diagram (FBD)
4. Instruction List (IL)
5. Sequential Function Chart (SFC)

Ladder Logic (LD) - Ladder Logic, also known as Ladder Diagram, is a graphical PLC programming language based on relay logic’s circuit diagrams. Ladder Logic consists of two parallel bars connected by a series of rungs, resembling a ladder in appearance (hence, the name). There are contacts and coils on these rungs, which symbolize inputs (such as a sensor value) and outputs (like a motor run command) respectively. The most established and often utilized programming language in PLC is ladder logic. It based its graphical representation of the logic processes on electrical ladder diagrams utilized in relay-based control systems.

Structured Text (ST) - Structured Text (ST) is a high-level PLC programming language. It’s a textual language, with syntax comparable to C or C++, so those who have studied these types of computer programming languages will have an easier time with it. In ST, statements (such as IF, for example) are used to perform functions. High-level text-based programming languages like structured text resemble traditional languages like Pascal or C. It is suitable for performing mathematical computations and manipulating data, and it enables more complicated programming.

Function Block Diagram (FBD) - Function Block Diagram (FBD) is another popular graphical PLC programming language. It consists of various kinds of blocks that have inputs and outputs. Devices connected to the PLC can be linked to an input, and variables can be sent to an output. Additionally, blocks connect to each other — the output of one block can feed into another block’s input. These blocks are what define the functions of a system. By implementing several function blocks together, users of the graphical programming language FBD can construct complex functions. It is helpful for illustrating complex control procedures and has a visual resemblance to electrical schematics.

Instruction List (IL) - Instruction List (IL) is a low-level textual PLC programming language. Instruction List was deprecated in the IEC’s standard, which means it’s doubtful that new PLCs will be programmed with it. Since some current PLCs may still use IL, however, it’s helpful to know what it’s all about A text-based, low-level programming language called Instruction List uses mnemonic codes for representing specific instructions. Reading and writing it is more difficult, but it has its uses where memory minimization is important.

Sequential Function Chart (SFC) - Sequential Function Charts (SFC) is a graphical PLC programming language based on GRAFCET, and resembles computer science algorithm flowcharts. SFC consists of steps and transitions. Steps are the actions to be performed, and transitions are the logic conditions that need to be met before moving on to the next step. Due to the nature of this architecture, SFC controls a program’s operational flow. In order to make the control flow more understandable, SFC is the graphical programming language that enables to break down complex control processes into a series of logical phases or states.