How to Learn PLC Programming

PLC Programming: Step-by-Step Guide on How to PLC Program

Embarking on the journey of PLC programming can seem daunting; however, our guide simplifies the process. Whether you’re new to the field or looking to sharpen your skills, we provide the essentials on how to PLC program. Learn how to set up your environment, understand the core components, write your first program, and integrate it with industrial systems.

By the end of this article, you’ll not only understand PLC programming but be well on your way to implementing it. Let’s get started!

Key Takeaways

  • PLCs (Programmable Logic Controllers) are critical for industrial automation, with core components including the CPU, I/O modules, and power supply. They use proprietary software for programming, which optimizes system performance and maintenance.
  • Setting up a PLC programming environment involves selecting the right programming devices, which should have adequate specifications, and installing and configuring appropriate PLC programming software, adhering to system requirements.
  • Advancements in PLC programming encompass various advanced techniques like structured text and sequential function charts for complex logic, as well as simulation tools like PLCLogix for effective testing and debugging of the programs.

Discovering the Basics of PLC Systems

Industrial automation control system with PLC components

A PLC, short for Programmable Logic Controller, was developed in the late 1960s within the US automotive industry, with the primary aim to enhance the control of manufacturing processes. PLCs, or programmable logic controllers, were designed to replace relay-based circuits, streamline the process of altering operations, and enhance the dependability of the system. They are well-suited for various automation tasks and serve as the core of industrial automation.

PLC programs controlling machine operation are typically stored in battery-backed-up or non-volatile memory. This feature retains the programs even during power outages. This integration of computers into PLC programming began in the 1980s, signifying the shift towards modern PLC programming practices that involve input and output devices.

The Core Components: CPU, I/O Modules, and Power Supply

The core components of a PLC system are:

  • The CPU module, which is responsible for managing all processing and mathematical operations required for automation processes. It powers outputs based on inputs, manipulates memory locations, carries out arithmetic and logic operations, transfers data between the ladder logic and itself, and executes the application program.
  • The I/O modules, which provide the interface between the PLC and the external devices. They receive signals from sensors and send signals to actuators.
  • The power supply, which provides the necessary electrical power for the PLC system to function.

The I/O modules gather signals from various sensors, switches, or push buttons, and transmit this data to the CPU. The output modules then receive processed instructions from the CPU and initiate relevant control actions for devices such as:

  • relays
  • valves
  • motor starters
  • alarms
  • pumps

When selecting a power supply for a PLC system, consider a voltage range capable of sufficiently powering the CPU and the I/O modules.

Understanding PLC Programming Software Package

PLC programming software packages, such as Siemens, Allen Bradley, Mitsubishi, Schneider Electric, and Omron PLC, are integral to PLC programming. Utilizing a proprietary software package for PLC programming provided by the PLC manufacturer offers improved integration with the PLC hardware, optimized performance, access to manufacturer-specific features and support, facilitates easier upgrades and maintenance, lowers the total cost of ownership, and provides a unified control system for enhanced integration with other automation components.

For instance, Function Block Diagram (FBD) is a graphical language resembling a comprehensible, interconnected ‘wiring structure’. You can learn more about the different plc programming languages here.

Setting Up Your PLC Programming Environment

Setting up PLC programming environment

Having familiarized ourselves with the basics of programmable logic controller systems and their programming software, it’s time to set up your PLC programming environment. This involves choosing the right programming device and installing and configuring the necessary software.

The most suitable devices for PLC programming are laptops with adequate memory, hard disk space, communication ports, durability, and a compatible operating system.

The procedure for installing PLC programming software on a specific device involves:

  1. Opening the programming software installed on your PC that comes with the PLC hardware.
  2. Selecting the hardware model of the PLC in the software and commencing programming.
  3. For optimal configuration of PLC programming software, start by installing the necessary software for your specific PLC system.
  4. Define the task and inputs/outputs within the software.
  5. Develop a logical sequence of operations.
  6. Configure all parameters and program the PLC hardware’s logic to ensure successful deployment.

Choosing the Right Programming Device

To be an effective PLC programmer, you need the right tools for the job. A vital component for PLC programming is a programming device, which could be a desktop console, specialized software on a personal computer, or a handheld programming device. The programming devices accessible for PLC programming comprise hand-held units, PCs, or desktop units.

Key considerations when selecting a PLC programming device include:

  • Application requirements
  • Scalability and flexibility
  • Programming languages and software
  • Communication capabilities
  • Power supply
  • Speed
  • CPU speed
  • Memory capacity

Installing and Configuring PLC Programming Software

Before installing PLC programming software, ensure your system meets the necessary specifications:

  • An Intel Core i3, i5, i7, AMD Ryzen 3, 5, 7 or equivalent processor
  • At least 4GB of RAM
  • 500 MB of available disk space
  • A Windows operating system

PLC programming software is mainly compatible with Windows operating systems, with limited support for macOS in certain software, typically tailored to specific PLC brands.

The procedural steps for installing PLC programming software involve:

  1. Initially installing the required programming software for the PLC system.
  2. Subsequently, connecting the PLC system to the computer and adhering to the installation instructions provided by the software.
  3. To achieve optimal performance when configuring PLC programming software, it is important to select the appropriate PLC platform for your specific requirements.
  4. Additionally, maintaining software programs through activities such as understanding, documenting, backing up, testing, updating, and monitoring them is crucial.
  5. Furthermore, refactoring or updating the PLC application can also contribute to enhancing its performance.

Configuring the workspace in PLC programming software generally entails:

  1. Accessing the ‘View’ menu
  2. Selecting ‘Workspace’
  3. Modifying the current configuration
  4. Making required adjustments

The process for functions such as adding function blocks to the library will vary based on the specific programming software being utilized.

Crafting Your First PLC Program

Creating first PLC program with ladder diagrams

With our PLC programming environment set up, we can get down to crafting our first PLC program. This involves using ladder diagrams and function blocks to establish control logic and perform complex operations.

The one-shot operation is a feature in PLC programming that generates a brief output pulse without maintaining its state within the program. It is commonly utilized in ladder diagrams to guarantee the execution of a command occurs only once during a cycle.

The OR operation in ladder logic produces a ‘1’ output when at least one of the inputs is a ‘1’. This feature enables the activation of a single output based on multiple conditions, offering flexibility in the design of control circuits.

XOR, also known as ‘Exclusive OR’, serves as comparators in PLC programming to generate an output signal when the two input signals satisfy specific conditions, enabling the implementation of decisions based on diverse inputs.

The Master-Slave operation in PLC programming serves to utilize master inputs to establish the entire program’s dependency on a single control condition, thereby enabling a means for global control within a program.

Establishing Control Logic with Ladder Diagrams

The ladder diagram in PLC programming serves as a visual depiction of control logic, incorporating symbols and elements like contacts, coils, and rungs. Its layout follows a left-to-right and top-to-bottom orientation, facilitating the flow of power through the rungs from left to right.

The Start and Stop buttons in a ladder diagram serve to regulate the operational state of a device or process. Activation of the start button energizes a run coil in the ladder logic program, enabling the device or process to commence. Conversely, pressing the stop button de-energizes the run coil, halting the device or process.

The AND condition in PLC programming refers to two inputs in series with each other, where both inputs must have continuity for the output to turn on. The XOR condition in PLC programming involves the execution of NOT, AND, and OR conditions in ladder logic programs. It allows only one input variable to control the output at a time.

When scanning a program for continuity of rungs, a PLC follows a top to bottom, left to right sequence to check continuity between the two rails for each scan. This ensures thorough checking of the rungs for proper continuity during the program scan.

Incorporating Function Blocks for Complex Operations

Function blocks are a fundamental aspect of PLC programming, representing a straightforward method where ‘Function blocks’ are accessible within the programming software. They play a crucial role in simplifying complex operations in PLC programming by minimizing redundant code and enabling dynamic code generation through input parameters. They offer a modular and reusable method of programming, thereby enhancing the management and maintenance of complex operations.

Function blocks in PLC programming simplify complex operations by visually representing specific functions or operations. They feature inputs and outputs that can be linked to devices and variables, streamlining the programming and control of intricate processes.

Instances of complex operations made simpler using function blocks include assignment blocks for assigning inputs to PLC memory and output blocks for connecting to external devices.

Advanced PLC Programming Techniques

Implementing structured text in PLC programming

As we venture further into PLC programming, it’s time to uncover some advanced techniques. This includes:

  • Structured text for scripting and data manipulation
  • Sequential function charts for process control
  • Sequential Flow Chart (SFC), which is a basic form of PLC programming language that primarily comprises decision logics
  • An instance of a task that can be executed using Sequential Function Chart (SFC) is a pick and drop operation that entails a single active set of instructions with exceptions.

When the logic is complex and cannot be converted into another language, SFC programming may result in excessively long charts. Other advanced PLC programming techniques include Structured Text and Function Block Diagrams.

Structured Text for Scripting and Data Manipulation

Structured Text is a widely utilized programming language that bears resemblance to high-level languages such as PASCAL, C, and C++. It is employed in PLC programming to construct intricate routines and sequences, featuring a syntax akin to that of conventional programming. This characteristic facilitates a smoother transition for programmers accustomed to these languages.

The benefits of using structured text in PLC programming include:

  • The elimination of the need for a PLC programming background
  • A seamless transition for individuals with a background in traditional programming languages
  • A more compact usage of space compared to ladder logic
  • The ability to create complex routines and flows more efficiently.

The challenges of utilizing structured text in PLC programming include:

  • Its less intuitive and visual nature in comparison to ladder logic
  • The need for a higher level of training and experience, especially for individuals not familiar with high-level programming languages
  • The intricacy of debugging structured text programs due to their text-based format.

An illustration of structured text in a PLC program could be represented by a line such as ‘Buzzer:=PushA OR ( PushB AND (NOT PushC) );’ This line showcases the utilization of Boolean logic to control a buzzer, which is activated based on the conditions of push buttons A, B, and C.

Sequential Function Charts for Process Control

Sequential function charts serve as visual depictions of the sequence of actions required for the operation of a PLC control system. They provide benefits including the easy organization of ladder or structured text, simplification of logic for sequential operations, and effective visualization of complex sequences.

Sequential Function Charts in PLC programming are constructed by representing states or steps as rectangular boxes connected by vertical lines. Each step has a corresponding output, and there are transition conditions between steps. Sequential Function Charts (SFC) is a graphical programming language that sets itself apart from ladder diagrams by executing each step in isolation and advancing to the next step only after completion.

Fine-Tuning and Debugging Your PLC Program

PLC program debugging and testing with simulation tools

After getting your PLC program up and running, the subsequent step involves fine-tuning and debugging for optimal performance. PLC simulation is a capability present in PLC programming software, which facilitates early testing and debugging in a project’s development phase. It functions by providing the programmer with a software simulator to test their code, running the PLC program, and monitoring the outcomes without the requirement of physical hardware or wiring.

PLCLogix is considered one of the top choices for testing and debugging PLC programs. It offers the following features:

  • Replicates the functionalities of widely utilized PLCs such as the Logix 500 and Logix 5000
  • Real-time compilation to address common programming errors, including syntax, logic, and communication issues
  • Debugging tools for effective troubleshooting
  • Ability to compare the PLC program with a master program
  • Diagnosing in standby mode

These simulation tools make testing and debugging PLC programs more efficient and effective.

Correctly configuring error messages in PLC programming is crucial as it establishes a standardized message system that facilitates understanding of issues across the system. This standardization is essential for efficient error handling and diagnostics, enabling quick identification and resolution of errors.

Simulation Tools for Testing

Commonly recommended simulation tools for PLC Programming include MATLAB, Simulink, and Model-Based Design for plant modeling and PLC simulation, as well as PLCLogix 500 for learning the fundamentals. A high-quality PLC Simulation tool should offer features including emulation of analog and discrete I/O, as well as access to logic elements such as timers, counters, and control bits.

Simulation tools play a crucial role in testing PLC programs. They:

  • Transform the computer into a virtual PLC
  • Provide the capability to design and assess the performance of the control system without exposing any risk to assets or the manufacturing process
  • Facilitate the creation and testing of control programs in advance of hardware availability
  • Allow for the exploration of ‘what-if’ scenarios, leading to time and cost savings.

Simulation tools for PLC have been effective in:

  • Identifying potential issues in the program through fault finding
  • Proactively identifying issues
  • Thorough testing and simulation before implementation
  • Preventing problems caused by code bugs.

Effective Error Handling and Diagnostics

Error handling in PLC programming encompasses the identification and management of errors and exceptions within ladder logic diagrams, with the aim of implementing suitable measures to rectify them. These measures may include:

  • Prompt and secure issue resolution
  • Disregarding errors
  • Recording errors
  • Notifying errors
  • Recovering from errors
  • Halting the program

Error handling significantly enhances program reliability by guaranteeing that the PLC functions as designed, thereby reducing the adverse effects of errors on system efficiency and safety.

Typical errors in PLC programming encompass erratic readings or unresponsive sensors, logic errors, and incorrect encodings. These can be diagnosed through techniques such as verifying the input devices for proper wiring, employing diagnostic tools, and utilizing a multimeter for systematic troubleshooting.

Recommended approaches for error handling and debugging in PLC programming involve utilizing troubleshooting tools to identify and resolve software issues, implementing logging and tracing to monitor program execution, and utilizing conditional statements, try-catch blocks, or error codes to effectively manage errors.

Optimizing Your PLC Code for Performance and Scalability

As we further explore PLC programming, we will now focus on optimizing our PLC code for improved performance and scalability. This involves implementing modular design principles and efficiently using memory and resources.

Modularity in PLC systems involves organizing code into separate functional units or modules, which brings benefits such as enhanced flexibility and scalability, simplified addition and integration of I/O devices, and easier system upgrades and maintenance.

To effectively implement modular design in PLC code, it is advisable to divide the PLC code into distinct modules, utilize descriptive and consistent naming conventions, provide thorough comments for improved comprehension, and employ error handling techniques to ensure dependability.

Optimizing memory usage in PLC programming can be accomplished through the following strategies:

  • Use subroutines and functions to eliminate repetitive code
  • Streamline logic to decrease complexity
  • Strive for shorter PLC cycle times to minimize memory consumption

To improve resource efficiency of PLC code, it is essential to:

  • Streamline, structure, and modularize code
  • Minimize unnecessary complexity
  • Conduct comprehensive testing and performance evaluation
  • Prioritize energy optimization when relevant

Modular Design Principles

Modular design in PLC programming provides several benefits, including:

  • Increased memory capacity
  • Ability to store a larger amount of information
  • Scalable and flexible approach to coding complex systems
  • Effortless expansion and adaptation of the system
  • Utilization of standardized programming languages
  • Creation of code that can undergo testing once, enhancing efficiency and quality.

Modular design in PLC programming enhances flexibility by improving performance, promoting reusability, and facilitating easy reconfiguration or replacement to accommodate evolving system requirements. Recommended modular design strategies for PLC programming include:

  • Implementing good grounding practices
  • Considering environmental concerns
  • Documenting electrical schematic and PLC logic
  • Using modular programming and function block diagrams
  • Utilizing a modular software framework
  • Implementing unit, equipment, and control modules.

The implementation of modular design in PLC programming software involves breaking down a large and complex project into smaller modules, each with a specific purpose and functionality. These modules can be called by other modules or the main program, making the code easier to understand, test, and debug.

Efficient Use of Memory and Resources

Recommended best practices for optimizing memory management in PLC programming include optimizing scan time and memory usage, measuring and monitoring memory usage, and structuring memory effectively.

PLC memory optimization improves program performance by employing data types that align with the size and range of data values, consolidating related data into efficient formats, and utilizing constants and literals in place of variables.

Data types play a crucial role in determining the efficiency and reliability of PLC programs by influencing memory usage. Data is classified into various different types of data that an object or variable can contain (or hold) in a program. In all programming languages, data types are very important: before we develop any program or software, data types must be assigned and applied properly to ensure an error-free program with the right outcomes.

For monitoring and assessing memory usage in PLC programs, one can employ methods such as measuring memory usage and trending it on the HMI for each PLC controller, or utilizing the CODESYS Memory Tools, which offer capabilities for displaying memory mapping for an application in CODESYS.

Integrating PLCs with Other Industrial Control Systems

Having covered the basics, let’s now delve into more complex aspects of PLC programming, starting with integrating PLCs with other industrial control systems. This involves using communication protocols, networking, and interfacing with human-machine interfaces (HMIs). PLCs employ a range of industrial network protocols such as Modbus or EtherNet/IP to establish communication with external devices and systems.

P2P communication in PLCs serves the purpose of enabling separate components of a complex process to maintain individual control, while also facilitating coordination between subsystems through the communication link.

Human-Machine Interfaces (HMIs) serve as an operator control panel for PLCs, providing a graphical user interface to automate control processes and facilitate digital interaction with the system.

Communication Protocols and Networking

The prevalent communication protocols utilized in PLCs include:

  • Ethernet/IP
  • Modbus
  • Profibus
  • Optomux
  • DF-1
  • Interbus
  • HostLink
  • Data Highway (DH+)

PLC communication protocols play a crucial role by providing a standard communication interface that facilitates seamless collaboration between different devices and systems. The functionality of networking within a PLC system encompasses the physical and logical arrangement of communication networks between PLCs in an industrial automation system, referred to as PLC network topology.

It is crucial to comprehend the available PLC network options and their optimal applications for the design of an efficient and adaptable control system.

Ethernet provides benefits such as:

  • Enhanced performance
  • Flexible topology
  • Simplified configuration
  • Other advantages

However, one of its primary drawbacks is its non-deterministic protocol nature, which does not ensure data delivery.

Modbus protocol functions as a means of transmitting data over serial lines between electronic devices. It follows a master/slave architecture, allowing a Modbus master to communicate with multiple Modbus slaves for data exchange. The master is responsible for sending read and write instructions to the slave’s internal memory registers, enabling configuration, monitoring, and control of the slave’s operations.

Interfacing with Human-Machine Interfaces (HMIs)

Human-Machine Interfaces (HMIs) play a crucial role in control systems, serving as the operator’s method of interacting with PLCs and replacing manually activated switches and dials. HMIs serve as user interfaces or dashboards that facilitate the connection between a person and a machine, system, or device in industrial control systems. They are capable of:

  • displaying data
  • tracking performance
  • controlling settings
  • performing other functions.

The process of interfacing a PLC with an HMI involves programming the PLC to communicate with the HMI using a serial or Ethernet connection. The HMI software acts as a window into the PLC memory. The integration of PLCs with HMIs offers operators improved visualization and touch controls, leading to enhanced user-friendliness and functionality of the system.

HMIs enhance user interaction and control in PLC systems by replacing manually activated switches, dials, and other controls with graphical representations of the control process and digital controls. This user-friendly interface allows operators to:

  • Monitor and control the PLC systems
  • Start and stop cycles
  • Adjust set points
  • Perform other necessary functions

The Future of PLC Programming in Industry 4.0

As we near the conclusion of our exploration of PLC programming, let’s take a glimpse into the future. In the era of Industry 4.0 and smart manufacturing, PLC programming is adapting by incorporating:

  • Big data analysis
  • Robotic automation
  • Cloud computing
  • Enabling operation in extreme environments
  • Remote functionality
  • Communication with sensors via the Industrial Internet of Things (IIoT)

Proximity detection serves as a safety feature in modern PLC systems, aiming to mitigate accidents and injuries caused by machinery. Safety PLCs comply with the Safety Integrity Level (SIL) standard, which specifies the level of risk reduction offered by a safety function. Safety-specific instructions in safety PLCs are designed to enable seamless interactions with emergency stops, light curtains, and other safety mechanisms.

Adapting to Smart Manufacturing Trends

The influence of Industry 4.0 on PLC programming is evident in the enhanced connectivity and data exchange made possible by connecting PLCs to other machines and the internet.

Moreover, the emergence of smart industrial control services (SICS) is introducing a new type of PLC, supporting distributed service-oriented control systems. These technological advancements in PLCs are driving innovation in manufacturing and industrial systems.

The significant trends in smart manufacturing that PLC programmers should be mindful of include:

  • The integration of digital technologies with industrial processes (Industry 4.0)
  • The utilization of open standards
  • Object-oriented programming
  • Functional programming
  • Visual programming
  • Model-based programming

Furthermore, smart factories are a top strategic technology trend, leading to the creation of new forms of efficiency and flexibility.

The role and responsibilities of a PLC programmer are evolving in the context of smart manufacturing. This includes:

  • Integrating and maintaining new robotic equipment
  • Integrating PLCs with contemporary automation and robotics solutions
  • Supporting the implementation of smart manufacturing by seamlessly integrating with Industry 4.0
  • Ensuring successful automation and reliability in industrial processes
  • Enabling the integration of PLCs with higher-level systems and contemporary automation and robotics solutions.

Security and Safety Considerations

In light of the growing importance of cybersecurity in various sectors, it is imperative for PLCs to have enhanced security measures to safeguard against potential risks and ensure the safety of operations. Prevalent security risks in PLC programming encompass vulnerabilities in the PLC network, potential cybersecurity threats, and human errors that have the potential to compromise system integrity.

Recommended best practices for ensuring safety in PLC programming include:

  • Defining a structured logic for safety PLC
  • Utilizing safety function blocks and charts
  • Implementing input validation to prevent undefined states
  • Ensuring precise device use during programming
  • Maintaining comprehensive code documentation.

PLC programming has a direct impact on industrial process safety as it automates tasks to reduce human error and prioritizes the proper training and deployment of safety-focused PLCs.


From understanding the basics of PLC systems and setting up your PLC programming environment, to crafting your first PLC program and optimizing it for performance and scalability, we’ve covered a lot in this comprehensive guide to PLC programming. We’ve also delved into advanced techniques, fine-tuning and debugging your program, and the future of PLC programming in Industry 4.0.

It’s clear that the world of PLC programming is vast and constantly evolving, but with the right knowledge and tools, you can navigate it with ease and confidence. As we move towards an increasingly automated future, the skills and knowledge you’ve gained here will be invaluable. So, keep learning, keep exploring, and remember – the future is in your hands.

Frequently Asked Questions

How do I start PLC programming?

To start PLC programming, begin by identifying the problem and creating a sequence of operations using binary logic. Then, enter a program using a programming language and simulate it in your software for practice. Understanding the basics of ladder logic and PLC hardware components will also be essential.

Can you learn PLC programming on your own?

Yes, you can learn PLC programming on your own with free online resources and training available for ladder logic, function block diagrams, structured text programming, and SCADA systems.

What language is used for PLC?

The most popular languages used for PLC programming are Ladder Logic, Structured Text, Function Block Diagrams, Sequential Flow Charts, and Instruction Lists. These languages are commonly utilized for programming PLC systems.

What are the core components of a PLC system?

The core components of a PLC system include the CPU, I/O modules, and the power supply. These components are essential for the functioning of the system.

What are some advanced PLC programming techniques?

Advanced PLC programming techniques include utilizing structured text for scripting and data manipulation, and employing sequential function charts for process control. These techniques can enhance the functionality and efficiency of your PLC programming.