IEC 61131-3
CODESYS for Free: Learn IEC 61131-3 Without Buying a PLC
The vendor-neutral way into PLC programming: what the free CODESYS download includes, which brands build on it, and how to practise all the IEC languages.
Free CODESYS training is the most direct way to learn IEC 61131-3 without buying a PLC. The CODESYS Development System costs €0.00 in the CODESYS Store, it comes with a demo soft PLC that runs on your Windows PC, and the skills carry over to controllers from makers such as ABB, WAGO, Bosch Rexroth and Schneider Electric.
Checked 26 September 2026 on the CODESYS Store and on each maker's own site.
Why learn a PLC that is not a brand
Most PLC courses teach one maker's software. That is the right call when you know which controllers you will work on. But if you are a student, changing industry, or working with machines whose controllers are built on CODESYS, a vendor-neutral start makes sense.
CODESYS is a development system for IEC 61131-3, the international standard for PLC programming languages. Many hardware makers license it and build their own tools on top. Learn CODESYS, and you have learned most of what those tools do. What changes from brand to brand is mainly the hardware configuration and the libraries.
What the free download actually includes
The CODESYS Store lists the CODESYS Development System (version 3.5.22.30 when we checked) at €0.00, in 32-bit and 64-bit versions. The setup includes a demo of CODESYS Control Win SL, a soft PLC that turns a Windows PC into a controller.
The limit is simple. CODESYS's data sheet says that in demo mode the soft PLC runs for two hours without a licence, after which you restart it by hand. For a study session that is no real limit, and it is why this is the best codesys free version route: nothing is time-bombed on the calendar, and you can return to it whenever you like.
The store's licence terms also explain the pattern you will see: software marked "Free" can be used free of charge, while demo licences are free but limited by time or function. The Development System is in the first group; the runtime demo is in the second.
Which brands run CODESYS underneath
We only list makers who say it on their own pages.
- ABB says Automation Builder, the tool for its AC500 PLCs, is built on CODESYS and fully compliant with IEC 61131-3. ABB also offers a free Basic licence.
- WAGO says CODESYS V3 will be available for its control solutions, and describes CODESYS V3.5 as free of charge to start programming.
- Bosch Rexroth says it has offered CODESYS programmable controllers since 2003, and its ctrlX PLC app uses additional CODESYS libraries.
- Schneider Electric publishes a FAQ on which CoDeSys compiler version each release of EcoStruxure Machine Expert uses.
That is four major makers, and the CODESYS device directory lists many more. The practical point: an engineer fluent in CODESYS can sit down at any of these tools and be productive quickly.
The IEC 61131-3 languages, in one table
The IEC's own summary of the 2013 edition names two textual languages (Instruction List and Structured Text) and two graphical ones (Ladder Diagram and Function Block Diagram). The standard also defines Sequential Function Chart, for organising a program into steps and transitions, which is why most courses, this one included, count five. CODESYS adds a sixth editor, Continuous Function Chart.
Which to learn first? Ladder, because every maintenance engineer reads it and it maps directly to the relay circuits it replaced. Then structured text, because anything involving maths, arrays or loops is shorter and clearer in ST. SFC comes third, once you have a machine sequence to organise. Instruction List is worth being able to read, since you will meet it in older programs.
The same rung in ladder and in structured text
The best way to see what IEC 61131-3 gives you is to write one piece of logic twice. A motor start/stop with a seal-in in ladder is two contacts in parallel, one in series and a coil. In structured text it is a single line:
MOTOR := (START_PB OR MOTOR) AND NOT STOP_PB;
Read it aloud and it says exactly what the rung says: the motor runs if start is pressed or it is already running, and stop is not pressed. Neither form is better. Ladder is easier to fault-find on a live machine because you can see power flow. Structured text is easier once there are calculations, loops or arrays. A good engineer uses both in the same project, and CODESYS lets you do that freely.
Function blocks: the idea that travels
The single most useful thing CODESYS teaches is the function block. You write the logic for one motor once, as a block with inputs (Start, Stop, Overload) and outputs (Run, Fault). Then you create one instance per motor: Conveyor1, Conveyor2, Pump. Fix a bug in the block and every motor is fixed.
This is how modern machine software is built, and it is the same idea as Siemens' function blocks with instance data blocks, Rockwell's Add-On Instructions and Beckhoff's TwinCAT function blocks. Learn it properly in CODESYS and those tools will feel familiar.
What CODESYS will not teach you
Be realistic about the gaps. Each maker adds its own hardware configuration, fieldbus set-up, libraries and safety tools on top of CODESYS, and those you learn on the brand's own tool. CODESYS also will not teach you a vendor's diagnostics screens or firmware updates. Treat it as the foundation, then add one brand.
How to practise without hardware
A few habits make CODESYS practice productive:
- Write the same logic twice. Build a start/stop in ladder, then in ST. Seeing the same behaviour in two languages is the fastest way to understand both.
- Use function blocks early. Wrap your motor start/stop in a function block with inputs and outputs, then call it three times for three motors. That is the core idea of IEC 61131-3, and it transfers everywhere.
- Watch the online view. When logged in to the soft PLC, CODESYS shows live values beside your code. Change an input and follow the result rung by rung, or line by line.
- Add a visualisation. A simple screen with a button and a lamp makes your program feel like a machine, and it is where HMI skills begin.
Who this route suits
CODESYS is a good first PLC tool for three kinds of learner:
- Students and career changers who do not yet know which brand their first employer will use. The IEC foundation is useful whatever comes next.
- Engineers joining machine builders that use CODESYS-based controllers, where the tool itself is the job.
- Software developers moving into automation, who will find structured text, function blocks and libraries far more familiar than ladder-only tools.
It suits less well if you already know you will maintain a Siemens or Allen-Bradley plant. In that case, start with the vendor's own software, such as the Siemens TIA Portal or Micro800 with CCW courses, and come back to CODESYS for the IEC depth.
Where to go after CODESYS
Once the IEC ideas are solid, pick a brand. If your target is PC-based control, Beckhoff TwinCAT 3 is a natural next step. Beckhoff says the core of TwinCAT 3 Engineering is free and runtime trial licences last seven days and can be renewed any number of times. If you work with ABB drives and PLCs, Automation Builder is the obvious follow-on. If you want to see your program drive real outputs cheaply, OpenPLC runs IEC 61131-3 programs on Arduino and Raspberry Pi boards.
The IEC 61131 and software PLCs path groups CODESYS, TwinCAT 3 and ABB Automation Builder in that order. OpenPLC is a good side project at any point.
Take the free CODESYS course
The CODESYS and IEC 61131-3 course is free in full. It runs from the first project through contacts and coils, logic gates, latching, timers and counters, function blocks, FBD and structured text, CFC, SFC and visualisation, ending in a final assessment of 15 questions (60% to pass, three attempts). Video lessons are by independent YouTube creators, credited on the course page; EDWartens writes the study plan, notes, practice tasks and assessment. You need a free account to save progress, and no card.
The only paid item is optional. After you pass, an EDWartens Certificate of Completion for this course, which starts at beginner level, costs from US$2.99, and checkout shows your price. The TwinCAT 3 course is intermediate, so its certificate costs a little more. Anyone can check a certificate at edwartens.com/verification. It is not a CODESYS, Beckhoff or ABB certification, and it is not accredited or a university qualification.
Take the free course
Questions
Is there a free version of CODESYS?
Yes. The CODESYS Development System is listed at €0.00 in the CODESYS Store, and its setup includes a demo of the CODESYS Control Win SL soft PLC. The demo runs for two hours at a time, then needs a manual restart.
Can I learn CODESYS without a PLC?
Yes. The demo soft PLC runs on your Windows PC, so you can download, run and debug programs with no hardware. Our free CODESYS course is built entirely on it.
Which PLC brands use CODESYS?
ABB says its Automation Builder is built on CODESYS, WAGO makes CODESYS V3 available for its controllers, Bosch Rexroth has offered CODESYS controllers since 2003, and Schneider Electric's Machine Expert uses a CODESYS compiler. Check each maker's page for the exact products.
What are the IEC 61131-3 programming languages?
Ladder Diagram and Function Block Diagram (graphical), Structured Text and Instruction List (textual), plus Sequential Function Chart for organising a program into steps. CODESYS adds Continuous Function Chart.
Is a CODESYS course useful if my plant runs Siemens?
Partly. The IEC ideas, such as function blocks, structured text and timers, carry over to TIA Portal's SCL and FBD. But you will still need to learn Siemens' own software, so treat CODESYS as a foundation, not a replacement.
Sources
- CODESYS Store: CODESYS Development System
- CODESYS: Control Win SL data sheet (demo mode)
- IEC: IEC 61131-3:2013 Programming languages
- ABB: Automation Builder
- WAGO: CODESYS V3
- Bosch Rexroth: CODESYS partner page, ctrlX AUTOMATION
- Schneider Electric FAQ: CoDeSys compiler version per Machine Expert version
- Beckhoff: TwinCAT 3 licensing
Written by the EDWartens engineering team for general education. Product names are trademarks of their owners; mentioning them does not imply endorsement. Prices and terms of other providers were checked on the date shown and can change.
