IEC 61131-3 Programming Languages & CODESYS

 TL;DR

IEC 61131-3 is the global PLC language standard. Learn the five official languages, see how CODESYS and other IDEs fit in, and pick the right tool for your next automation project.

Quick-Start FAQ

                            
Why learn IEC 61131-3? It’s vendor-neutral: master it once, code on virtually any PLC.
Fastest way to practice? Download CODESYS or Open PLC, run the built-in soft-PLC simulator, and start coding today.
Biggest myth? “Ladder is the only real PLC language.” Modern plants lean heavily on ST and FBD for complex logic.

🔹 IEC 61131-3 in a Nutshell

Language Style Great For 1-Liner
Ladder Diagram (LD) Graphical Electricians migrating to PLCs “Rungs & coils—looks like relay logic.”
Function Block Diagram (FBD) Graphical Signal processing, PID loops “Plug-and-play logic blocks.”
Structured Text (ST) Textual Math, arrays, state machines “Pascal-ish code that reads like C.”
Instruction List (IL) Textual (deprecated) Legacy micro-PLC code “Assembly for controllers—now retired.”
Sequential Function Chart (SFC) Graphical Batch & step-sequence control “Flowchart for industrial recipes.”


CODESYS at a Glance

  • What it is: A free, vendor-independent IEC 61131-3 IDE with soft-PLC runtime.

  • Why you’ll love it:

    • Works on Windows, Linux, Raspberry Pi, and dozens of commercial PLCs.

    • One project file can target multiple CPUs—just pick the download device.

    • Built-in oscilloscope, field-bus configurators, and online change.

CODESYS-only extra features

Feature Use Case
CFC (Continuous Function Chart) Drag-anywhere, wire-anywhere data-flow programming—great for power users.
Visualization Toolkit Build HMI screens directly inside the PLC project.
Libraries & Git Integration Reuse code like normal software devs do.

IDEs That Speak IEC 61131-3

IDE Vendor Sweet Spot
TIA Portal Siemens S7-1200/1500 PLCs, unified HMI & drive config
Studio 5000 Rockwell Allen-Bradley ControlLogix & CompactLogix
TwinCAT 3 Beckhoff PC-based automation, integrates directly with Visual Studio
EcoStruxure Control Expert Schneider Modicon M340/M580, safety PLCs
Sysmac Studio Omron NX/NJ series, integrated robotics
GX Works 3 Mitsubishi iQ-R/iQ-F families, Japanese market leader
e!COCKPIT WAGO PFC controllers; CODESYS engine under the hood
ISaGRAF 6 Rockwell / ICS Triplex SIL-rated safety & distributed control
OpenPLC Open-source Hobby, education, quick PoCs—runs on a Pi

 Mini Code Sample (Structured Text)

(* Toggle a motor if temperature > 75 °C and not already running *)
IF (Temp > 75.0) AND NOT MotorRun THEN
    MotorRun := TRUE;
END_IF;

Paste that into CODESYS ST editor, hit Online → Simulation, and watch the boolean flip in real time.

 Key Takeaways

  1. Standards = Portability. Learning IEC 61131-3 frees you from vendor lock-in.

  2. Start free, then specialize. Practise on CODESYS/OpenPLC; move to TwinCAT or TIA Portal when project specs dictate.

  3. ST is the future. Modern plants rely on textual code for maintainability and version control.

  4. Keep learning. Safety PLCs (SIL2/3) and Industry 4.0 require the same core languages plus strong networking know-how.

 Where to Go Next

  • Download CODESYS (codesys.com) → Tools > Store for Raspberry Pi soft-PLC.

  • GitHub → OpenPLC: free runtime & examples.

  • Read the spec: IEC 61131-3 ed. 3.0 (2013) — available via IEC webstore.

  • Grab a cheap PLC: WAGO PFC200 or Siemens S7-1200 starter kit to practise on real I/O.


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