plcc

Write PLC programs in ladder or Structured Text, and run them on open hardware.

plcc is an open-source compiler for IEC 61131-3, the standard language family of industrial controllers. It turns ladder logic and Structured Text into native machine code for whatever chip you have, and reads the project files engineers already use: Rockwell Studio 5000, Beckhoff TwinCAT, CODESYS, and OpenPLC.

Open plcc studio → the ladder editor, in Chrome or Edge.

What you can do

• Edit ladder in the browser. Draw rungs or type them (XIC Start XIO Stop OTE Motor), simulate them, and watch a real PLC live over USB. Nothing to install; projects stay in your browser.
• Bring existing programs. Rockwell .L5X, Beckhoff TwinCAT projects, and PLCopen XML (exported by CODESYS, OpenPLC and others) compile as they are.
• Translate between them. Ladder to Structured Text and back, IEC ladder to Rockwell ladder and back, with a warning wherever two vendors' instructions behave differently.
• Run it on real hardware. Native code for ARM, x86, RISC-V or WebAssembly. Each board is described by a small device manifest; the Arduino Opta is the first.

How it fits together

flowchart LR
    subgraph Sources
        studio["plcc studio<br/>(ladder editor)"]
        st["Structured Text<br/>.st"]
        l5x["Rockwell<br/>.L5X"]
        tc["Beckhoff TwinCAT<br/>.plcproj"]
        xml["PLCopen XML<br/>CODESYS, OpenPLC"]
    end

    plcc{{"plcc<br/>check · translate · compile"}}

    subgraph Runs on
        opta["Arduino Opta<br/>and other ARM PLCs"]
        linux["Linux PLCs<br/>and PCs"]
        sim["Browser<br/>simulator"]
    end

    studio --> plcc
    st --> plcc
    l5x --> plcc
    tc --> plcc
    xml --> plcc
    plcc --> opta
    plcc --> linux
    plcc --> sim
    manifest[("device manifest<br/>I/O, flashing, console")] -.-> plcc

A compiled program doesn't know which board it runs on. It reads inputs and writes outputs through a standard process image (%I, %Q, %M), and a small runtime written once per board connects that image to the real terminals.

Try it

1. Open plcc studio, pick Simulate, and flip the virtual StartPB input.
2. Or compile from the command line:

   plcc compile motor.st -o motor.o --device arduino-opta
   

   Building plcc and every other command: docs/development.md and docs/cli.md.

Status

plcc is young and moving fast. What has been shown to work:

• The compiler: the full Structured Text language, about 1,000 automated tests, and the 559-file OSCAT library compiling as one program.
• Real hardware: ST, PLCopen ladder and Rockwell ladder programs have each run on an Arduino Opta, switching its relays and talking Modbus RTU.
• Real projects: 71% of public hand-made L5X exports compile, and every public TwinCAT project tested parses (most of the rest need Beckhoff's own libraries).

Still experimental: the studio's online connection to real hardware, flashing from the browser, compiling inside the browser, and plcrt, our own bare-metal runtime. Known gaps are listed in docs/known-issues.md.

Learn more

Language support	What compiles, the standard library, targets
Command line	Every plcc command and input format
Running programs	The runtime contract and hardware abstraction layer
Ladder · Translation	Ladder formats, IEC ↔ Rockwell mapping
Rockwell L5X · TwinCAT · CODESYS	Vendor formats and behaviour
Device manifests	Describing a board
Developing plcc	Layout, building, tests

License

Mozilla Public License 2.0, with a compiler output exception: programs you compile with plcc carry no license obligation, and you can link the runtime into a proprietary product. Improvements to plcc's own files come back under the MPL. Device manifests are CC0.

Contributions are welcome, signed off under the DCO. No CLA.