Overview

The IronPLC extension brings IEC 61131-3 Structured Text support to your development environment. It provides real-time feedback as you write code, helping you catch errors before deployment.

Supported Languages

IEC 61131-3 Structured Text

The primary language supported by IronPLC.

File Extensions:

.st, .iec

The extension provides:

  • Syntax highlighting for keywords, types, comments, strings, and numbers

  • Automatic bracket matching for block keywords (IF/END_IF, FUNCTION/END_FUNCTION, etc.)

  • Real-time diagnostic analysis

VS Code showing an IEC 61131-3 Structured Text file with syntax highlighting

Structured Text with syntax highlighting in VS Code.

PLCopen XML

XML format for IEC 61131-3 projects as defined by PLCopen TC6.

The extension detects PLCopen XML files by looking for the PLCopen namespace in the opening XML tags. It provides XML syntax highlighting with embedded Structured Text support inside CDATA sections.

TwinCAT

Beckhoff TwinCAT 3 project files containing IEC 61131-3 source code.

File Extensions:

.TcPOU, .TcGVL, .TcDUT

The extension provides XML syntax highlighting with embedded Structured Text support and real-time diagnostic analysis.

Commands

New Structured Text File

Creates a new untitled file with the Structured Text language mode pre-selected.

Menu Location:

File ‣ New File… ‣ Structured Text File

To use this command:

  1. Open the Command Palette (Ctrl+Shift+P or Cmd+Shift+P)

  2. Type “New Structured Text File”

  3. Press Enter

Build Tasks

The extension provides a build task that compiles your project to a bytecode container (.iplc) file. Use Ctrl+Shift+B to run the build task. See Build Tasks for details.

Bytecode Viewer

Opening an .iplc bytecode file displays a human-readable disassembly of the compiled program, including the file header, constant pool, and function instructions with color-coded opcodes. See Bytecode Viewer for details.

VS Code custom editor showing disassembled IPLC bytecode with color-coded opcodes

The bytecode viewer showing a disassembled .iplc file.

Diagnostics

The extension reports diagnostics from the IronPLC compiler in real-time:

  • Errors (red underline): Code that will not compile

  • Warnings (yellow underline): Code that may indicate problems

Each diagnostic includes a problem code (e.g., P0001) linking to documentation that explains the issue and how to resolve it. See Problem Codes for the complete list.

VS Code editor showing red and yellow diagnostic squiggles on invalid Structured Text code

Diagnostics with error squiggles and problem codes.

Open the Problems panel (Ctrl+Shift+M or ⌘+Shift+M) to see all diagnostics in a list with their problem codes.

VS Code Problems panel listing IronPLC diagnostic errors with problem codes

The Problems panel showing diagnostics with problem codes.

Run Program

The extension adds a Run Program code lens above each PROGRAM declaration. Click it to compile and execute the program using the IronPLC runtime.

VS Code editor showing the Run Program code lens above a PROGRAM declaration

The Run Program code lens above a PROGRAM declaration.

While the program is running, the code lens changes to Stop and Pause controls.

VS Code editor showing Stop and Pause code lenses while a program is running

Stop and Pause controls replace Run Program while the program executes.