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AI for PLC Programming: How It Works and Why It Matters

AI is transforming how automation engineers write PLC code. Learn how AI-assisted Structured Text generation works, what it can and can't do, and how to use it safely in industrial projects.

PLC Assist Team

AI for PLC Programming: How It Works and Why It Matters

The manufacturing floor is one of the last places you'd expect to see AI code generation. PLC programming has always been a hands-on discipline -- engineers write ladder logic, structured text, or function block diagrams with extreme care because a single bug can halt a production line or, worse, create a safety hazard.

But AI is starting to change that, and for good reason.

The Problem with Traditional PLC Development

Writing Structured Text (ST) for CODESYS or any IEC 61131-3 environment is slow. Here's why:

  • Boilerplate everywhere: Every function block needs VAR declarations, input/output definitions, and method scaffolding. A simple motor controller FB can easily be 80+ lines before you write any logic.
  • Repetitive patterns: Most industrial code follows well-known patterns -- PID controllers, state machines, alarm handlers, interlocks. Engineers rewrite these from scratch or copy-paste from old projects.
  • Documentation debt: Comments and documentation are always the first thing to skip under deadline pressure. Six months later, nobody remembers why that IF condition exists.
  • Limited tooling: Most PLC IDEs haven't changed much in 20 years. No autocomplete, no inline docs, no refactoring tools.

How AI-Assisted PLC Programming Works

Modern AI code assistants use large language models (LLMs) trained on vast amounts of code. When applied to PLC programming, here's what happens:

1. You Describe What You Need

Instead of writing every line manually, you describe the behavior in plain English:

"Create a function block for a conveyor motor with start/stop control, overcurrent protection, and a runtime counter."

2. The AI Generates Structured Text

The AI produces complete, syntactically correct IEC 61131-3 code:

FUNCTION_BLOCK FB_ConveyorMotor
VAR_INPUT
    bStart      : BOOL;
    bStop       : BOOL;
    rCurrent    : REAL;  // Motor current in Amps
    rMaxCurrent : REAL := 15.0;  // Overcurrent threshold
END_VAR

VAR_OUTPUT
    bRunning     : BOOL;
    bOvercurrent : BOOL;
    tRuntime     : TIME;
END_VAR

VAR
    tonRuntime : TON;
    bMotorCmd  : BOOL;
END_VAR

3. You Review and Deploy

This is the critical part. AI-generated code must always be reviewed by a qualified engineer before deployment. The AI doesn't know your specific machine, safety requirements, or plant standards.

What AI Can Do Well

  • Generate boilerplate: VAR declarations, FB scaffolding, method signatures
  • Implement standard patterns: State machines, PID wrappers, alarm logic
  • Add comments and documentation: Explain existing code or generate inline docs
  • Convert between styles: Transform ladder-style logic to structured text
  • Suggest improvements: Identify potential issues in existing code

What AI Can't Do (Yet)

  • Replace safety engineering: AI doesn't understand SIL levels, safety PLCs, or machine-specific risk assessments
  • Know your hardware: It doesn't know your I/O mapping, network topology, or drive parameters
  • Guarantee correctness: Every line must be verified against your specification
  • Handle real-time constraints: AI doesn't reason about scan times, task priorities, or deterministic timing

Using AI Safely in Industrial Projects

If you want to use AI for PLC programming, follow these rules:

  1. Always review generated code line by line before deploying
  2. Test in simulation first -- never deploy AI-generated code directly to a production PLC
  3. Keep safety-critical logic manual -- interlocks, e-stops, and SIL-rated functions should be written and verified by hand
  4. Use AI for the boring parts -- boilerplate, documentation, and repetitive patterns are where AI saves the most time with the least risk
  5. Validate against your specification -- AI doesn't read your functional design document

The Future of PLC Development

AI won't replace PLC programmers. But PLC programmers who use AI will be significantly faster than those who don't. The key is knowing where to apply it and where to keep human judgment in the loop.

Tools like PLC Assist are built specifically for this workflow -- connecting AI assistance directly to your CODESYS project while keeping your code local and under your control.

The engineers who adopt AI-assisted development now will have a significant advantage as the technology matures. The ones who wait will eventually have to catch up.

PLC Assist is an AI-powered engineering assistant for industrial automation that helps automation engineers write Structured Text faster. Try it free -- no credit card required.