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An AI Chatbot for CODESYS: Write PLC Code by Talking to It

What if you could describe your PLC logic in plain English and get working Structured Text code back? AI chatbots for CODESYS are making this possible. Here's how it works and what to expect.

PLC Assist Team

An AI Chatbot for CODESYS: Write PLC Code by Talking to It

You've probably used ChatGPT or a similar AI chatbot to ask programming questions. Maybe you've even pasted some Structured Text into it and asked for help. It works -- sort of. But there's a gap between a general-purpose AI chatbot and one that actually understands your CODESYS project.

That gap is what specialized AI tools for PLC programming are closing.

The Problem with General AI Chatbots

If you open ChatGPT, Claude, or Copilot and ask "write me a function block for a conveyor motor", you'll get decent Structured Text code. These models have seen enough IEC 61131-3 examples to generate syntactically correct ST.

But here's what they can't do:

  • See your project: They don't know what function blocks you already have, what your GVLs contain, or how your project is structured
  • Match your style: They don't know if you use Hungarian notation, what your naming conventions are, or how you organize your code
  • Use your libraries: They don't know which CODESYS libraries are installed or what vendor-specific function blocks are available
  • Write to your PLC: They generate text in a browser window. You still have to copy-paste it into CODESYS, fix the formatting, and hope it compiles

It's like having a programmer who's never seen your codebase write code for you in a text editor. Helpful, but limited.

What a CODESYS-Specific AI Assistant Looks Like

A purpose-built AI assistant for CODESYS works differently:

It Sees Your Project

The AI can read your actual project tree -- every POU, GVL, DUT, and library reference. When you ask "add a method to FB_Motor", it knows FB_Motor exists, what its current interface looks like, and what methods it already has.

It Writes Directly to CODESYS

Instead of copying and pasting, the AI creates or modifies code directly in your CODESYS project. You review the changes, approve them, and they're applied. No clipboard gymnastics.

It Understands Context

Ask "add error handling to this function block" and it reads the current code, understands the logic, and adds appropriate error states, fault codes, and recovery logic -- fitted to what's already there.

Your Code Stays Local

This is the big one for industrial applications. Your PLC code doesn't get uploaded to a cloud server. The AI sees your project through a local bridge, and only your chat messages (the prompts) are sent to the AI service.

What You Can Ask

Here are real examples of what an AI chatbot connected to CODESYS can do:

Generate new code:

"Create a function block for a 3-position valve with manual override and position feedback timeout"

Modify existing code:

"Add a configurable ramp-up time to FB_SpeedController"

Explain code:

"What does the state machine in POU_MainSequence do?"

Debug:

"The motor starts but immediately stops. The interlock input is TRUE. What could be wrong in FB_Motor?"

Document:

"Add comments to FB_BatchProcess explaining each state"

Create data types:

"Create a DUT for recipe data with fields for temperature, pressure, speed, mix time, and ingredient ratios"

What to Watch Out For

AI for PLC programming is powerful but not magic. Keep these in mind:

Always Review Generated Code

AI can produce code that looks correct but has subtle logic errors. In PLC programming, a subtle error can mean a machine that behaves unexpectedly. Always read every line before deploying.

Safety-Critical Code Needs Human Judgment

Emergency stop logic, safety interlocks, SIL-rated functions -- these should be written and verified by qualified engineers. AI can help with the boilerplate around them, but the safety logic itself needs human expertise.

AI Doesn't Replace Domain Knowledge

The AI doesn't know your machine, your process, or your safety requirements. It generates code based on patterns. You need to know if those patterns are correct for your specific application.

Start with Low-Risk Code

Begin with utility function blocks, data structures, and documentation. Build trust in the tool before using it for production control logic.

How PLC Assist Does It

PLC Assist is a web-based engineering assistant that connects to CODESYS through a lightweight bridge script. You get:

  • An AI chat panel that sees your entire CODESYS project
  • Code generation that writes directly to your POUs, GVLs, and DUTs
  • A built-in code editor with syntax highlighting and autocomplete
  • One-click compile and save
  • Your code stays on your machine -- only chat messages go to the AI

It's the difference between asking a stranger for code advice and having an assistant who's sitting next to you, looking at your screen.

Try PLC Assist free -- 25 AI requests included, no credit card required.