PLCSim

Simulate PLC programs in Structured Text (IEC 61131-3) directly in VS Code — no hardware needed.

PLCSim runs your Structured Text programs inside VS Code with a real-time I/O simulator. Toggle boolean inputs, set integer values and watch outputs update live — without a physical PLC.

Features

Core simulation

• Real-time scan cycle — configurable cycle time with drift compensation (stable ±1ms at 10ms cycles)
• I/O panel — editable inputs (toggle BOOL, numeric INT/REAL); read-only outputs updated live
• Scan metrics — cycle time, jitter and overrun indicator in the simulator panel

Full IEC 61131-3 ST support

OPC-UA server (built-in)

• Starts automatically on port 4840 when the simulator opens
• Exposes all runtime variables as OPC-UA nodes (namespace ns=2)
• Configurable NodeId format per manufacturer (siemens-s7, rockwell, beckhoff, generic)
• Optional username/password authentication via opcua.config.json
• PLCSim: Configure OPC-UA — creates or opens opcua.config.json directly from the Command Palette
• Copy the OPC-UA URL to clipboard with PLCSim: Copy OPC-UA URL ✅ Pro

PLC dialect support ✅ Pro

Automatically detects and normalises vendor-specific syntax to standard IEC ST before execution:

• Siemens SCL — #localVar, "SymbolicName", typed constants (INT#5), REGION...END_REGION
• Beckhoff TwinCAT — direct addresses (%IX0.0, %QX0.0, %IW, %MW)
• Schneider Unity Pro — direct addresses (%I0.0, %Q0.0, %MW, %M)

TIA Portal export ✅ Pro

Export any .st file as .scl for direct import into Siemens TIA Portal via External Sources.

License status bar

While a .st file is active, the status bar shows your current tier at a glance:

Click the indicator to run PLCSim: Show License Info.

Commands

Free vs Pro

Early Adopters (installed before 2026-07-01) receive full Pro access automatically — no key needed.

Activate Pro by entering your license key in VS Code Settings → plcsim.licenseKey.
Purchase at plcsim.appscat.cat.

Getting Started

1. Install the extension
Search for PLCSim in the VS Code Extensions panel and click Install.

2. Open the example
Open the Command Palette (Ctrl+Shift+P / Cmd+Shift+P) and run:

PLCSim: Open Example

This copies 01-conveyor-belt.st into your workspace folder.

3. Open the simulator
With the .st file active in the editor, run:

PLCSim: Open Simulator

The simulator panel opens beside your code. Toggle bSensorIn to TRUE and watch bMotorBelt activate.

Example

(* Conveyor belt — PLCSim example *)
VAR
    bSensorIn    : BOOL;   (* Input sensor *)
    bSensorOut   : BOOL;   (* Output sensor *)
    bMotorBelt   : BOOL;   (* Belt motor *)
    iCount       : INT;    (* Parts produced *)
    iTarget      : INT;    (* Lot target *)
    bLotDone     : BOOL;   (* Lot complete flag *)
END_VAR

IF iTarget > 0 AND iCount >= iTarget THEN
    bLotDone   := TRUE;
    bMotorBelt := FALSE;
ELSIF bSensorIn AND NOT bLotDone THEN
    bMotorBelt := TRUE;
END_IF;

IF bSensorOut THEN
    iCount := iCount + 1;
END_IF;

Try it: set iTarget to 3, toggle bSensorIn ON, then toggle bSensorOut ON/OFF three times. Watch iCount increment and bLotDone activate.

OPC-UA Configuration

Create opcua.config.json in your workspace root to customise the server:

{
  "port": 4840,
  "nodeIdFormat": "siemens-s7",
  "plcName": "PLC",
  "dialect": "auto"
}

Requirements

• VS Code 1.85 or later
• No additional runtime, PLC software or internet connection required

License

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