Debugger

The debugger lets you watch live variable values from a running vPLC, charted over time. It uses a custom Modbus PDU (function codes 0x41–0x45) over WebSocket (Runtime v4) or Modbus TCP (Runtime v3) to read variable values out of the runtime on a tight polling loop.

There's no breakpoint / step support, this debugger is live inspection only.

Prerequisites

  • The editor is connected to a vPLC. See Connecting to a vPLC.
  • You've opted in the variables you want to watch (Debug column checkbox in the variables table, see Variables editor).

Opening the debugger

Click the bug icon in the activity bar (between Play and AI).

What happens behind the scenes:

  1. The editor saves the project (if dirty).
  2. The compiler runs a debug build, same as a release build, plus a .dbg symbol map and an MD5 hash of the compiled program.
  3. The editor compares the local MD5 against the one currently running on the vPLC (runtime.readProgramMd5).
    • Match → the debug session starts.
    • Mismatch → a dialog prompts you to upload. Confirm to ship the build and start.

The console reports each step.

What you see

The debugger panel replaces the console at the bottom of the editor.

It contains a line chart:

  • X axis: elapsed time. The default window is 10 seconds; the buffer keeps 10 minutes of history.
  • Y axis: variable values. Multiple variables share the chart; the legend on top lets you toggle each line.
  • Boolean variables render at the top or bottom of the chart with sharp transitions.
  • Numeric variables (REAL, INT, etc.) get normalised to the same Y range so they share the chart cleanly.

Controls along the top:

  • Pause / Play: freeze the chart (the polling keeps running in the background; resume to see what happened).
  • Range selector: pick the visible time window (1 s, 5 s, 10 s, 30 s, 1 min, 5 min, 10 min).
  • Elapsed clock: total session time.

Opting variables in

In the variables table for any POU, tick the Debug column. Only ticked variables are polled. Tick fewer for more responsive polling; tick more for broader coverage.

You can change the selection mid-session. Newly ticked variables join the chart on the next poll cycle (typically < 200 ms).

Limitations

  • No breakpoints. The IEC runtime doesn't support pause/step semantics. This debugger is a watcher, not a control surface.
  • No history before connection. The debugger only starts buffering once the session begins. Variables that change in the milliseconds before you open the debugger aren't recoverable.
  • Numeric scaling is global. All numeric variables share one Y axis. Mix a REAL in the range 0…1 with an INT in 0…1000 and the small one will look flat, toggle the big one off in the legend to zoom in on the small one.

Troubleshooting

MD5 mismatch prompt. The build on disk is newer than what's running on the vPLC. Accept the upload to sync them.

Variables flat at zero. Confirm the variable is actually ticked in the Debug column, and that the PLC is Running (Play button in the activity bar should be coloured-in / pressable).

Polling stalls. The runtime connection dropped. The console shows a transport error. Reconnect from the Orchestrators panel.

The bug icon is grey. You're not connected to a runtime. Open the Orchestrators screen and connect first.

What's next