---
title: URScript Callback Integration
description: "The URScript Callback integration lets you write custom URScript routines to control any power source that SmoothTool X does not have a built-in protocol plugin for. It is suited for advanced setups using protocols such as PROFINET, DeviceNet, or custom…"
url: "https://hub.smooth-robotics.com/docs/power-sources-urscript-callback/"
updated: "2026-09-23"
category: Power Sources
---

# URScript Callback Integration

The URScript Callback integration lets you write custom URScript routines to control any power source that SmoothTool X does not have a built-in protocol plugin for. It is suited for advanced setups using protocols such as PROFINET, DeviceNet, or custom Modbus configurations.

## Add the URScript Callback in SmoothTool X

Tap **SmoothTool X Settings** from the Application view. In the sidebar, under **Components**, tap **Power Sources**, then tap **Add new power source**.

 ![Power Sources page with the Add new power source button](https://hub.smooth-robotics.com/wp-content/uploads/2026/09/manual-power-sources-urscript-callback-power-sources-tab.webp)

In the **Add power source** dialog, select the **Independent Integrations** tile and choose the **URScript Callback** model, then tap **Add power source**.

 ![Add power source dialog — URScript Callback selected](https://hub.smooth-robotics.com/wp-content/uploads/2026/09/manual-power-sources-urscript-callback-add-power-source.webp)

### Load the welding scripts

The configuration page has two script editors — **Start welding function** and **Stop welding function**. You can type directly into either editor, or prepare the routine as a URScript file (`.script`, `.urscript`, or `.txt`) and tap **Load function** in the editor's header to load it. A syntax error is reported under the editor with the offending line highlighted. The trash icon clears an editor, after a confirmation.

Each editor also has a **Test run** button.

Warning

**Test run** executes that callback on the robot immediately — it is not a simulation. If a power source is connected, running the start welding callback strikes the arc, and it keeps welding until you stop it. SmoothTool X shows a **Welding may be active** banner with a **Run stop callback** action while the start callback has been run. Test the stop welding callback first, make sure you have another way to stop the arc (the emergency stop, or the power source's own switch), and make sure the area around the torch is clear.

   ![URScript Callback configuration page with the Start welding and Stop welding function editors](https://hub.smooth-robotics.com/wp-content/uploads/2026/09/manual-power-sources-urscript-callback-configuration.webp)

| Field | Description |
| --- | --- |
| Start welding function | URScript routine executed when SmoothTool X triggers the arc start. |
| Stop welding function | URScript routine executed when SmoothTool X triggers the arc stop. |

When done, tap **Done** to save the power source.

Safety relay configuration

If the robot program stops unexpectedly, the Stop welding function will not run, meaning the welding arc may remain active.

To prevent this hazard, take the **digital output that gates the arc** — the output your callback scripts drive and that is wired to the power source's hardware enable or safety circuit — and give it an action preset that reflects the program running state, so the arc is cut immediately if program execution stops.

This is **not** a fixed output such as DO0: use whichever output you actually wired to the power source's enable/safety input.

On the PolyScope X **I/O** screen, open that output and set its **Action Preset** so the signal moves to the state that **disables** welding whenever the program is not running:

- If the enable is **active-high** (signal HIGH allows welding — the recommended fail-safe wiring), choose **Low when not running** so the output drops to the disabled state on any stop.
- If the enable is **active-low** (signal LOW allows welding), choose **High when not running** instead.

The screenshot below uses **DO0** as an example, set to **Low when not running**.

 ![PolyScope X I/O screen showing an example digital output (DO0) with the Low when not running action preset](https://hub.smooth-robotics.com/wp-content/uploads/2026/09/manual-power-sources-urscript-callback-io-setup-do0.webp)

### Select the URScript Callback

Back on the **Power Sources** page, expand the new entry and tap **Selected** to make it the active power source. The URScript Callback runs your scripts directly rather than over a network connection, so there is no separate connect step.

 ![Configured URScript Callback power source entry](https://hub.smooth-robotics.com/wp-content/uploads/2026/09/manual-power-sources-urscript-callback-power-source-entry.webp)

The URScript Callback is now active and SmoothTool X is ready for welding.

## Callback examples

Save each routine as a script file, then load it with the **Load function** button under the matching editor.

### Example 1: Standard digital I/O handshake

Use this pattern when the power source is controlled via a digital output trigger and reports arc status via a digital input.

#### Start welding function

```python
set_standard_digital_out(0, True)

while (get_standard_digital_in(0) == False):
    sync()
end
```

#### Stop welding function

```python
set_standard_digital_out(0, False)

while (get_standard_digital_in(0) == True):
    sync()
end
```

---

### Example 2: PROFINET register communication

Use this pattern when the power source communicates over PROFINET using boolean and integer registers.

#### Start welding function

```python
# Wait until power source status register 0 reports ready (equals 0)
while (read_input_integer_register(0) != 0):
    sync()
end

write_output_boolean_register(0, True)

while (read_input_boolean_register(0) == False):
    sync()
end
```

#### Stop welding function

```python
# Wait until power source status register 0 reports ready (equals 0)
while (read_input_integer_register(0) != 0):
    sync()
end

write_output_boolean_register(0, False)

while (read_input_boolean_register(0) == True):
    sync()
end
```

## Programming with SmoothTool X and the URScript Callback

The URScript Callback has no welding parameters of its own — SmoothTool X only runs your Start welding and Stop welding functions — so a weld node shows no **Power source** tab for it.

Arc timing is still yours to set, as an arc setting: device-wide on the **Arc Settings** page under **Components** in the SmoothTool X Settings sidebar, or per weld node on the node's **Arc settings** tab. See [Arc Settings](/docs/usage-guides-arc-settings/).

Only the four wait times apply here. This integration reports no arc feedback — the weld-busy and current-flow signals echo the weld command SmoothTool X sent rather than the state of a real arc — so the arc timeouts and the arc-restart settings are hidden, and the tab says so.

| Identifier | Description |
| --- | --- |
| Wait before arc on | Waits before your Start welding function runs. |
| Wait after arc on | Waits after your Start welding function runs, before the robot starts moving. |
| Wait before arc off | Waits at the end of the path before your Stop welding function runs. |
| Wait after arc off | Waits after your Stop welding function runs, before the robot continues. |

## Simulation

The **Simulation** toggle in the Power source popover (opened from the button in the operator screen toolbar) runs the program as a dry run: the robot executes the full program and motion path, but the arc is never started — your Start welding and Stop welding functions are not executed. Use it to test a program safely, then turn it off to weld for real.