> For the complete documentation index, see [llms.txt](https://documentation.nomos-system.com/nomos-system/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.nomos-system.com/nomos-system/integrator-en/administration/usb-serial-vpn.md).

# USB Serial over VPN

With **"Expose a local USB device to VPN"** the controller makes a connected USB serial adapter available as a TCP port. This lets you remotely program bus systems whose configuration software needs direct serial access — just as if the adapter were plugged into your own computer.

{% hint style="info" %}
The share is reachable via the [Direct-VPN](/nomos-system/integrator-en/administration/vpn.md), the [Support VPN](/nomos-system/integrator-en/administration/support-vpn.md) and on the local network.
{% endhint %}

## Enable the share

1. Open the VPN page and click **"Expose a local USB device to VPN"**.
2. Select the **serial port** (the USB adapter), the **baudrate** (must match the connected hardware) and the **TCP port** (default: 3001).
3. After saving, the overview shows the state of the share: **Running**, **Connected** or **Adapter not connected**.

## Set up the client on Windows

On Windows you create a **virtual COM port** that points at the controller's TCP port — for example with the free **HW VSP3** (single-port edition, [hw-group.com](https://www.hw-group.com/software/hw-vsp3-virtual-serial-port)):

1. Download and install HW VSP3 (the "Standalone" edition).
2. On the **"Virtual Serial Port"** tab choose a free **COM port** (e.g. COM5), enter the controller's VPN IP address as **IP Address** and the configured TCP port (default: 3001) as **Port**.
3. On the **"Settings"** tab **disable "NVT enabled"** — the connection uses raw TCP.
4. Click **"Create COM"** to create the virtual COM port.

Then select the new COM port in your programming software and configure the same **baudrate** as in the share (data format 8N1).

## Set up the client on macOS / Linux

On macOS and Linux, `socat` does the job (macOS: install with `brew install socat`):

```
socat pty,link=/tmp/ttyNOMOS,raw,echo=0 tcp:<VPN-IP>:3001
```

While the command is running, `/tmp/ttyNOMOS` is available as a serial port and can be selected in the programming software.

## Notes

{% hint style="warning" %}

* **One connection at a time** — disconnect the client before another one connects.
* The **baudrate** of the share must match the connected hardware (data format 8N1).
* The USB adapter must be **plugged into** the controller — the status indicator in the overview shows the current state.
  {% endhint %}


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