> For the complete documentation index, see [llms.txt](https://docs.voltmasters.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.voltmasters.io/dso-rtu/io-extension.md).

# IO extension

An **IO extension** is a device that gives the Voltmasters EMS a set of **digital inputs (DI)** and **relay outputs (DO)** over the installation network. The EMS reads the inputs for status feedback and drives the relay outputs to switch external circuits on or off.

The relay outputs are used in two ways:

* As a **hardware emergency stop** for [DSO RTU](/dso-rtu/how-telecontrole-works.md): a relay is wired into the installation's stop circuit and driven when the grid operator triggers an emergency stop. See [IO module emergency stop](/dso-rtu/io-module-emergency-stop.md).
* To switch a [**controllable load**](/device-integrations/controllable-loads.md) (a simple on/off load such as a heating element or pump) as part of the local control strategy.

{% hint style="info" icon="lightbulb" %}
The IO extension is the same physical hardware referred to as the **Moxa IO module** elsewhere in this section. "IO extension" is the device type as it appears on the platform.
{% endhint %}

### The hardware

* **Module:** Moxa ioLogik E1214 with 6 digital inputs (DI) and 6 relay outputs (DO).
* **Communication:** Modbus TCP/IP over the installation network.
* **Brand:** Moxa (the first supported brand).
* The relay outputs are potential-free contacts; the digital inputs are available for status feedback.

For where to place the module and how many you need, see [Installing the IO modules](/dso-rtu/io-module-installation.md).

### Adding the IO extension on the platform

Add the module like any other device:

* **Device type:** IO Extension
* **Brand:** Moxa — **Model:** ioLogik E1214
* **Connection:** Modbus TCP/IP, with the module's **IP address**, **port** and **Modbus slave ID** (noted during installation).

{% hint style="warning" %}
The IO extension must be in **managed** mode. A module set to *unmanaged* is only read, never written, so its relay outputs will not be actuated.
{% endhint %}

### Configuring the ports

Once the device is added, open its **Ports** page to configure each port. Every port has a **direction**:

| Direction         | Use                                                                                                                                                                                    |
| ----------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Digital Input** | Read-only status feedback from the installation; can also be assigned as an [emergency stop trigger](/dso-rtu/io-module-emergency-stop.md#triggering-an-emergency-stop-digital-input). |
| **Relay Output**  | Switches an external circuit; assign it a function (see below).                                                                                                                        |

For each **relay output** you can assign a function:

* **Telecontrol emergency switch** — drive the output from a DSO RTU emergency stop. See [IO module emergency stop](/dso-rtu/io-module-emergency-stop.md).
* **Controllable load** — switch an on/off load. See [Controllable load](/device-integrations/controllable-loads.md).

Outputs that are not assigned remain free for other uses.

### Manual override

A relay output can be **manually overridden** to a fixed **port state** (On or Off), for example during commissioning or maintenance. The override forces the output regardless of the normal control logic; clear it to return the port to automatic control.

### Deleting an IO extension

An IO extension **cannot be deleted while its ports are still in use** (assigned to an emergency stop or a controllable load). The platform shows which ports are in use and links to the **Ports** page so you can free them first.

### Next steps

* [Installing the IO modules](/dso-rtu/io-module-installation.md) — placement and cabling across cabinets.
* [IO module emergency stop](/dso-rtu/io-module-emergency-stop.md) — wire and configure a hardware emergency stop.
* [Controllable load](/device-integrations/controllable-loads.md) — switch an on/off load through a relay output.


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