> For the complete documentation index, see [llms.txt](https://help.security.gallagher.com/knowledge-hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.security.gallagher.com/knowledge-hub/products/cc-software/configure/interface-options/ole-for-process-control-opc.md).

# OLE for process control (OPC)

Understand legacy OPC Data Access and Alarm and Event interfaces.

OPC is OLE for Process Control.

> ⚠️ OPC support is limited. Gallagher recommends newer interface options such as the [REST API](/knowledge-hub/products/cc-software/configure/interface-options/api/representational-state-transfer-rest-api/rest-api-features.md).

Two types are used with Command Centre.

| Type                                      | What it does                                                                                                                                                                  | Licence                                                 |
| ----------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------- |
| **OPC Data Access (OPC DA v2.05B, v3.0)** | An OPC DA client interfaces directly with Command Centre. It can query item status (doors, relays, and so on) and display it, and issue commands (override doors and relays). | Requires **`OPCDataServer=1`** in the site licence file |
| **OPC AE (Alarm and Event)**              | Command Centre acts by default as an **OPC Alarm and Event Server**. All alarm and event data is available to an OPC client, which filters as required.                       | No licence strings required                             |

***

🔗 **Related**

* [REST API - Features](/knowledge-hub/products/cc-software/configure/interface-options/api/representational-state-transfer-rest-api/rest-api-features.md). The recommended modern interface.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://help.security.gallagher.com/knowledge-hub/products/cc-software/configure/interface-options/ole-for-process-control-opc.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.