# OPC DA client (OPC Classic)

> Bring existing OPC DA servers such as RSLinx Classic, SIMATIC NET or vendor OPC servers into PLCGateway and make them available over OPC UA.

Many plants still run OPC DA servers that connect older controllers. PLCGateway's OPC DA client on Windows reads these servers through the classic COM interfaces, locally or on another computer over DCOM.

The servers installed on a computer are listed through OPCEnum, the item tree can be browsed, and reads come from the server cache or directly from the device. Combined with PLCGateway's OPC UA server this is a straightforward way to migrate OPC Classic data to OPC UA.

- **Driver id:** `opcda_client`
- **Connection:** COM / DCOM · Windows
- **Address browsing:** yes
- **Writing:** yes
- **Included in:** PLCGateway Connect, PLCGateway SCADA, PLCGateway Embedded

## What PLCGateway reads and writes

- Items of OPC DA 1.0, 2.0 and 3.0 servers through the DA 2.0 interfaces
- Server discovery through OPCEnum
- Browsing of branches and leaves with type and access rights
- Cache or device reads
- Remote servers over DCOM with domain, user and password
- Writing of items

## Address examples

| Address | Meaning |
|---|---|
| `Line1.Motor1.Speed` | ItemID of the server |
| `[PLC1]N7:0` | RSLinx Classic topic and address |
| `S7:[S7 connection_1]DB1,REAL0` | SIMATIC NET item |

## Controllers and devices

- [Allen-Bradley (Rockwell Automation)](https://plcgateway.com/controllers/allen-bradley.md)
- [Siemens SIMATIC](https://plcgateway.com/controllers/siemens.md)

## Connect in a few steps

1. Install PLCGateway on Windows on the same computer as the OPC DA server, or configure DCOM for a remote server.
2. Add an OPC DA device and use server discovery to select the ProgID.
3. Browse the item tree and add the items as tags.
4. Publish the values through PLCGateway's OPC UA server for modern clients.

## Questions and answers

### Does the OPC DA client work on Linux?

No. OPC DA is based on Windows COM/DCOM. On Linux, use an OPC UA wrapper of the OPC DA server and the OPC UA client.

### Can PLCGateway replace an OPC UA wrapper?

Yes. PLCGateway reads the OPC DA server and publishes the values in its own OPC UA server, with security and user management.

### Is DCOM configuration needed?

Only for remote servers. On the same computer the connection works without DCOM settings.

## Related protocols

- [OPC UA client](https://plcgateway.com/protocols/opc-ua.md)
- [Allen-Bradley EtherNet/IP (CIP)](https://plcgateway.com/protocols/ethernet-ip.md)
- [All protocols](https://plcgateway.com/protocols.md)

_Product and model names are trademarks of their owners. They are named only to show which equipment the drivers communicate with; PLCGateway is not affiliated with these companies._

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Source: https://plcgateway.com/protocols/opc-da