OPC DA (classic OPC) communication

OPC DA is the classic, Windows-specific OPC interface (COM / DCOM). The driver connects as a client to an OPC DA 2.05a server and uses no port. The server can be on this computer or on another computer on the network.

Use this driver if a device can be reached only through an OPC DA server. If the server also offers OPC UA, prefer the OPC UA driver.

• Local server: the Windows user running Live stays selected as the DCOM identity. If the server runs with another account, that account must have permission to launch and access the server.
• Remote server: in the DCOM settings of the OPC server on the remote computer, grant launch and access permission to the connecting user. If you choose a user name and password, you can use the form ALAN\kullanıcı.
• DCOM / RPC traffic must be open in the firewalls between the Live computer and the server. Before connecting to a remote server, check the permissions and the firewall on the server computer.
• The password is entered in Live with the Enter password button under Connections in the system menu; the Settings authorization is required. The password you enter is stored unencrypted in the baglanti_sifreleri.json file on the Live computer; open the project data folder only to the account that runs Live.

• The syntax of the item ID belongs to the server. Studio only checks that it is not empty, contains no control characters and does not exceed 1024 characters; the server does the validation. A wrong ID appears in Live as a tag error.
• Several OPC DA connections, each with a different ProgID, can be defined to the same computer.

WString is not supported; OPC DA strings are already Unicode, so use String. Array tags are not supported. A write is made as a single value, converted to the data type of the item on the server.

• The driver opens a single active OPC group and adds one item per tag (at most 250 items per request). Reading is done in bulk (at most 500 items per request).
• Quality: if the server reports the quality as good or uncertain, the value is used. If it is bad, the tag gets an error. While the server is waiting for the first data, the tag stays in the waiting state and gets no error.
• A written tag is read back at once. If the connection drops, the driver retries after 1 s, 2 s and 5 s, then every 10 s. For the behavior common to all drivers see the communication drivers page.

• It is an OPC DA 2.05a client only. There is no OPC HDA or OPC A&E, and no data is offered as an OPC DA server.
• The driver is Windows-specific (COM).

Connection messages appear in the Connections section of the system menu in Live. For tag errors during reading no message is shown; the tag only gets bad quality.