Using CitectSCADA > Communicating with I/O Devices > Setting Up Communications > Express Communications Wizard - Link to external database

Express Communications Wizard - Link to external database

This screen allows you to link to an external data source.



Link I/O Device to an external tag database

Determines whether or not you want to link the I/O Device to an external data source. If you link to an external data source, CitectSCADA is updated with any changes made to the external data source when a refresh is performed.

If you disconnect an existing link, you can choose to make a local copy of the tags in the data source or you can delete them from CitectSCADA's variable tags data source altogether.

Database type

The format of the data referenced by the external data source.

External tag database

Specify the location of the external database. This could either be a path and filename of the external data source for the I/O Device, or the IP address/directory, computer name, or URL of a data server, etc. (for example "Work.CSV" or "", "\HMI_SCADA" or "" or "\\coms\data\scada").

Depending on the database type selected, the browse button could:

display a standard Windows file browse dialog to browse for the external database.

display a modal dialog to browse in a tree view of servers on the network connected to the computer.

display the Unity Link Configuration Properties dialog.

Connection string

Enter a connection string to provide connection details for the data source. This is similar to an ODBC connection string. For example:

UserID = XXX; Password = YYY


ServerNode=; Branch=XXX

Not every data source requires a connection string.

Add prefix to externally linked tags

Check this box if you want to insert a prefix in front of the names of linked tags in your Variable.DBF.

Tag prefix

The prefix that will be inserted in front of the names of linked tags in your Variable.DBF (for this I/O Device only). To change the prefix, delete it first, perform a manual refresh, then add the new prefix.

Automatic refresh of tags

Determines whether the linked tags in CitectSCADA's variable tags database will be updated when the external data source is changed (i.e. you manually change a field, etc.). This refresh will occur the first time you link to the data source, and then whenever you attempt to read the changed variables (for example you compile your project, display the variable using the Variable Tags form, or paste the tag, etc.).

Without an automatic refresh, you will need to perform a manual refresh to update the linked tags in CitectSCADA.

Live Update

This field is only available if you have installed one of the CitectSCADAFastLinx products. It controls whether or not the linked tags in CitectSCADA and an external tag database will be synchronized if either database is changed. To enable live linking, choose Yes from the Live Update menu, and verify that the Automatic refresh check box is not selected. (Live Update and Automatic Refresh are mutually exclusive.)

When Live Update is enabled and the CitectSCADA variable tag database is accessed (for example, during project compilation or when a dropdown list is populated), CitectSCADA queries the external tag database to determine if it has been modified. If so, CitectSCADA merges the changes into the local variable tag database. Conversely, any changes made to the local tag variable database will be incorporated seamlessly into the external tag database.

See Also