Manage device items

Device Items are used to access data in the Communication Driver and the connected devices. The device item name is an alternative name for the item reference. It is an “alias” or a label for the data in the device. You can use this label instead of the item reference when you create the client application. Defining device items provides a more user-friendly way to name data in the device. Defining device items is optional.

Device items consist of two pieces: a name and an item reference. Once defined, you can access it in the client program either through item name or the item reference. The item reference identifies data in the device. The item reference is a PLC memory reference. Each device’s memory reference can have a different format. For more information, see your Communication Driver-specific documentation.

The actual item reference can be entered as the device item name. In this case, the item reference value can be left empty.

To provide diagnostic and operational information, there are several system items that do not access data in a device. They are grouped by function:

• Global system items

• Device-group-specific system items

• Device-specific system items

For more information about system items, see Standard system items.

The defined device item names show up as OPC browsable items. While the Communication Driver is active, you can add and make changes to the device items. Changes take effect immediately, and the new items are immediately available to client applications. OPC clients that are already connected to the item are not affected until they release and re-acquire the item.

For detailed formats for specifying item references and how to subscribe to data items, see your Communication Driver-specific documentation.