Accessing the Data in Your DAServer

The method for accessing items through the DAServer depends on the communications protocol being used.

In the case of OPC communications, the protocol addresses an element of data in a conversation with six characteristics: node name, program name, group name, device group, link name, and item name.

• The node name (required for remote access) and device group are optional.

• A fully qualified OPC Item name (ItemID) is composed of the link name and item name.

• All other characteristics are specified through separate DAServer means.

To access an OPC item, the OPC client needs to connect to the DAServer (out-of-process) and create an OPC group defining the data-acquisition properties for the collection of items to be added. OPC groups can be either public or private. Public OPC groups are shared across multiple clients, whereas private OPC groups are local to a single client. Optionally a device group, which indicates the access path to the items for read/write, can be specified from the DAServer.

The following briefly describes each characteristic of the OPC protocol:

• node name: Computer (host) name identifying a specific node on the network (for Remote Access ONLY).

• program name: The registered OPC server name uniquely identifying a specific server (ProgID). For this DAServer, the program name is ArchestrA.DASABTCP.3.

• group name: The OPC group created from the client for organizing a collection of items logically with the same data acquisition properties between the client and the server, such as update rate.

• device group: Meaningful names configured in the DAServer under a specific controller for the common custom attributes between the DAServer and the device, such as update interval. If not specified from the client, the default device group using the global configuration attribute values from the DAServer is assumed. Functionally a device group is equivalent to an access path (optional).

• link name: The set of hierarchy node names, representing the specific devices on a communications path link from the hierarchy root to a specific controller as configured for this DAServer under the DAServer Manager, separated by delimiters.

• item name: A specific data element, the leaf of the hierarchy tree of this DAServer, within the specified group. For example, when using this DAServer, an item can be a relay, timer, counter, register, and so on, in the controller.

In the case of DDE/SuiteLink communications, the protocol addresses an element of data in a conversation that uses a four-part naming convention that includes the node name, application name, topic name, and item name. The fully qualified DDE/SuiteLink naming convention includes all four parts, although the node name part (required for remote access only) is optional. The following briefly describes each portion of this naming convention:

• node name: Computer (host) name identifying a specific node on the network (for Remote Access ONLY).

• application name: The name of the Windows program (this DAServer) that will be accessing the data element. In the case of data coming from or going to Allen-Bradley devices via the DDE/SuiteLink PlugIn of this DAServer, the application name portion of the address is DASABTCP.

• topic name: Meaningful names are configured in the DAServer to identify specific devices. These names are then used as the topic names in all conversations with that device. For example, ABPLC. Topic name maps to a device group defined in the DAServer.

  Note: You can define multiple device-group (topic) names for the same device (PLC) to poll different points at different rates.

• item name: A specific data element within the specified topic. For example, when using this DAServer, an item can be a relay, timer, counter, register, and so on, in the PLC.

  Note: The term "point" is used interchangeably with the term "item" in this user's guide.

For more information on item/point names, see the Item Names section of this user's guide.