Find and Connect to OPC HDA Server

Prerequisites

To interact with an OPC HDA server, you must provide:

The host name of the computer on which the OPC HDA server is installed. Typically the host name is a descriptive term (such as 'plantserver') or an IP address (such as 192.168.2.205).
The server ID of the server you want to access on that host. Because a single computer can host multiple OPC HDA servers, each server installed on that computer is given a unique ID during installation.

Your network administrator can provide the host names for all computers with OPC HDA servers on your network. You can also obtain a list of server IDs for each host on your network, or use the opchdaserverinfo function to access server IDs from a host.

Determine HDA Server IDs for a Host

When an OPC server is installed, it must be assigned a unique server ID. This server ID provides a unique name for a particular instance of an OPC server on a host, even if multiple copies of the same server software are installed on that same machine.

To determine the server IDs of the OPC servers installed on a host, call the opchdaserverinfo function, specifying the host name as the only argument.

info = opchdaserverinfo('localhost')

When called with this syntax, the function returns a structure containing information about all the OPC servers available on that host.

info = 
1x4 OPC HDA ServerInfo array:
    index    Host                 ServerID               HDASpecification                    Description                   
    -----  ---------  ---------------------------------  ----------------  ------------------------------------------------
      1    localhost  Advosol.HDA.Test.3                 HDA1              Advosol HDA Test Server V3.0
      2    localhost  IntegrationObjects.OPCSimulator.1  HDA1              Integration Objects OPC DX HDA Simulator 2
      3    localhost  IntegrationObjects.OPCSimulator.1  HDA1              Integration Objects' OPC HDA Server Simulator
      4    localhost  Matrikon.OPC.Simulation.1          HDA1              MatrikonOPC Server for Simulation and Testing

The fields in the structure provide information listed in this table.

Server Information Returned by opchdaserverinfo

Field	Description
`Host`	Character vector that identifies the name of the host. No name resolution is performed on an IP address.
`ServerID`	Cell array containing the server IDs of all OPC servers accessible from that host.
`HDASpecification`	Cell array containing the OPC specification that the server provides.
`Description`	Cell array containing descriptive text for each server.

You can examine the returned structure for specific details using the field name. For example, to query for the server IDs of each OPC server use this syntax.

allServers = {hostInfo.ServerID}

allServers =
Columns 1 through 3
	'Advosol.HDA.Test.3'    'IntegrationObjects.OPCSimulator.1'    'IntegrationObjects.OPCSimulator.1'
Column 4
	'Matrikon.OPC.Simulation.1'

Create OPC HDA Client Object

After determining the host name and server ID of the OPC HDA server you want to connect to, you can create an OPC HDA client object. The client controls the connection status to the server, stores properties of that server, and allows you to read data from the server.

Create an OPC HDA client using the opchda function and specifying the host name and server ID arguments.

hdaClient = opchda('localhost', 'Matrikon.OPC.Simulation.1')

hdaClient =
OPC HDA Client localhost/Matrikon.OPC.Simulation.1:
	Host: localhost
	ServerID: Matrikon.OPC.Simulation.1
	Timeout: 10 seconds

	Status: disconnected

	Aggregates: -- (client is disconnected)
	ItemAttributes: -- (client is disconnected)

You can also construct client objects directly from an OPC HDA ServerInfo object using this code.

hostInfo = opchdaserverinfo('localhost');
hdaClient = opchda(hostInfo(1));

Set Client Properties

You can modify many properties specific to the created client. These include Timeout, UserData, Host (before connection), and ServerID (before connection). Modify these properties as you would any other field of a MATLAB^® structure.

Set Timeout Property

As OPC transactions often occur across networks, you might encounter cases where calls to those servers take some time to return. To change the function timeout of the OPC HDA client object, assign a new value to its Timeout property.

hdaClient.Timeout = 12

hdaClient = 
OPC HDA Client localhost/Matrikon.OPC.Simulation.1:
               Host: localhost
           ServerID: Matrikon.OPC.Simulation.1
           Timeout: 12 seconds

             Status: connected

         Aggregates: 6 Aggregate Types
     ItemAttributes: 10 Item Attributes
Methods

Connect to OPC HDA Server

OPC HDA client objects do not automatically connect to the server once you create them. You can see this from the Status property of the client object.

Use the connect function to connect an OPC HDA client object to the server at the command line.

connect(hdaClient)

After connecting the client to the server, call the client object to view the updated properties.

hdaClient

hdaClient = 
OPC HDA Client localhost/Matrikon.OPC.Simulation.1:
               Host: localhost
           ServerID: Matrikon.OPC.Simulation.1
            Timeout: 10 seconds

             Status: connected

         Aggregates: 6 Aggregate Types
     ItemAttributes: 10 Item Attributes

Browse OPC Server Namespace

Use the client object connected to the server to obtain information about the namespace of that server. The server namespace provides access to all the data points provided by the OPC server by naming each data point and arranging them into a namespace that provides a unique identifier for each server item. See Retrieve OPC HDA Server Namespace. You can also graphically browse the HDA server namespace using the browseNamespace function.

Read Item Attributes

Each item that you find on a server might have a given set of item attributes associated with it. These attributes provide information about the item stored on the server. The OPC Foundation defines a set of common item attributes, while specific servers can define server-specific attributes. However, support for item attributes is optional for any server.

You can find the attributes supported by your server by querying the ItemAttributes property of a connected HDA client object:

hdaClient.ItemAttributes

OPC HDA Item Attributes:
         Name           ID        Description   
    --------------  ----------  ----------------
    DATA_TYPE           1       Data type
    DESCRIPTION         2       Item Description
    NORMAL_MAXIMUM      11      High EU
    NORMAL_MINIMUM      12      Low EU
    ITEMID              13      Item ID
    TRIANGLE        4294967291  Triangle Wave
    SQUARE          4294967292  Square Wave
    SAWTOOTH        4294967293  Saw-toothed Wave
    RANDOM          4294967294  Random
    BUCKET          4294967295  Bucket Brigade

Use the readItemAttributes function to retrieve the item attributes for a particular item.

For a list of item attributes defined by the OPC Foundation for the OPC HDA specification, see OPC HDA Item Attributes.