Specifications

RSLinx – Training Guide B - 13
This specification describes the OPC COM Objects and their interfaces implemented by
OPC Servers. An OPC Client can connect to OPC Servers provided by one or more
vendors.
OPC Client
OPC
Server
Vendor A
OPC
Server
Vendor C
OPC
Server
Vendor B
Figure 0-1 OPC Client
OPC Servers may be provided by different vendors. Vendor supplied code determines the
devices and data to which each server has access, the data names, and the details about how
the server physically accesses that data.
OPC Client #1
OPC
Server
Vendor A
OPC
Server
Vendor C
OPC
Server
Vendor B
OPC Client #2
OPC Client #3
Figure 0-2 OPC Client/Server Relationship
OPC DataAccess Overview
At a high level, an OPC DataAccess Server is comprised of several objects: the server, the
group, and the item. The OPC server object maintains information about the server and
serves as a container for OPC group objects. The OPC group object maintains information
about itself and provides the mechanism for containing and logically organizing OPC
items.
The OPC Groups provide a way for clients to organize data. For example, the group might
represent items in a particular operator display or report. Data can be read and written.
Exception based connections can also be created between the client and the items in the
group and can be enabled and disabled as needed. An OPC client can configure the rate
that an OPC server should provide the data changes to the OPC client.