Generic OPC syntax

An Communication Driver is a container for OPC Groups, providing the mechanism for containing and logically organizing OPC items. Within each OPC Group, an OPC-compliant client can register OPC items, which represent connections to devices in the field device. All access to OPC items is maintained through the OPC Group.

The fully qualified name for an OPC item is the Item ID, equivalent to Item Name. The syntax for specifying a unique Item ID is Communication Driver-dependent. In OPC data acquisition Communication Drivers, the syntax can be as follows:

TCPIP.PLC1.DB1,B20

Where each component (delimited by a period) represents a branch or leaf of the field device’s hierarchy.

In this example:

• PLC1 is the name of the target PLC.

• DB1,B20 is the specific data point or item desired.

An item is typically a single value such as an analog, digital, or string value, where:

• Item ID describes the syntax for defining the data point.

• OPC provides another parameter, called Access Path, that defines optional specifications for obtaining that data.

In Communication Drivers, Access Paths are equivalent to Device Groups. This parameter defines the update interval between the Communication Driver and the field device for accessing the values of data points in the PLC.