Structure access (OPC)

Determines how process variables of the data type of a structure definition are accessed.

Setting	Description of the
As bytestream	If a process variable of the data type of a structure is read/written, the data is exchanged as a byte stream between the OPC server and the variable server. VWOPC servers use this data format.
As structure (IEC1131)	If a process variable of the data type of a structure is read/written, the data is exchanged as variant data between the OPC server and the variable server.
As individual variables	During the initialisation phase, each structure element is registered with the OPC server as an individual process variable. Block-by-block access to a process variable of the data type of a structure definition is therefore an access to each structure element in this process variable.

The setting of the structure access parameter depends on the functional scope of the OPC server.

In principle, the following applies:

VWOPC servers use the Bytestream mode.

OPC servers that do not recognise extended data types must be set to the As single variables mode if structure definitions are used in the VisiWin project. Further information can usually be found in the OPC server documentation.

Parameters for module:

• Variables

• Communication channel (OPC)