OPC Group

OPC Group objects are containers of OPC Item objects. They define some characteristics of a group of items like:

Update rate

Active state

Deadband

Communication type

Share type

The update rate of an OPC Group informs how much time is between two reads of a group from the server.

The active state indicates if a group is active or not.

The deadband helps to define how much time exists between a call from server to client.

Four communication type are allowed: synchronous, asynchronous, refresh and subscription. On the synchronous read, the client calls

the server for a value and wait for it. This method is recommended to data process obtained fastly. Slowly obtained data process can do

the system be slow. On the asynchronous read, the client calls the server for a value and do not wait for it because the response can delay.

When the refresh is selected, the client reads all active items in active groups. With the subscription communication type activated, the

server read all items and send only the modified one.

The data can be obtained from two different ways: from cache or from device. On the first one, the data is read from a cache on the server.

On he second one, the data is obtained directly from the device.

A group can be shared in two different ways: public or local. Public groups can be accessed from multiple clients, while local groups can be

accessed only from local clients.