174 • Ethernet/IP (Ethernet/Industrial Protocol)

Object model

7.3 Object model

7.3.1 General

For network communication, Ethernet/IP uses an object model, in which are described all of the functions and data of a device.

Each node in the network is represented as a collection of objects.

A number of terms relating to object models are defined below:

•Object:

The object model consists of classes of objects. An object is an abstract representation of individual related components within a device. It is defined by its data or attributes, the functions or services it provides externally and by its defined behaviour.

•Class:

A class contains related components (objects) of a product, organized in instances.

•Instance:

An instance consists of different variables (attributes) that describe the properties of this instance. Different instances of a class have the same services, the same behaviour and the same variables (attributes).

They can, however, have different variable values.

•Variable (attribute):

The variables (attributes) represent the data a device provides over Ethernet/IP. These include the current values of, for example, a configuration or an input. Typical attributes are configuration or status information.

•Service:

Services are used to access classes or the attributes of a class or to generate specific events. These services execute defined actions such as the reading of variables or the resetting of a class. For each class, there exists a fixed set of services.

•Behaviour:

The behaviour defines how a device reacts as a result of external events such as changed process data or internal events such as lapsing timers.

WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP