112 • DeviceNet

Network Communication

5.3 Network Communication

5.3.1 Objects, Classes, Instances and Attributes

Protocol processing of DeviceNet is object oriented. Each node in the network is represented as a collection of objects. In the following, several terms connected with them are defined:

•Object:

Object is an abstract representation of individual components within a device belonging to each other. It is defined by its data or attributes, its external functions or services available, and by its defined behaviour.

•Class:

A class includes objects of a product belonging together, it is organized in instances, e.g. Identity Class, DeviceNet Class.

•Instance:

An instance is composed of various variables (attributes). Differing instances of a class have the same services, the same behaviour and the same variables (attributes). However, they can have different variable values, e.g. different connection instances: Expilict Message, Poll I/O or BitStrobe connection instance.

•Attributes:

The attributes represent data provided by a device via DeviceNet. They contain the current values, e.g. a configuration of an input, such as, for instance Vendor ID, Device Type or Product Name.

•Service:

Services can be applied to classes and attributes. They perform defined actions, e.g. reading of variables (attributes) or resetting a class.

•Behaviour:

The behaviour defines how a device reacts as a consequence of external events, such as changed process data, or as a consequence of internal events, such as expiring timers.

WAGO-I/O-SYSTEM 750

DeviceNet