148 • EtherNet/IP (Ethernet/Industrial Protocol)Object modelWAGO-I/O-SYSTEM 750ETHERNET TCP/IP4.3.3 Object model4.3.3.1 GeneralFor network communication, EtherNet/IP uses an object model, in which aredescribed 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 abstractrepresentation of individual related components within a device. It isdefined by its data or attributes, the functions or services it providesexternally and by its defined behaviour.• Class:A class contains related components (objects) of a product, organized ininstances.• Instance:An instance consists of different variables (attributes) that describe theproperties of this instance. Different instances of a class have the sameservices, 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 overEtherNet/IP. These include the current values of, for example, aconfiguration or an input. Typical attributes are configuration or statusinformation.• Service:Services are used to access classes or the attributes of a class or togenerate specific events. These services execute defined actions such asthe reading of variables or the resetting of a class. For each class, thereexists a fixed set of services.• Behaviour:The behaviour defines how a device reacts as a result of external eventssuch as changed process data or internal events such as lapsing timers.
