GE Motor Protection System, LM10 A.1.2 Controller Area Network CAN, A.1.3 DeviceNet Operations

DEVICENET OVERVIEW CHAPTER A:

A.1.2 Controller Area Network (CAN)

The Controller Area Network (CAN) is a broadcast-oriented communications protocol. DeviceNet uses CAN for its data link layer. The CAN protocol has a fast response and high reliability for demanding applications such as control of anti-lock brakes and air-bags. Devices are now available for the industrial automation market demanding stability in high temperature and high noise immunity.

A.1.3 DeviceNet Operations

DeviceNet is a connection based protocol; that is, all devices should establish a connection prior to exchanging information. DeviceNet adopts the object modelling approach – all information is structured in different objects. Services (such as Get and Set) can be applied to these objects to extract/change information. The following are the typical object classes found in a DeviceNet product:

1.Identity object. Identification information (such as vendor ID, device profile, revision, etc.) of a device are stored in this object. Users can identify a particular object by remotely access to this object.

2.Message Router object. This object handles the explicit messages received by routing it to the proper destination objects.

3.DeviceNet object. A DeviceNet product will typically have a single instance of the DeviceNet object. This instance would have as attributes: node, address, or MAC ID, baud rate, bus-off action, bus-off counter, allocation choice, and the master MAC ID. The only required service is Get_Attribute_Single.

4.Connection object. This object handles the connection of the module, such as Explicit Messaging or Input/Output Messaging. Explicit messages contain attribute addressing, attribute values and a service code describing the desired action. Input/ output messages contain nothing but data. In an input/output message, all information about how to process the data is contained in the Connection object associated with that I/O message

5.Assembly object(s). A DeviceNet product typically has one or more optional Assembly objects. The primary purpose of these objects is to group different attributes (data) from different application objects into a single Attribute.

6.Parameter object. The optional Parameter object is used in parameter-based devices. One instance would be presented for each configurable parameter. The Parameter object provides a standard method for a configuration tool to access all parameters. Attributes of the Parameter object could include values, ranges, text strings, and limits.

7.Application objects. Usually at least one application object besides those from the Assembly or Parameter class will be present in a device. There are a number of standard objects in the DeviceNet object library.

Each object has its own parameters called attributes (such as vendor ID). The behavior of a device is governed by these attributes.

Once the connection is established, all the data exchanged across this connection are handled by the corresponding connection instance.

A–2 LM10 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL