Материал: m013500e_x06

DeviceNet • 111

Network Architecture

WAGO Kontakttechnik GmbH has developed a Multi-Port DeviceNet Tap to connect the nodes to permit the connection of remote bus cables and drop lines using the CAGE CLAMP® technology. This achieves a reliable, fast and vibration and corrosion resistant connection.

The DeviceNet taps are available in 2 designs.

All subscribers in the network communicate at the same Baud rate. The bus structure permits the interference-free connection and disconnection of stations or a stepped start-up of the system.

Future extensions have no influence on the stations already in operation. Should a subscriber fail or be added to the network as a new one, it is automatically deteced by the system.

5.2.4 Network Grounding

The devices can either be power supplied via the DevicNet bus or have their own power supply.

Prerequisite being, however, that the network is only grounded at one point. Preferably, grounding is in the network center (V and screen drain with round media) to optimize the capacity and minimize interference.

Not permitted are ground loops via devices that are not disconnected from the power supply. The device must either be insulated or, if this is not possible, the power must be correspondingly disconnected in the device.

5.2.5 Interface Modules

In a network, all WAGO DeviceNet fieldbus nodes are delivered to operate as slaves. The master operation is taken over by a central control system, such as PLC, NC or RC.

Note

The programmable fieldbus Controller 750-806 can assume the master operation when being extended by the "DevNet.lib" library.

The connection to fieldbus devices is made via interface modules.

As an interface module, WAGO offers the PC interface PCBs for DeviceNet, ISA DeviceNet Master 7KByte (order No. 758-340), PC104 DeviceNet Master 7KByte D-Sub,straight, angled (order No. 758-341) and PCI DeviceNet Master 7 Kbyte (order No. 758-342) from the WAGO-I/O-SYSTEM 758 Series.

Other interface modules for programmable logic controls (PLCs) are also offered by other manufacturers.

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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.

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DeviceNet • 113

Module Characteristics

5.4 Module Characteristics

The I/O module is defined by vendor ID and device type.

5.4.1 Communication Model

5.4.1.1 Message Groups

CAN messages are divided into several groups in order to achieve different priorities.

•message group 1 serves to exchange I/O data via I/O messages

•message group 2 is reserved for Master/Slave applications

•message group 3 serves to exchange configurations data via explicit messages

•message group 4 is reserved for system administration (i. e. Offline Connection Set)

The CAN Identifier (Connection ID) and with it the priority is built via different message groups and the MAC ID.

5.4.1.2 Message Types

DeviceNet has 2 types of messages:

•I/O Messages and

•Explicite Messages

5.4.1.2.1I/O Messaging

I/O messages are sent by a node and can be received by one or several other nodes. Only I/O data is transmitted and no protocol data is specified by this way.

5.4.1.2.2 Explicit Messaging

Explicit messages are sent directly from one node to another. They consist of a request and an answer. Therefore services can be requested directly from another node. The data field consists of the service identification and the destination address. The format of the explicit messages is defined. Via explicit messages devices can be configured or a dynamic built-up of message connections can be made.

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Process data and Diagnostic Status

5.4.2 I/O Messaging Connections

The transfer or exchange of process data between the scanner and the I/O device is made via a „Polled I/O Connection“, „Change of State/Cyclic“ or „Bit Strobe“.

5.5 Process data and Diagnostic Status

The data is transmitted between master and slave in the form of objects, a differentiation being made between input and output objects. The object architecture is defined by assembly objects which serve to group attributes of differing application objects. I/O data of different objects can, for this reason, be grouped to form a data block and transmitted by a message connection.

5.5.1 Process Image

The process image is differentiated according to input and output process images. The assembly object makes a statically configured process image available in the instances 1 ... 9.

The desired process image can be selected by setting the Produced Connection Path and the Consumed Connection Path of the individual I/O connections (Poll, Bit Strobe, Change of State or Change of Value).

The architecture of the individual instances of the assembly object is described in the following.

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Process data and Diagnostic Status

5.5.1.1 Assembly Instances

Permanently pre-programmed (static) assemblies in the device permit an easy and rapid transmission of input and output images from the fieldbus Coupler/Controller to the master. For this purpose, various assembly instances are provided in the fieldbus Coupler/Controller:

Output 1 (I/O Assembly Instance 1):

The entire output data image is transmitted from the master to the Controller via the corresponding I/O message connection. In this case, the data length corresponds to the number of output data in bytes. Analog output data come before digital output data.

Output 2 (I/O Assembly Instance 2):

The digital output data image is transmitted from the master to the Controller via the corresponding I/O message connection. The data length is equivalent to the number of digital output data and is rounded up to full bytes.

Output 3 (I/O Assembly Instance 3):

The analog output data image is transmitted from the master to the Controller via the corresponding I/O message connection. The data length is equivalent to the number of analog output data in bytes.

Input 1 (I/O Assembly Instance 4):

The entire input data image and one status byte are transmitted to the master via the corresponding I/O message connection. The data length is equivalent to the number of input data in bytes and one status byte.

Input 2 (I/O Assembly Instance 5):

The digital input data image and one status byte are transmitted to the master via the corresponding I/O message connection. The data length is equivalent to the number of digital input data and rounded up to full bytes. In addition, a status byte is inserted.

Input 3 (I/O Assembly Instance 6):

The analog input data image and one status byte are transmitted to the master via the corresponding I/O message connection. The data length is equivalent to the number of analog input data in bytes and one status byte.

Input 1 (I/O Assembly Instance 7):

The entire input data image is transmitted to the master via the corresponding I/O message connection. The data length is equivalent to the number of input data in byte.

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