WAGO 750-306 Technical Description

Also see for DeviceNet 750-306: Manual

WAGO 750-306 Technical Description Manual pdf 106 page image

106 ï DeviceNetDescriptionWAGO-I/O-SYSTEM 750DeviceNet5 DeviceNet5.1 DescriptionDeviceNet is a networking concept in the device level based on the serial bussystem CAN (Controller Area Network). It is particularly distinguished by theproblem-free addition and removal of devices, from simple light barriers up tocomplex motor controls during operation. DeviceNet is mainly used in indus-trial automation and for robot controls.The Data Link Layer, i.e. the physical and data storage layer, is defined in theCAN specification. The telegram architecture is described. However, there isno information about the application layer.This is where DeviceNet comes into play. It describes the defined meaning ofthe data transmitted in the application layer.The Open DeviceNet Vendor Association (abridged: ODVA) is the user or-ganisation for DeviceNet. In a specification, the ODVA DeviceNet is definedas a uniform application layer and it lays down technical and functional fea-tures for device networking.A maximum of 64 fieldbus nodes can be operated in one DeviceNet network.The extension of the network depends on the selected baud rate (125 kBaud,250 kBaud or 500 kBaud).In contrast to other fieldbus systems, CAN does not address the modules con-nected to the bus but identifies the messages. Whenever the bus is free, sub-scribers are allowed to send messages. Each bus subscriber decides on its ownwhen it wants to send data or instigate other bus subscribers to send data. Thispermits a communication without a bus master assembly group.Bus conflicts are solved in that the messages are assigned a certain priority.This priority is defined by the CAN identifier, called Connection ID in De-viceNet. The following rule applies: the smaller the identifier, the higher thepriority.A general distinction between high priority process messages (I/O Messages)and low priority management messages (Explicit Messages) is done before.Messages having a data length of more than 8 bytes can be fragmented.The communication with DeviceNet occurs always connection-referenced(connection based). All data and functions of a device are described by meansof an object model. Therefore, for a message exchange directly after switchingon a device, the connections to the desired subscriber have to be establishedfirst and communication objects be created or allocated. Message distributionis according to the broadcast system, data exchange according to the producerconsumer model.A transmitting DeviceNet node produces data that is either consumed via apoint-to-point connection (1 to 1) by one receiving node, or via a multicastconnection (1 to n) by several receiving nodes.Further informationThe Open DeviceNet Vendor Association (ODVA) provides further docu-ments in the Internet under: http://www.odva.org