Basic Function Principles
BK52x0 and LC5200 15Version: 2.0.0
3.3 DeviceNet
3.3.1 DeviceNet Introduction
Fig.5: DeviceNet
DeviceNet is an open system based on CAN. CAN was developed some years ago by R. Bosch for data
transmission in motor vehicles. Millions of CAN chips are now in use. A disadvantage for application in
automation is that CAN does not contain definitions for the application layer. CAN only defines the physical
and data link layer.
DeviceNet specifies a uniform application layer and this makes it possible to use the CAN protocol for
industrial applications. ODVA (the Open DeviceNet Vendor Association) is an independent association which
supports manufacturers and users of the DeviceNet system. ODVA ensures that all devices which conform
to the specification can operate together in one system, regardless of their manufacturer.
Fig.6: Example of DeviceNet in use
DeviceNet is a sensor/actuator bus system. It is internationally standardised (EN50325) and is based on
CAN (Controller Area Network). DeviceNet supports a number of communication types for the input and
output data:
• Polling: The master module ("scanner") sends the output data cyclically to the assigned devices and
receives the input data in an answer telegram.
• Change-of-State: Telegrams are sent as soon as their contents have changed.
• Cyclic: The modules send the data automatically after a cycle time has elapsed.
• Strobed: The scanner requests the input data using a broadcast telegram to all the devices.
The DeviceNet devices support all I/O communication types.
The DeviceNet devices are parameterized via acyclical services (explicit messaging).
The effective utilization of the bus bandwidth allows DeviceNet, particularly in Change-of-State mode, to
achieve short system reaction times in spite of the relatively low data rates. The BECKHOFF DeviceNet
devices have a powerful implementation of the protocol. Through active participation in the ODVA's technical
committees, BECKHOFF are contributing to the further development of this bus system, and has in this way
itself gathered profound DeviceNet expertise.
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