Beckhoff EtherCAT EL6752, Документация

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Basic DeviceNet principles
EL6752 14 Version: 2.1
3 Basic DeviceNet principles
Introduction to the system
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. CAN’s bit
arbitration procedure makes it theoretically possible to operate communication networks using master/slave
and multimaster access methods.
Further details can be found on the official website of the ODVA (
http://www.odva.org ).
Fig. 10: Example of DeviceNet in use
Bus cable
The bus cable consists of two pairs of shielded twisted-pair wiring, one for the data transfer and one for the
power supply. The latter can carry currents of up to 8 amperes. The maximum possible length of a line
depends essentially on the baud rate. If you choose the highest Baud rate (500 kbaud) you are restricted to
lines of at most 100 m. With the lowest Baud rate (125 kbaud) you will be able to use cable with an overall
length of 500 m. Refer to the chapter "
Mounting and wiring [
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19] " for details
Fig. 11: Example of DeviceNet cabling