CAN/EtherNet

Research Centre

                                           CERC Home

Home ] news ] Composite Test ] Services ] Publications ] Web Links ] Downloads ] F.A.Q. ] DeviceNet UK ]

View our Assembly Cell Live!

Further technical information of DeviceNet can be obtained from the following sites:
  1. DeviceNet Technical Overview By ODVA.
  2. Key Technical Paper By ODVA.
  3. Dr. DeviceNet By ODVA.

DeviceNet FAQ

  1. What is DeviceNet?
  2. Who developed DeviceNet?
  3. How does DeviceNet work?
  4. What is Explicit Messaging and I/O Messaging?
  5. What are the features of DeviceNet?
  6. What are the maximum cable lengths of DeviceNet?
  7. What are the considerations of DeviceNet cable installation?
  8. What is UCMM Capable and UCMM Incapable device?
  9. What CAN transceivers are compliance with DeviceNet?

What is DeviceNet?

DeviceNet is an open low-cost communications link based on the reliable CAN technology to interconnect industrial devices (such as limit switches, photoelectric sensors, valve manifolds, motor starter, process sensors, panel displays, operator interfaces, etc.) via a single network. This eliminate expensive wiring and failure due to the increase of number of connections. It also reduces the cost and time to wire and install industrial automation devices while providing reliable interchangeability of components from multiple vendors. The direct connectivity provides improved communication between devices as well as important device-level diagnostics not easily accessible or available through hardwired I/O interfaces. This technology is used extensively in the U.S., Australia, New Zealand, Japan, China, and it is rapidly gaining popularity in the European region.

DeviceNet is based on the ISO standard for automotive networking known as Controller Area Networking (CAN), which is used in virtually all industries, e.g. automotive, manufacturing, agricultural, medical, building controls, marine, aerospace, etc.

DeviceNet is now an official CENELEC standard - EN50325.

Who developed DeviceNet?

The ODVA is an independent supplier organisation which manages the DeviceNet specification and supports the worldwide growth of DeviceNet. ODVA works with vendors and provides assistance through developer tools, developer training, compliance testing and marketing activities. It has an international membership of more than 300 companies. ODVA publishes the DeviceNet product catalog and supports vendor Special Interest Groups (SIGs) in developing Device Profiles for specific classes of products. The Warwick Manufacturing Group is a member of the ODVA, as well as a participant in the Conformance SIG. ODVA is American based, and it has expanded its base in Europe through the WMG's CAN Lab, which effectively now contains ODVA Europe. Another laboratory has been established at ASTEM RI (Advanced SofTwarE and Mechatronics Research Institute) of Kyoto, Japan.

How does DeviceNet work?

DeviceNet is a connection based protocol, i.e. all devices are required establish a connection prior to exchanging information.

DeviceNet adopts the so-called object modelling approach, i.e. each of the information are structured in different objects. Services (such as Get and Set) can be applied to these objects to extract/change these information. Four basic objects are required to handle these information exchange:

  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. This object handles the explicit messages received by routing it to the proper destination objects.
  3. DeviceNet Object. This object stores all DeviceNet related information, e.g. MAC ID and baud rate.
  4. Connection Object. This object handles the connection of the module, such as Explicit Messaging or I/O Messaging.

Each object has its own parameters called attributes (such as vendor ID). These attributes govern the behaviour of a device.

When a connection has been established, all data exchanged across this connection will be handled by the corresponding connection instance.

What is Explicit Messaging and I/O Messaging?

Explicit Message is the message that contains information (vendors, parameters, etc.) of a module. This information is comparatively less important than the I/O message, therefore it is sent via higher CAN identifier (600-7BF Hex) so that it would not disturb the exchange of I/O message on the bus.

I/O Message is the message that contains real-time I/O information of a module. In order to achieve "real time", these message must be sent as quick as possible, therefore it is sent via lower CAN identifier (000-3FF Hex) than the explicit message.

What are the features of DeviceNet?

DeviceNet's features include:

  1. Low Cost (Based on low cost CAN chip).
  2. High Speed. It supports 3 baud rates: 125Kbps, 250Kbps and 500 Kbps which is believed to meet 95% of the industrial requirement.
  3. Reliable. It uses the well proven CAN protocol incinerates with the application layers that has undergone strict conformance testing to ensure the reliability.
  4. Support up to 64 active nodes. In theory, the node can be expended by using bridge system (such as CAN/CAN bridge or other gateway).
  5. Easy installation. Virtually "Plug-and-Play".

What are the maximum cable lengths of DeviceNet?

DeviceNet defines the maximum cable lengths (trunk and drop cables) to ensure the propagation of the transmitted message falls within the acceptable region. The upper boundaries of the trunk cable and drop cable length are listed as below:

Baud Rate 100% Thick Cable 100% Thin Cable Flat Cable
125 Kbps 500 metres 100 metres 420 metres
250 Kbps 250 metres 100 metres 200 metres
500 Kbps 100 metres 100 metres 100 metres

Trunk cable length specification

Baud Rate Maximum Cumulative
125 Kbps 6 meters 156 meters
250 Kbps 6 meters 78 meters
500 Kbps 6 meters 39 meters

Drop cable length specification

What are the considerations of DeviceNet cable installation?

To install the trunk and drop cable, several considerations have to be taken into account.

  1. If the distance from a trunk line tap to the farthest device connected to it is greater than the distance from the tap to the nearest terminating resistor, then the drop line length must be included as part of the trunk cable length, as well as the drop length calculation.

  2. The cumulative drop line length refers to the sum of all drop lines, thick or thin cable, in the cable system. This sum cannot exceed the maximum cumulative length allowed for the given communication rate used.

What is UCMM capable and UCMM Incapable device?

UCMM (UnConnected Message Manager) capable devices are devices which is capable to exchange data in the peer-to-peer mode. In another word, a device can have different connections with different devices at the same time.

UCMM Incapable devices are devices which is not capable to operate in peer-to-peer mode (see above). These devices are normally referred to as "Group 2 Only server" or "Group 2 Only slave". These devices cannot have connections with more one (master) device. In another word, it can be owned (allocated, or connected) by one and only one master at a time, and any information exchanged are solely between the device and its master only. The master will proxy the slave to respond to requests from other devices, if necessary.

What CAN transceivers are compliance With DeviceNet?

The following lists down the suppliers for the DeviceNet approved CAN transceivers.

Description Manufacturer
82C250/82C251 Philips Semiconductors
UN5350
UN5351 (not released)
Texas Instrument (Unitrode)


However, although it is not stated in the DeviceNet specification, the vendors are advised to use the CAN transceiver that provides over voltage protection of more than 25 voltages (UC5350 and 82C251). The reason DeviceNet specifies the sustain-voltage of CAN transceivers to be 18 volts is due to the fact that the first CAN transceiver available from Philips Semiconductors (82C251) has over-voltage protection of up to 18 volts only.

 

 

Home ] Up ]

Send mail to e.dsouza@warwick.ac.uk with questions or comments about this web site.
Copyright 2000 CAN/EtherNet Research Centre (CERC)
Last modified: 25 April, 2000 12:31 +0100