DeviceNet
Encyclopedia
DeviceNet is a network system used in the automation industry to interconnect control devices for data exchange. It uses Controller Area Network
as the backbone technology and defines an application layer to cover a range of device profiles. Typical applications include information exchange, safety devices, and large I/O control networks.
(now owned by Rockwell Automation
). It is layered on top of the CAN (Controller Area Network
) technology, developed by Bosch. DeviceNet adapts the technology from ControlNet
, which is another industrial protocol developed by Allen-Bradley
, and takes advantage of CAN, making it low-cost and robust compared to the traditional RS-485 based protocols.
In order to promote the use of DeviceNet worldwide, Rockwell Automation has adopted the "open" concept and decided to share the technology to third party vendors. Hence, it is now managed by the Open DeviceNet Vendors Association
(ODVA), an independent organization located in North America. ODVA maintains specifications of DeviceNet and oversees advances to DeviceNet. In addition, ODVA ensures compliance to DeviceNet standards by providing conformance testing
and vendor conformity.
ODVA later decided to bring DeviceNet back to its predecessor's umbrella and collectively call the technology as Common Industrial Protocol
or (CIP), which includes the following technologies:
ODVA claims high integrity between the three technologies due to the common protocol adaptation, which makes industrial controls much simpler compared to other technologies.
References
Nodes are distributed along a DeviceNet network by the means of a trunkline-dropline topology. This topology allows for ease in wiring and access to the network from multiple taps. In addition, nodes can be easily removed and added to reduce production downtime, increase network flexibility, and decrease troubleshooting time. Since the physical layer is optically isolated from device, communication power and device power can share the same bus (Further reducing the complexity of the network and components within). ( Introduction)
DeviceNet supports 125 kbit/s, 250 kbit/s and 500 kbit/s data rates. Depending on the chosen cable type, DeviceNet can support communication up to 500 meters (Round thick cable). Typical round cable supports up to 100 meters. While flat style cable supports up to 380 meters at 125 kbit/s and 75 meters at 500 kbit/s.( Physical Layer )
Data Link Layer
DeviceNet uses a differential serial bus (Controller Area Network
) as its Data Link Layer. Using CAN as a backbone, DeviceNet requires minimal bandwidth to transmit and package messages. In addition, a smaller processor may be selected in the design of device thanks to data frame format and the ease at which the processor can parse through the data. See below for full format.( The Data Link Layer)
CAN Data Frame Format
1 Bit => Start of Frame
11 Bits => Identifier
1 Bit => RTR Bit
6 Bits => Control Field
0-8 Bytes => Data Field
15 Bits => CRC Sequence
1 Bit => CRC Delimiter
1 Bit => Acknowledge
1 Bit => Ack Delimiter
7 Bits => End of Frame
>2 Bits => Interframe Space
Reference: Table: Data Frame Format.
Upon transmitting the first packet of data, the "Start of Frame" bit is sent to synchronize all receivers on the network. The CAN identifier (denoted from 0-63) and RTR bit combine to set priority at which the data can be accessed or changed. Lower identifiers have priority over higher identifiers. In addition to transmitting this data to other devices, the device also monitors the data sent. This redundancy validates the data transmitted and eliminates simultaneous transmissions. If a node is transmitting at the same time as another node, the node with the lower 11 bit identifier will continue to transmit while the device with the higher 11 bit identifier will stop.(Introduction & Physical Layer.)
The following 6 bits contain information for specifying the Control Field. The initial two bits are fixed, while the last four are used to specify length field of the Data Field. The Data Field contains from zero to eight bytes of usable data.(Physical Layer.)
The following data frame is the CRC (Cyclic Redundancy Check
) Field. The frame consists of 15 bits to detect frame errors and maintains numerous format delimiters. Due to ease of implementation and immunity to most noisy networks, CAN provides a high level of error checking and fault confinement.(Physical Layer.)
Network
DeviceNet incorporates a connection-based network. A connection must initially be established by either an UCMM (Unconnected Message Manager) or a Group 2 Unconnected Port. From there, Explicit and Implicit messages can be sent and received. Explicit messages are packets of data that general require a response from another device. Typical messages are configurations or non-time sensitive data collection. Implicit messages are packets of data that are time critical and generally communicate real-time data over the network. An Explicit Message Connection has to be used to established first before an Implicit Message Connection is made. Once the connection is made, the CAN identifier routes data to the corresponding node.(The Network and Transport Layers.)
A full-test version is called the Composite test. It consists of:
Reference
Notes
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
as the backbone technology and defines an application layer to cover a range of device profiles. Typical applications include information exchange, safety devices, and large I/O control networks.
History
DeviceNet was originally developed by American company Allen-BradleyAllen-Bradley
Allen-Bradley is the brand-name of a line of Factory Automation Equipment manufactured by Rockwell Automation . The company, with revenues of approximately US$4.5 billion in 2006, manufactures programmable automation controllers , human-machine interfaces, sensors, safety components and systems,...
(now owned by Rockwell Automation
Rockwell Automation
Rockwell Automation is a global provider of industrial automation, power, control and information solutions. Brands in industrial automation include Allen-Bradley and Rockwell Software....
). It is layered on top of the CAN (Controller Area Network
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
) technology, developed by Bosch. DeviceNet adapts the technology from ControlNet
ControlNet
-Introduction:ControlNet is an open industrial network protocol for industrial automation applications, also known as a fieldbus. ControlNet was earlier supported by ControlNet International, but in 2008 support and management of ControlNet was transferred to ODVA, which now manages all protocols...
, which is another industrial protocol developed by Allen-Bradley
Allen-Bradley
Allen-Bradley is the brand-name of a line of Factory Automation Equipment manufactured by Rockwell Automation . The company, with revenues of approximately US$4.5 billion in 2006, manufactures programmable automation controllers , human-machine interfaces, sensors, safety components and systems,...
, and takes advantage of CAN, making it low-cost and robust compared to the traditional RS-485 based protocols.
In order to promote the use of DeviceNet worldwide, Rockwell Automation has adopted the "open" concept and decided to share the technology to third party vendors. Hence, it is now managed by the Open DeviceNet Vendors Association
Open DeviceNet Vendors Association
Open DeviceNet Vendors Association is an international organization that supports computing network technologies based upon the Common Industrial Protocol . These include DeviceNet, EtherNet/IP, CIP Safety and CIP Sync. Members of ODVA include representatives of leading automation companies...
(ODVA), an independent organization located in North America. ODVA maintains specifications of DeviceNet and oversees advances to DeviceNet. In addition, ODVA ensures compliance to DeviceNet standards by providing conformance testing
Conformance testing
Conformance testing or type testing is testing to determine whether a product or system meets some specified standard that has been developed for efficiency or interoperability....
and vendor conformity.
ODVA later decided to bring DeviceNet back to its predecessor's umbrella and collectively call the technology as Common Industrial Protocol
Common Industrial Protocol
The Common Industrial Protocol is an industrial protocol for industrial automation applications. It is supported by ODVA.Previously known as Control and Information Protocol, CIP encompasses a comprehensive suite of messages and services for the collection of manufacturing automation applications...
or (CIP), which includes the following technologies:
- EtherNet/IPEtherNet/IPEtherNet/IP is a communications protocol developed by Rockwell Automation, managed by the Open DeviceNet Vendors Association and designed for use in process control and other industrial automation applications....
(take note of the capital 'N', and "IP" here means "Industrial Protocol") - ControlNetControlNet-Introduction:ControlNet is an open industrial network protocol for industrial automation applications, also known as a fieldbus. ControlNet was earlier supported by ControlNet International, but in 2008 support and management of ControlNet was transferred to ODVA, which now manages all protocols...
- DeviceNet
- CompoNet
ODVA claims high integrity between the three technologies due to the common protocol adaptation, which makes industrial controls much simpler compared to other technologies.
Technical Snapshot
- Defines the Media, Physical, Data-Link, and Application layers of the ISO/OSI 7-layer model (see Open Systems InterconnectionOpen Systems InterconnectionOpen Systems Interconnection is an effort to standardize networking that was started in 1977 by the International Organization for Standardization , along with the ITU-T.-History:...
) - Incorporates trunkline topology with separate buses for signal and power (Typical configuration: two twisted pairs and a single shield)
- Baudrates defined: 125 kbit/s, 250 kbit/s, and 500 kbit/s
- Trunk length is inversely proportional to the speed, i.e. 500, 250 and 100 meters respectively
- A not-so new flat cable was added to the specification to allow the use of the quick-fix connector
- Up to 64 nodes on a single logical network. (Node addresses range from 0 - 63) The network has a low node priority scheme
- Supports master/slave as well as peer-to-peer communication, although majority of the devices work in the master/slave configuration
- Allows multiple masters on a single logical network
- Network cable can supply device power along same cable as communication cable (Generally smaller devices such as photo-eyes, limit switches, and proximity switches).
- Networked devices can be simultaneously controlled and configured
- Engineered to withstand noisy environments
- Supports 4 message types to/from slave devices (Strobed, Polled, Cyclic, COS (change of state)). Some devices support more than 1 message type
References
Architecture
Physical LayerNodes are distributed along a DeviceNet network by the means of a trunkline-dropline topology. This topology allows for ease in wiring and access to the network from multiple taps. In addition, nodes can be easily removed and added to reduce production downtime, increase network flexibility, and decrease troubleshooting time. Since the physical layer is optically isolated from device, communication power and device power can share the same bus (Further reducing the complexity of the network and components within). ( Introduction)
DeviceNet supports 125 kbit/s, 250 kbit/s and 500 kbit/s data rates. Depending on the chosen cable type, DeviceNet can support communication up to 500 meters (Round thick cable). Typical round cable supports up to 100 meters. While flat style cable supports up to 380 meters at 125 kbit/s and 75 meters at 500 kbit/s.( Physical Layer )
Data Link Layer
DeviceNet uses a differential serial bus (Controller Area Network
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
) as its Data Link Layer. Using CAN as a backbone, DeviceNet requires minimal bandwidth to transmit and package messages. In addition, a smaller processor may be selected in the design of device thanks to data frame format and the ease at which the processor can parse through the data. See below for full format.( The Data Link Layer)
CAN Data Frame Format
1 Bit => Start of Frame
11 Bits => Identifier
1 Bit => RTR Bit
6 Bits => Control Field
0-8 Bytes => Data Field
15 Bits => CRC Sequence
1 Bit => CRC Delimiter
1 Bit => Acknowledge
1 Bit => Ack Delimiter
7 Bits => End of Frame
>2 Bits => Interframe Space
Reference: Table: Data Frame Format.
Upon transmitting the first packet of data, the "Start of Frame" bit is sent to synchronize all receivers on the network. The CAN identifier (denoted from 0-63) and RTR bit combine to set priority at which the data can be accessed or changed. Lower identifiers have priority over higher identifiers. In addition to transmitting this data to other devices, the device also monitors the data sent. This redundancy validates the data transmitted and eliminates simultaneous transmissions. If a node is transmitting at the same time as another node, the node with the lower 11 bit identifier will continue to transmit while the device with the higher 11 bit identifier will stop.(Introduction & Physical Layer.)
The following 6 bits contain information for specifying the Control Field. The initial two bits are fixed, while the last four are used to specify length field of the Data Field. The Data Field contains from zero to eight bytes of usable data.(Physical Layer.)
The following data frame is the CRC (Cyclic Redundancy Check
Cyclic redundancy check
A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
) Field. The frame consists of 15 bits to detect frame errors and maintains numerous format delimiters. Due to ease of implementation and immunity to most noisy networks, CAN provides a high level of error checking and fault confinement.(Physical Layer.)
Network
DeviceNet incorporates a connection-based network. A connection must initially be established by either an UCMM (Unconnected Message Manager) or a Group 2 Unconnected Port. From there, Explicit and Implicit messages can be sent and received. Explicit messages are packets of data that general require a response from another device. Typical messages are configurations or non-time sensitive data collection. Implicit messages are packets of data that are time critical and generally communicate real-time data over the network. An Explicit Message Connection has to be used to established first before an Implicit Message Connection is made. Once the connection is made, the CAN identifier routes data to the corresponding node.(The Network and Transport Layers.)
Conformance Test
To declare your product as DeviceNet compatible, a vendor needs to send their product to the ODVA test lab for the certification. ODVA used to have a few other test labs around the world, i.e. UK, Japan, and China. It has since been consolidated into one facility in North America.A full-test version is called the Composite test. It consists of:
- Conformance test. Test against the protocol specification.
- Interoperability test. Test against devices from various vendors on a single, fully populated, network.
Conformance Test Procedure
The following procedure shows you how to get your product certified.- Register as vendor with ODVA. You will be given a vendor ID.
- Purchase a copy of the DeviceNet specification. A hard and soft copy will be sent to you.
- Purchase the conformance test software and corresponding hardware interface card. Note that only selected interface cards from a few vendors can be used.
- Develop and test product in-house. You would probably need help from the discussion group, see the External links below.
- Submit your product to ODVA test lab for independent verification.
- Repeat the above two steps until your product successfully pass the independent test.
Reference
Sources
Notes