DeviceNet tutorial
Technical Overview
Behind each and every benefit realized in a new
control system is a significant software
engineering investment designed to deliver
increased productivity through improved
process control and information flow. By
choosing DeviceNet™ products from ODVA’s
member companies, users can protect this
investment in several ways.
First, DeviceNet is a proven, stable network
technology designed to meet the performance
and reliability requirements of the industrial
environment. DeviceNet uses CAN (Controller
Area Network) for its data link layer, and CIP™
(Common Industrial Protocol) for the upperlayers of the network, DeviceNet is an open
standard managed by ODVA and accepted by
international standards bodies around the world.
In addition, users will appreciate the seamless
bridging and routing provided by DeviceNet to
other CIP-based networks which currently
include EtherNet/IP™ and ControlNet™.
Second, DeviceNet is supported by vendors
around the world. Over 700 Vendor IDs have
been issued by ODVA. The fact that so many
vendors have chosen to implement DeviceNet in
their products allows users to employ best-inclass products from vendors around the world
who are best suited to support them based on
application expertise and geographic coverage.
Third, DeviceNet CONFORMANCE TESTED®
products have been certified by ODVA to conform
to the specification and operate in open, multivendor systems by having passed conformance
testing at one of ODVA’s authorized conformance
test service providers and having received an
official Declaration of Conformity from ODVA.
Here’s a look at the technology behind every
DeviceNet product.
Introduction
DeviceNet is a digital, multi-drop network that
connects and serves as a communication
network between industrial controllers and I/O
devices. Each device and/or controller is a node
on the network. DeviceNet is a producerconsumer network that supports multiple
communication hierarchies and message
prioritization. DeviceNet systems can be
configured to operate in a master-slave or a
distributed control architecture using peer-topeer communication. DeviceNet systems offer a
single point of connection for configuration and
control by supporting both I/O and explicit
messaging. DeviceNet also has the unique
feature of having power on the network. This
allows devices with limited power requirements
to be powered directly from the network,
reducing connection points and physical size.
DeviceNet follows the Open Systems
Interconnection (OSI) model, an ISO standard for
Network Size
Network
Length
Data Packets
Bus
Topology
Bus
Addressing
System
Features
Up to 64 nodes
Selectable end-to-end network distance
varies with speed
125 Kbps 500 m (1,640 ft)
250 Kbps 250 m (820 ft)
500 Kbps 100 m (328 ft)
0-8 bytes
Linear (trunkline/dropline); power and
signal on the same network cable
Peer-to-Peer with Multi-Cast (one-to-many);
Multi-Master and Master/Slave special case;
polled or change-of-state (exception-based)
Removal and replacement of devices from
the network under power
Table 1: Summary of DeviceNet Features and Functionality
network communications that is hierarchical in
nature. Networks that follow this model define all
necessary functions from the physical
implementation up to the protocol and
methodology to communicate control and
information data within and across networks.
The Physical Layer
DeviceNet uses a trunk-line/drop-line topology that
provides separate twisted pair busses for both
signal and power distribution. The possible
variants of this topology are shown in Figure 1.
Thick or thin cable can be used for either
trunklines or droplines. End-to-end network
length varies with data rate and cable thickness
as shown in Table 2.
©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
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Technical Overview
Figure 1: Thick or Thin Cable can be used for either trunklines or droplines
DeviceNet supports both isolated and non-isolated physical layer design of devices. An opto-isolated
design option allows externally powered devices (e.g. AC Drives starters and solenoid valves) to share
the same bus cable. The DeviceNet Specifications contain additional information concerning
component requirements, protection from mis-wiring, and examples.
DATA RATES
Thick Trunk Length
125 KBPS
500 m
(1,640 ft)
Thin Trunk Length
100 m
(328 ft)
Flat Trunk Cable
380 m
(1,250 ft)
Maximum Drop Length
6m
(20 ft)
Cumulative Drop Length 156 m
(512 ft)
250 KBPS
250 m
(820 ft)
100 m
(328 ft)
200 m
(656 ft)
6m
(20 ft)
78 m
(256 ft)
500 KBPS
100 m
(328 ft)
100 m
(328 ft)
75 m
(246 ft)
6m
(20 ft)
39 m
(128 ft)
Table 2: The end-to-end network distance varies with data rate and cable thickness.
Several different connector types can be used on DeviceNet (see Figure 2). Both sealed and unsealed
connectors are available. Large (mini-style) and small (micro-style) sizes of pluggable, sealed connectors
are available. For products that do not require sealed connectors, open-style connectors can be used.
Screw or clamp connections can be made directly to the cable if a pluggable connection is not required.
Nodes can be removed or inserted from the network without powering-down the network. A unique
feature of DeviceNet is the ability to add power taps at any point on the network. This makes redundant
power supplies possible. The trunkline current rating is 8 amps.
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©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
Technical Overview
Figure 2: Open and Sealed Connectors are available on DeviceNet
The Data Link Layer
The Data Link Layer of DeviceNet is defined by
the CAN specification and by the implementation
of CAN Controller chips. The CAN specification
defines two bus states called dominant (logic 0)
and recessive (logic 1). Any transmitter can drive
the bus to a dominant state. The bus can only be
in the recessive state when no transmitter is in
the dominant state. This fact comes into play in
the bus arbitration scheme employed by CAN.
Several frame types are defined by CAN:
• data frame
• overload frame
• remote frame
• error frame
Data is moved on DeviceNet using the data frame.
The other frames are either not used on
DeviceNet or are for exception handling. The
DeviceNet data frame format is shown in Figure 3.
CAN is a carrier sense network. Any node can
attempt to transmit a message when no other
nodes are transmitting. This feature provides
inherent peer-to-peer capability. If two or more
CAN nodes try to access the network
simultaneously, a non-destructive, bit-wise
arbitration mechanism resolves the potential
conflict with no loss of data or bandwidth. All
receivers on a CAN network synchronize to the
transition from recessive to dominant represented
by a Start of Frame bit. The identifier and the
RTR (Remote Transmission Request – not used by
DeviceNet) bit together form the Arbitration Field.
The Arbitration Field is used to facilitate media
access priority. When a device transmits, it also
monitors (receives) each bit it sends to make sure
it is the same. This allows detection of
simultaneous transmission. If a node transmitting
a recessive bit receives a dominant bit while
sending the arbitration field, it stops transmitting.
The winner of arbitration between all nodes
transmitting simultaneously is the one with the
lowest numbered 11-bit identifier. CAN also
specifies a data frame format with a 29-bit
identifier field that is not used by DeviceNet.
The Control Field contains two fixed bits and a
4-bit length field. The length may be any number
from 0 to 8 representing the number of bytes in
the Data Field. The 0–8 byte size is ideal for lowend devices with small amounts of I/O data that
must be exchanged frequently. With eight bytes,
there is enough flexibility for simple devices to
send diagnostic data, or to send a speed
reference and acceleration rate to a drive.
DeviceNet also defines a fragmentation protocol
that provides a way for nodes to transmit larger
amounts of data with minimal protocol overhead.
The CRC field is a cyclic redundancy check word
which is used by CAN controllers to detect frame
errors. It is computed from the bits that come
before it. A dominant bit in the ACK slot means
at least one receiver besides the transmitter
heard the transmission.
CAN provides very robust error checking and
fault confinement employing several types of
error detection and fault confinement methods
including CRC and automatic retries. These
methods, which are mostly transparent to the
application, prevent a faulty node from disrupting
the network.
©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
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Technical Overview
Figure 3. CAN Data Frame
The Network and Transport Layers
DeviceNet requires that a connection with a
device must first be established in order to
exchange information with that device. To
establish a connection, each DeviceNet product
will implement either an Unconnected Message
Manager (UCMM) or a Group 2 Unconnected
Port. Both perform their function by reserving
some of the available CAN identifiers. When
either the UCMM or the Group 2 Unconnected
Port is used to establish an Explicit Messaging
Connection, that connection is then used to
move information from one node to the other, or
to establish additional I/O Connections. Once
I/O connections have been established, I/O data
may be moved among devices on the network.
At this point, all the protocol of the DeviceNet
I/O message is contained within the 11-bit CAN
identifier. Everything else is data.
The 11-bit CAN identifier is used to define the
connection ID. Uniqueness of connection IDs is
strictly controlled, which is required to take full
advantage of producer-consumer capabilities.
DeviceNet divides the 11-bit CAN identifier into
four groups. The first three defined groups
contain two fields; one 6-bit field for MAC ID and
the other for Message ID. The combined fields
define the connection ID. Four messages are
used for offline communications.
Devices may be Clients or Servers or both.
Clients and Servers may be producers,
consumers or both. In a typical Client device, its
connection would produce requests and
consume responses. In a typical Server device,
its connections would consume requests and
produce responses. DeviceNet provides for
several variations on this model. Some
connections in either a Client or a Server may
only consume messages. These connections
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would be the destination for Cyclic or Change-ofState messages. Similarly, some connections in
either a Client or Server may only produce
messages. These connections would be the
source for Cyclic or Changes-of-State messages.
The use of Cyclic and Change-of-State
connections can substantially reduce bandwidth
requirements. By design, nodes in a DeviceNet
system are responsible for managing their own
identifiers. These identifiers are interleaved
(distributed) throughout the entire range. All
nodes have a full range of message priorities
available to them regardless of their Media
Access Code Identifier (MAC ID). Through the
duplicate MAC ID algorithm, the uniqueness of
CAN identifiers is guaranteed without the need
for a central tool or record for each network.
Figure 4 shows the DeviceNet allocations within
the 11-bit CAN Identifier.
A related issue is detection of duplicate nodes.
Because DeviceNet uses a device address inside
the CAN Identifier Field, it presents a mechanism
for detecting nodes with duplicate addresses.
Preventing duplicate addresses is better than
trying to locate them after they occur —
something not taken into account in other CANbased networks. Another key benefit to nodes
managing their identifiers is that a user can add
and delete nodes and/or add additional peer-topeer messages among existing nodes at any time
without having knowledge of the existing set-up.
No centralized record must be located or
reconstructed. Since nodes know which IDs are
already in use, a tool simply has to request an
I/O connection be added between the two
devices, specifying priority level, the data path
(class, instance, attribute) and the production
trigger (cyclic, poll, or change-of-state).
©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
Technical Overview
Figure 4. DeviceNet Allocations of the 11-Bit CAN identifier field
The Upper Layers: the Common
Industrial Protocol (CIP)
DeviceNet uses the Common Industrial Protocol,
called CIP, for its upper-layers. CIP is strictly
object oriented. Each object has attributes (data)
and services (commands) and behavior (reaction
to events). Two different types of objects are
defined in the CIP specification: communication
objects and application-specific objects. Vendorspecific objects can also be defined by product
makers for situations where a product requires
functionality that is not in the specification.
For a given device type, a minimum set of
common objects will be implemented. The user
benefits from interoperability among devices
regardless of the manufacturer or the device type.
Since CIP-based networks are based on a
common application layer, the application data
remains the same regardless of which network
hosts the device. The application programmer
doesn’t even need to know to which network a
device is connected. Figure 5 provides an
overview of CIP within the context of DeviceNet
and the OSI Model.
Figure 5: The CIP Object Model
©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
5
Technical Overview
CIP also defines device profiles, which identifies
the minimum set of objects, configuration
options and the I/O data formats for different
types of devices. Devices that follow one of the
standard profiles will have the same I/O data and
configuration options, will respond to all the
same commands and will have the same
behavior as other devices that follow that same
profile. A subset of the device profiles supported
by CIP and DeviceNet are shown in Table 3.
Device Profile
Device Type No.
AC Drives
02hex
0Chex
Communications Adapter
Contactor
DC Drives
DC Power Generator
General Purpose Discrete I/O
Generic Device
Human-Machine Interface
15hex
13hex
1Fhex
07hex
00hex
18hex
Limit Switch
05hex
04hex
Mass Flow Controller
1Ahex
Motor Overload
03hex
16hex
Inductive Proximity Switch
Motor Starter
Photoelectric Sensor
Pneumatic Valve(s)
06hex
1Bhex
Process Control Valve
10hex
1Dhex
Residual Gas Analyzer
1Ehex
Resolver
09hex
Position Controller
Table 3: Device Types Supported by DeviceNet and CIP
DeviceNet also has standard mechanisms for
vendors to incorporate their own features
(objects, attributes, services beyond those
defined in the device profile) into their products
in addition to the minimum required objects.
However, these additional features must be
implemented in strict accordance with the
DeviceNet specification in the manner
prescribed by the specification.
Another important feature that sets CIP-based
networks apart from other network architectures
is the ability to originate a message on one CIPbased network such as DeviceNet, and then pass
it to another CIP-based network such as
EtherNet/IP with no presentation at the
application layer. This seamless bridging and
routing capability sets DeviceNet apart from
other field bus networks. It means that a set of
objects included in the specification define the
mechanisms that a bridging device can use to
forward the contents of a message from one
network port to another without acting on the
contents of that message. When using bridging
devices that support these objects, the user’s
only responsibility is to describe the path that a
message must follow. CIP ensures that the
message is handled correctly, independent of the
networks involved.
CIP is a producer/consumer-based model, rather
than a traditional source/destination model.
Producer-Consumer networks provide for more
efficient use of networking bandwidth, A message
is produced onto the network, it is identified, not
by its destination address, but by connection ID.
Multiple nodes may then consume the data to
which this connection ID refers. The result of
this dynamic connection approach provides two
clear benefits in the efficiency of the network:
• If a node wants to receive data, it only needs
to ask for it once to consume the data each
time it is produced.
• If a second (third, fourth, etc.) node wants
the same data, all it needs to know is the
connection ID to receive the same data
simultaneously with all other nodes.
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©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
Technical Overview
The Predefined Master/Slave Connection Set
Fundamentally, DeviceNet employs a peer-to-peer
messaging model. However, it also provides for a
simplified communication scheme based on a
Master/Slave relationship. This predefined
connection scheme is known as the Predefined
Master/Slave Connection Set. This connection
method simplifies the movement of the I/O
messages most often used in control applications.
Many sensors and actuators are designed to
perform some predetermined function in which
the type and amount of data the device will
produce and/or consume is known at power-up.
Type
The Predefined Master/Slave Connection Set
provides connection objects that are almost
entirely configured at the time the device
powers-up. After powering up the network, the
only remaining step necessary to begin the flow
of data is for a “master” device to claim
ownership of this predefined connection set
within its “slave(s).” Slave devices can produce
data using one or more of the following message
types, depending on how the device is
configured and the requirements of the
application, as shown in Table 4.
Description of Operation
polled
A slave configured for polled I/O will receive “output” data from the master device
in a sequential order that is defined by the master’s scan list. The master’s polling
rate is determined by the number of nodes in the scan list, the DeviceNet baud
rate, the size of messages produced by the master and each node in its scan list
and the internal timing of the master device. For a given system configuration, this
messaging method will provide deterministic behavior. Polled I/O “output” data can
be unicast or multicast.
cyclic
A device configured to produce a cyclic I/O message will produce its data at a
precisely defined interval. This type of I/O messaging allows the user to configure
the system to produce data at a rate appropriate for the application. Depending on
the application this can reduce the amount of traffic on the wire and more
efficiently use the available bandwidth.
change-of-state
A device configured to produce change-of-state (COS) message will produce data
whenever it changes, or at a base heartbeat rate. This adjustable heartbeat rate
provides a way for the consuming device to know that the producer is still alive
and active. DeviceNet also defines a user-configurable Production Inhibit Time that
limits how often COS messages are produced to prevent nodes from “flooding” the
bandwidth. Users can adjust these parameters to provide optimum bandwidth
utilization in a given application scenario.
Table 4: Slave I/O Message Types in the Predefined Master/Slave Connection Set
©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
7
Technical Overview
Conformance Testing
ODVA Conformance Testing is designed to
validate that a product complies with relevant
aspects of the ODVA specification, from the
physical layer through the application layer.
Devices that have passed ODVA DeviceNet
conformance testing have passed all of the
following tests at one of ODVA’s authorized test
service providers:
Control and Information Protocol (CIP) test
verifies that a product meets requirements of
CIP and the additional messaging and
services required for DeviceNet. It tests
conformance at the device profile,
application layers.
DeviceNet Electronic Data Sheet (EDS) test
verifies that the product’s EDS (an ASCII text
file supplied by the manufacturer) contains
the correct grammar and all the required
product information, including the device’s
identity, supported message types,
configuration parameters and parameter
enumeration. This file is used by network
configuration software tools to help set up
devices on the network.
DeviceNet Physical Layer test verifies that a
DeviceNet product’s physical layer is
designed and operating correctly. For
example, it confirms that voltage and current
levels remain in allowed ranges during
operation and that the connectors and
indicators meet ODVA specifications.
DeviceNet™ System test verifies that the
product operates in a multi-vendor DeviceNet™
system. The product is installed in a 64-node,
multi-vendor environment and run in a variety
of situations specifically designed to identify
potential interoperability and system problems.
Products must successfully establish explicit
and I/O connections during various power-up
sequences, and they must survive the on-line
removal and replacement of other nodes. The
test also confirms that the device will operate
under heavy network traffic with scanners
from multiple manufacturers and that the EDS
file can be used to configure the device.
ODVA also offers specialized testing:
DeviceNet Power Supply test verifies that
network power supplies provide the
necessary voltage and currents, and operate
as the specification requires, under a variety
of loading conditions.
Semiconductor test is another level of testing
for DeviceNet products used on
semiconductor manufacturing tools. Products
submitted for semiconductor-specific tests
must first pass the standard test suite. This
additional level of testing verifies
conformance of connectors, indicators,
switches, isolation, power, and object
behavior with the ODVA specification
supplement Interface Guidelines for
DeviceNet Devices on Semiconductor
Manufacturing Tools, including compliance
with CE and SEMI S2.
Once a product passes the appropriate conformance tests, ODVA grants the vendor the right to use its
conformance marks. A list <www.odva.org/10_2/04_products/04_prodtest.htm> of conformance-passed
products also appears on the ODVA web site. Users who wish to specify only products that have passed
conformance tests can find them listed online or identify them by these product marks.
www.odva.org
[email protected]
DeviceNet™ and CIP™ are trademarks of ODVA. DeviceNet CONFORMANCE TESTED® is a registered certification mark of
ODVA. EtherNet/IP™ is a trademark used under license by ODVA. ControlNet™ is a trademark of ControlNet International.
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©copyright 2004, Open DeviceNet™ Vendor Association, Inc., (ODVA)
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