DVA
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1999, ODVA - Open Vendor Association, Inc.
Open Vendor Association, Inc.
DeviceNet Technical Overview
What is the DeviceNet?
DeviceNet is a low-cost communications link to
connect industrial devices (such as limit switches,
photoelectric sensors, valve manifolds, motor
starters, process sensors, bar code readers,
variable frequency drives, panel displays and
operator interfaces) to a network and
eliminate
expensive hardwiring.
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.
DeviceNet is a simple, networking solution
that reduces the cost and time to wire and
install industrial automation devices, while
providing interchangeability of “like”
components from multiple vendors.
DeviceNet is an
open network standard
. The
specification and protocol are open — vendors
are not required to purchase hardware, software
or licensing rights to connect devices to a system.
Anyone may obtain the DeviceNet Specification
from the Open DeviceNet Vendor Association,
Inc. (ODVA) for a nominal reproduction charge
(currently $250 USD + postage). Any company
that manufactures (or intends to manufacture)
DeviceNet products may join ODVA and
participate in technical working groups that are
developing enhancements to the DeviceNet
Specification.
Buyers of the DeviceNet Specification receive an
unlimited, royalty-free license to develop
DeviceNet products. Companies looking for
assistance may purchase sample code that eases
their implementation, development toolkits, and
development services from many sources. The
key hardware components are available from the
largest worldwide suppliers of semiconductors.
Why the DeviceNet Communication Link?
For years the process industry has been
attempting to develop a single, open standard to
address all kinds of field devices. The original
scope of their standards effort was aimed at
replacing the 4-20 mA standard with a single
digital standard. As the scope increased to
address complex and sophisticated services (such
as high data rate communications between
controllers, time synchronization of large
numbers of devices scanning at very high speeds),
the development of a single standard became
delayed.
At the same time, the cost of communication
technology has dropped considerably in recent
years, making it cost-effective to connect simple
devices never considered for SP50 fieldbus
directly to a network. Such a standard for simple
devices requires the same level of interchange-
ability as exists for 120/220 VAC and 24 VDC
discrete, hardwired I/O. DeviceNet allows the
interchangeability of simple devices while making
interconnectivity of more complex devices
possible. In addition to reading the state of
discrete devices, DeviceNet provides the
capability to report temperatures, to read the load
current in a motor starter, to change the
deceleration rate of drives, or to count the
number of packages that have passed on a
conveyor in the previous hour.
Controller Area Network (CAN) is the key to
low cost products.
The DeviceNet communication link is based on a
broadcast-oriented, communications protocol –
the Controller Area Network (CAN). The CAN
protocol was originally developed by BOSCH for
the European automotive market for replacing
expensive, wire harnesses with low-cost network
cable on automobiles. As a result, the CAN
protocol has fast response and high reliability for
applications as demanding as control of anti-lock
brakes and air-bags. Chips are available in a
variety of packages with high temperature ratings
and high noise immunity, attributes well suited for
the industrial automation market as well.
DeviceNet™ Technical Overview
Page VI