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the architecture for distributed automation
ISA 2004 Exhibition • Special Issue
intends to make this reformatting a
priority for the organization.
Jean-Jacques Poubeau, VP of Major
Programs at Schneider Electric and a
Modbus-IDA board member, also
commented: “Modbus, the only
industrial messaging protocol already
recognized by the Internet world (port
502) has one of the largest installed
bases worldwide with more than 7.2
million installed nodes. With this
positive vote, the Modbus TCP-IP
profile has been accepted by the IEC
as a Publicly Available Specification and
is now eligible to become part of
future editions of the International
Standards IEC 61158 and IEC 61784-
2. This is a significant step forward for
the efficient, proven and cost effective
Industrial Ethernet solution supported
by Schneider Electric.”
Modbus TCP Accepted as IEC
Publicly Available Specification
Modbus TCP put on “Pre-Standard” track
The ubiquitous Modbus protocol,
whose ownership was recently trans-
ferred from Schneider Automation to
an independent nonprofit organization,
Modbus-IDA, has been accepted by
the IEC as a Publicly Available Specifi-
cation (PAS).
The TCP variant of the protocol, along
with a companion protocol known as
RTPS, were submitted to IEC SC65C
as a real-time industrial Ethernet suite.
The submission was made possible by
the recent granting of a type D liaison
status to Modbus-IDA by the IEC.
Of 25 countries voting on the pro-
posal, there was only one negative vote,
reflecting overwhelming approval of
the specification. At the same time, the
specification was accepted as a New
Work Item by the subcommittee.
Modbus-IDA President Ken Crater
stated, “We are delighted to be the first
PAS to be approved during this
submittal period. Although our
organization is quite new, this approval
reflects the outstanding acceptance that
Modbus has received in the industrial
marketplace over the past 25 years.
More significantly, however, this
Publicly Available Specification repre-
sents our organization’s dedication to
bringing a new level of openness to
industrial communications.”
In approving the document, several
national committees asked for a
reformatting of the specification to
allow for better integration into the
revision of IEC-61158 (Ed 4.0 2007),
the well-known fieldbus standard.
According to Crater, Modbus-IDA
Schneider Automation Transfers Modbus Copyright to Modbus-IDA
We were delighted to announce the
recent transfer of the Modbus protocol
on April 12, 2004. In a dramatic move
signaling its dedication to the openness
of the Modbus protocol, Schneider
Electric transferred its copyright in the
protocol to Modbus-IDA. The agree-
ment, which was signed by Schneider
Automation, Inc., and Ken Crater,
president of Modbus-IDA, transferred
the protocol, including the entire “right,
title and interest” in the protocol
copyright. This was publicly announced
at the Hanover Fair trade show in
According to Crater, “This transfer
establishes a milestone in the inevitable
migration of our industry toward open
protocols. It’s only fitting that the most
widely implemented protocol on the
industrial landscape is now in the hands
of a nonprofit organization committed
to its further proliferation and evolu-
tion.” Crater announced the
organization’s intent to pursue interna-
tional standardization for the protocol
in the near future.
Jean-Jacques Poubeau, VP of Schneider
Electric stated that “By transferring the
Modbus protocol rights to Modbus-
IDA, a nonprofit and independent
organization, Schneider Electric dem-
onstrates its willingness to move
toward really open systems and archi-
tectures based on open standards and
vendor-independent protocols. The
association of Modbus protocol with a
standard Ethernet TCP-IP stack makes
available the first really open and
vendor-independent Industrial Ethernet
News about the World’s Most Popular Industrial Protocol
Standards Activities • Standards Activities
All the World’s Standards Groups Agree
Well, it may not be as momentous as
that, but five of the world’s Ethernet-
related standards groups, including
Modbus-IDA, signed a Memorandum
Of Understanding with IAONA at the
2004 Hanover Fair. The MOU pro-
vides the basis for the organizations to
work together under the IAONA
framework toward common solutions
to some of the remaining issues in the
design and management of industrial
Ethernet networks.
Key to the MOU is the fact
that there are still a number of
“white spaces” – that is, areas
in which the various standards
groups have not yet developed
divergent technologies – and it
is in these white spaces that the
organizations have agreed to
work toward agreement to
avoid further divergence of
practice. Some of the areas
anticipated by the MOU
include system issues such as
name space management,
security issues, cabling and the
use of IEEE 1588.
Organizations signing the MOU, in
addition to Modbus-IDA and IAONA,
include Interest Group SERCOS
Interface (IGS), Open DeviceNet
Vendors Association (ODVA), Ethernet
Powerlink Specification Group (EPSG)
and Ether-CAT Technology Group
(ETG). The agreement provides each
organization with a seat on the IAONA
Technical Steering Committee, and the
ability to participate in all IAONA Joint
Technical Working Groups.
RFC Process
Approved by
Modbus-IDA Board
In a move bringing the same standard
of openness enjoyed by the public
Internet to the world of industrial
standards, the Modbus-IDA board
recently approved an “RFC” (Request
For Comments) process for the
organization’s standards efforts.
The essence of the RFC process is to
encourage broad-based contribution
of new ideas into the standards-making
process, followed by periods of open
public comment and discussion.
Rather than the closed-door process
perceived by many to dominate in our
industry, this means that any change or
extension to Modbus standards will
take place in full public view with
opportunities for all points of view to
be heard.
The Modbus-IDA RFC is implemented
on the organization’s website, where
new initiatives may be submitted for
discussion. Also available on the
website is a flowchart document
illustrating the path taken by RFC
Guiding the RFC process will be a
series of technical committees now
being formed by the organization (see
related story at right). These commit-
tees will work with RFC authors to
coordinate submissions of similar
intent, improve clarity of submissions,
assist in the integration of comments
and make recommendations for final
RFC approvals.
The technical committees will also be
able to initiate RFCs, to insure that
significant areas of technology are not
neglected in the Modbus-IDA evolu-
tionary process.
For more information on the RFC
process, refer to
and follow the link to “Modbus
Community - Developers Corner.”
The initial framework is now in place,
to be more fully populated as the
technical committees commence their
The Modbus-IDA Newsletter
This is the newsletter of Modbus-IDA, the international nonprofit organization
devoted to the evolution and support of the Modbus and IDA protocols.
For more information about membership and other services of Modbus-
IDA, please refer to our website:
Newsletter Editor: Lenore Tracey
Copyright 2004 by the Modbus Organization, Inc.
PO Box 628, Hopkinton, MA 01748 USA
ph +1-508-435-7170 • fax +1-508-435-6929
The Modbus-IDA Mission
Modbus-IDA is a group of independent users and suppliers of automa-
tion devices that seeks to drive the adoption of the Modbus communi-
cation protocol suite and the evolution to address architectures for
distributed automation systems across multiple market segments.
Modbus-IDA will also provide the infrastructure to obtain and share
information about the protocols, their application and certification to
simplify implementation by users resulting in reduced costs.
Standards Activities • Standards Activities
Modbus-IDA Forming New Technical Committees This Year
Modbus-IDA is proud to announce the
initiation of its technical evolution
work, with the formation of five new
technical committees and a marketing
committee. This evolution will prima-
rily take place through the Request For
Comments process (see article at left).
These groups, composed of Modbus-
IDA members and invited guests, will
be primarily responsible for developing
and/or guiding extensions, modifica-
tions and supplements to the Modbus
specification as they progress through
the RFC process.
Most of the work will be accom-
plished via email, and most meetings
held via conference call, making it easy
for busy people to participate.
ments of certain application categories.
The effort may include the coexistence
6. Marketing.
Not a technical group, this committee is
engaged in the study of Modbus-IDA
marketing activities on behalf of its
members’ interests. Discussion to date
has focused on trade show activity, but
other initiatives such as regional work-
shops, publications and etc. will also be
Any member interested in participating in any
of these committees is encouraged to contact
Ken Crater at to get
more information or to sign up!
Members are being
welcomed now to help
with Modbus technical
of Modbus TCP with conventional IP
traffic. Again, some of this effort
(notably IEEE 1588 implementation
and Ethernet frame prioritization) will
involve a liaison function with IAONA.
1. IT Infrastructure.
This group will work on system-level
issues, such as security, adoption or
adaptation of additional IP protocols,
application services, and network
installation, performance and manage-
ment. There will also be a liaison
function with relevant IAONA Work-
ing Groups.
From the Modbus User Forum…
Store and Forward...
“I am told that this is not part of the
Modbus RTU protocol standard. Can
anyone with more expertise with
Modbus RTU protocol confirm this?”
Max Power replied: “The minimum
time to begin a response 3.5ct, but
there is no maximum. It could be 1
minute, 10 minutes, etc.”
Meir Saggie added: “A store & for-
ward mechanism is not part of
Modbus specs. (in particular, one that is
heard by the Master).
“In Modbus, the Master expects
precisely one reply to its query – good
or bad. In the latter case, the transaction
simply failed. It is up to the “user” of
Modbus to retry or not. (exception – a
Broadcast query does not expect any
“In other words, the Master in your
case does not have the slightest idea of
where the ‘reply’ came from (the store
& forward machine in your case) – it
simply assumes it is from the slave and
processes it as such.
“As a practical solution, you may want
to insert a delay, so your Master is
‘deaf ’ for the amount of time the store
& forward machine ‘talks’.”
2. Conformance Test
Already an active group, it’s purpose is
to further define and develop our
conformance testing program and
guide the efforts of our conformance
test lab(s). This includes the definition
of conformance classes and test
3. Device Description.
The focus of this group is to work on
the structure and mechanisms to
associate semantics with devices. This
work may evolve to include many of
the former IDA Group issues, includ-
ing object definitions and distributed
4. Safety Layer.
This group is concerned with the
definition of a safety layer and related
5. Real-Time.
This group will work on one or more
real-time solutions to meet the require-
On May 18, a user wrote: “In our
SCADA system the master transmits a
request message and then listens for a
proper reply message from a slave for
a timeout period of 1 second.
“With a store and forward implemen-
tation on a common radio frequency,
the master, after transmitting a request
message to the store & forward slave,
will ‘hear’ the store & forward station
request message and reply before it (the
master) receives a proper reply message
from the store & forward station.
“The Modbus RTU driver I am using
expects to receive a proper reply
message immediately after it transmits a
request message. If it hears anything
other than a good reply it sets a
timeout error code even though a
good reply is eventually received within
the timeout window.
“If the master receives a message or
messages that are NOT a proper reply
before it receives a message that IS a
proper reply, shouldn’t the Modbus
driver just ignore the improper mes-
sages and accept the proper reply
message if it is received before the
Ask your question or help out another user on the Modbus Community Forums: for users or for developers.
Promoting Modbus • Promoting Modbus
Modbus-IDA at
We’re looking forward to our next
successful trade show appearance at
ISA/2004, the enormously popular
U.S. venue for the controls and instru-
mentation industries. As in our previ-
ous booths, we’re putting our members
and their products on prominent
display, as the most compelling way of
demonstrating the overwhelming
popularity of Modbus in the industrial
It Was Huge, and a Huge Success!
Modbus-IDA at Hanover Fair 2004
Making its first public appearance as
“Modbus-IDA,” our organization set
up shop for the week at the enormous
and impressive Hanover Fair. Our
efforts were met with great success,
and we carried our organization’s
message to many new companies in the
world automation market.
Five sponsoring members joined
Modbus-IDA in our debut appearance.
Our well-staffed booth featured the
products and literature of sponsoring
companies ACTL, HMS, Jetter,
Niobrara, and Schneider Electric,
whose representatives were joined by
Modbus-IDA President Ken Crater
and Executive Director Lenore Tracey.
Modbus expert Dr. Rudy Belliardi of
Schneider Automation was also on
hand to answer even the most difficult
technical questions posed by visitors to
our booth.
Two major events highlighted the week
for our organization. First was the
announcement of the transfer of the
Modbus copyright from Schneider
Automation to Modbus-IDA, a
milestone of monumental importance
to the move toward open protocols.
The second event was a signing cer-
emony at the IAONA booth. Repre-
sentatives of five major protocol
organizations signed a Memorandum
Of Understanding pledging coopera-
tion to avoid further divergence of
protocols in areas where standards do
not currently exist.
For the sponsoring companies, the
major event was the flow of current,
new and potential customers into our
booth and the forming of relationships
that will spell continued success for
years to come. We were happy to
make new friends with our booth
companions, and also happy to hear
that most of our booth partners will
join us in Houston for ISA/2004.
For Modbus-IDA, one of the greatest
values in our Fair appearance was the
opportunity to have in-depth discus-
sions with our member companies. We
come back from the Fair with new
ideas, new energy, and enthusiastic
commitments from numerous mem-
bers to participate in our technical and
marketing groups. We look forward to
working with you in the months and
years ahead to keep Modbus-IDA the
open and responsive organization it
was designed to be, and to keep the
Modbus protocol open and responsive
to the changes in our world.
This year’s booth at ISA will feature
displays by the following booth
• Control Technology Corporation
• Harting
• HMS Industrial Networks
• Niobrara R&D
• Schneider Automation
Each booth partner will have a free-
standing kiosk with an overhead sign
and banner emblazoned with their
company’s identification. We intro-
duced a new Visibility Package with the
ISA/2004 appearance, and Precision
Digital and Scadaware are participating
at this level.
Join the Modbus-IDA
Marketing Committee
and help us help you!
Participate by email!
Modbus Products and Innovations
Acromag I/O Module Gains
Modbus Certification
Acromag, Incorporated
(www., a Michigan-based
designer of analog and digital control
products for the industrial I/O market,
recently had its
BusWorks 900EN
Ethernet I/O Module
certified. The
product family consists of a variety of
analog and
discrete input/
output modules
for monitoring
sensors and
devices. Each
remote I/O
module provides
a 10/100
Modbus TCP/IP interface and up to
12 channels in an inch-wide unit. Major
features include 10/100 auto-negotia-
tion; configuration from a standard
web browser; and up to 12 channels
per stand-alone module. Analog inputs
accept TC, mV, RTD, VDC, and mA
signals; analog outputs provide VDC
or mA signals. Discrete I/O has 0-35V
DC range. An advanced/ruggedized
5-port Ethernet switch accessory is also
available in a compact 1-inch Din Rail
package. BusWorks 900EN Ethernet
I/O Modules have CE approval, UL,
cUL, and CL1 Div 2 Groups ABCD
approvals are pending. The product
comes with a five-year standard
& UDP protocols and require no
proprietary cabling or network hard-
ware. Modbus function support
includes function codes 1, 2, 3, 4, 5, 6,
15 and 16.
When used in intelligent devices that
have their own micro-controller, the
AnyBus-IC is connected to the device’s
processor using a serial 2-wire TTL
interface. The AnyBus-IC is responsible
for the entire protocol handling so that
the microprocessor in the field device is
not tasked unnecessarily with bus
For use with simple processor-less
devices such as valve terminals and
modular I/Os, the AnyBus-IC has a
clocked shift register interface, which
can be directly connected to up to 128
input signals and 128 output signals.
The AnyBus-IC automatically detects
how much I/O data is connected to
the shift register during the Power On
phase. This makes it easy to implement
variable I/O configurations such as
those typically used in modular I/O
In addition to the Modbus-TCP
application protocol, the AnyBus IC
also has a wide range of embedded
Internet functions: embedded web
server with access to dynamic device
data and the possibility to embed Java
applets and scripts; on chip file system
with 1.4-Mb user memory for data and
programs; Telnet access, FTP file
transfer and functions for sending e-
The AnyBus-IC for Ethernet is an
addition to the AnyBus-IC device
The 4201-MNET-MCM and 5201-
MNET-MCM gateways support RTU
and ASCII modes of Modbus, and can
be configured with up to 100 com-
mands per port, making it a very
powerful device interface and data
For more information on the 4201-
email prosoft@prosoft- or visit www.prosoft-
New Modbus Gateway
from ProSoft Technology
ProSoft Technology
has announced
its new ProLinx Modbus to Modbus
TCP/IP Gateways, the
MCM and 5201-MNET-MCM.
gateways provide interface communi-
cation for Modbus-compatible devices
to Modbus TCP/IP The Ethernet
communication port provides a high-
speed client and server connection.
Data is exchanged between the proto-
col drivers over an internal data file.
The Modbus TCP/IP client driver
supports the active reading and writing
of data with Modbus TCP/IP com-
patible devices. The devices support
standard TCP/IP support using TCP
HMS Industrial Networks
Introduces Modbus-TCP
on Chip
A new single chip-controller for
Modbus-TCP and embedded Internet
is available.
HMS’ AnyBus-IC
combines a powerful 32-bit micro-
controller with flash and RAM
memory, a 10/100 Mb Ethernet
controller and all the analogue functions
of an industrial-grade fast Ethernet
interface on a footprint of only 9 cm
The small size and reduced interface
costs now make it possible to imple-
ment an Ethernet interface for simple
field devices.
...the listings of Modbus
compatible products at
The chip is packaged in a 32-pin dual-
in-line case and requires only a 5 Volt/
250mA power supply. The Ethernet
interface provides 100 Mbps full
duplex data transmission, and the
integrated 32-bit microprocessor
guarantees short protocol processing
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