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the architecture for distributed automation
Since the Modbus protocol was
introduced in 1979, it has been adopted
in manufacturing applications through-
out the world. At this time over 7.2
million Modbus nodes exist in North
America and Europe alone. Over the
last year, Modbus-IDA has worked
with standards organizations across the
globe to further the goal of openess
and accessibility of Modbus – the most
popular industrial protocol in the
Recognition in China
Modbus is used extensively in Chinese
manufacturing operations. In October
2004, the Standardization Administra-
tion of China (SAC) formally launched
three standards for industrial automa-
tion in the People’s Republic of China:
• GB/Z 19582.1-2004 Modbus
Industrial Automation Network
Specification Part 1 – Modbus Applica-
tion Protocol,
• GB/Z 19582.2-2004 Modbus
Industrial Automation Network
Specification Part 2 – Modbus Protocol
Implementation Guide over Serial Link,
• GB/Z 19582.3-2004 Modbus
Industrial Automation Network
Specification Part 3 – Modbus Protocol
Implementation Guide over TCP/IP.
This move heralds even greater prolif-
eration of Modbus in the Pacific rim,
especially with the opening of a local
protocol conformance test laboratory,
currently under development.
IEC Acceptance
Adoption of Modbus TCP in China
followed close upon the heels of the
IEC acceptance of Modbus as a
Publicly Available Specification, putting
Modbus TCP on the pre-standard
Hannover Fair 2005 • Special Issue
The specification defines mapping
services so that CANopen devices can
communicate over a Modbus TCP
network via a gateway device or
through the incorporation of a local
Modbus TCP transport layer. Access
to the entries of a CANopen object
dictionary is supported on both a read
and write basis, along with a variety of
device control functions.
For users, this specification increases the
options for communicating via
Modbus TCP by standardizing the way
Modbus communications will be used
with CANopen. This also decreases the
opportunity for multiple incompatible
approaches proliferating.
IAONA Commitment
Last year at
Hannover Fair
was pleased to
participate in the
signing of a Memorandum of Under-
standing (MoU) with IAONA, the
purpose of which is to help avoid a
multitude of “different and partially
proprietary solutions.” IAONA and its
partners seek to bring harmony and
standardization where possible to serve
both users and suppliers.
In keeping with its commitment to
openness and accessibility, Modbus-
IDA continues to build relationships
that support open standards. Parallel,
incompatible paths serve to complicate
rather than simplify the work of the
industrial control and automation
community. Modbus-IDA is pleased to
report significant progress in the last
year moving toward greater openess to
benefit all constituencies.
Modbus on the Move
Modbus TCP and a companion
protocol known as RTPS were submit-
ted to IEC SC65C as a
real-time industrial
Ethernet suite. The
Modbus-IDA organization
was granted a type D
liaison status by the IEC, at which time
the specification was accepted as a New
Work Item by the subcommittee.
Modbus TCP/IP was the first PAS to
be approved during the submittal
period in September 2004.
At present the organization is working
on reformatting the specification, which
was requested by several national
committees. This will allow it to be
better integrated into the revision of
IEC-61158 (Ed 4.0 2007), the well-
known fieldbus standard.
Modbus Mapping by CiA
In March 2005, Modbus-IDA and
CAN in Automation (CiA) announced
an agreement, resulting in Specification
CiA DSP 309-2: Interfacing CANopen
with TCP/IP Part 2: Modbus/TCP
Mapping. CiA DSP 309-2 provides a
standardized mapping of CANopen
data for transport on Modbus TCP
networks. In the specification, Modbus
Function Code 43/13 is reserved for
this purpose.
CiA will maintain the
specification, which will
be available for CiA
members on the CiA
( and for
Modbus-IDA members upon request
News about the World’s Most Popular Industrial Protocol
Standards Activities • Standards Activities
Modbus-IDA Technical Committee News
Conformance Test Policy
mittee is currently reviewing the
Modbus TCP test specification, which
will be the basis for revising the test
software package. This work will also
become the foundation for a new
specification for testing conformance to
the protocol for Modbus over serial
The group is using the current specifi-
cation, developed by the Sensor Bus
Laboratory at the the University of
Michigan as the starting point for this
A policy that includes a strictly moni-
tored self-test option for Modbus-IDA
members is also under review. Modbus-
IDA will continue to offer nonmember
companies and companies that prefer to
outsource their device testing an
outside laboratory option.
The new policy will include guidelines
for in-house testing, outside laboratory
work, re-testing requirements, and test
result publication. The program will
From the Modbus User’s
and Modbus Developer’s
Join one of
technical groups:
IT Infrastructure
Conformance Test
Device Description
Safety Layer
Real Time
Modbus Protocol...
Jeff wrote to the Forum:
Modbus is supposed to be an open
protocol, but why can’t I get the entire
list of commands that I can issue? For
example, I’d like the ability to stop the
PLC and issue the write program to
flash command from our MMI. Is
there a way to get this information?
Bud Buyer responded:
Modbus ASCII, RTU and TCP are
open protocols. The instruction set
includes read and write instructions.
It’s up to the device manufacturer to
supply the the specifics of the imple-
mentation of the registers, addressing
and the associated word format used in
any given device.
It is unlikely that you are missing
instructions, but you might be missing
certain registers that will do what you
want to accomplish. Or maybe your
device doesn’t offer Modbus access to
control features that you need.
In any event, you need to direct your
inquiry to the device manufacturer for
Curt Wuollet added:
That is, no doubt, a proprietary exten-
sion to the protocol as it would be
specific (hopefully) to a particular
vendor. I would suggest a serial proto-
col analyzer.
Max Power’s comment:
I use the manufacturer’s reserved
commands with my own proprietary
data within the Modbus packet. The
command numbers are listed in the
spec but there are reserved commands
for other uses and future uses. Some of
these uses could be for network routing
and relaying and other special devices
expand options for testing and make it
easier for members and non-members
to certify the conformance of their
devices to the Modbus protocol.
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 2005 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 communica-
tion protocol suite and the evolution to address architectures for distrib-
uted 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 implementa-
tion by users resulting in reduced costs.
Standards Activities • Standards Activities
Q&A continued...
besides special programming and other
commands for Modicon equipment.
From Lynn A. Linse:
The info you want is VERY product
specific, thus to do this you’ll need to
first query the device and confirm
which product and firmware rev it is.
Then generate a large list of devices that
behave as you expect. This is one
reason you WON’T find this info in the
public space - it is too complex to
describe and support. Each new gen of
PLC adds “new” functions, so these
commands are a moving target.
You may be better off with a DOS
utility from SE (if there is one) that you
can run in an OS child shell to reflash a
SE uses function 0x7E as a “catch all”
for things like this (at least on newer
equipment). The form is just SA 0x7E
LN SF ???, where SA is slave address,
LN is byte count of remaining com-
mand, SF is some function code (such
as start or stop PLC), and ??? is up to
249 bytes of data per the function.
The start/stop PLC would be easy to
reverse engineer. The reflash of the
program will be harder and you’ll need
to work this out repeatedly for differ-
ent PLC generations.
Is there some kind of guideline where
I could read how to create a Modbus
TCP server? How do I have to define
the registers?
I already checked out the
messaging on TCP/IP Implementation
from Modbus-IDA, but there
was nothing said about this task.
Curt Wuollet replied:
The registers are virtual. They can be
pointed at hard memory addresses, an
array abstraction, hardware, anything
addressable. Why couldn’t you simply
use an array or two? Even the least
flexible visual tools must support
some sort of array. Probably not the
best for efficiency, but with hundreds
of megabytes of RAM the point is
Fred Daniali suggested:
Creating a Modbus TCP server is
simple... you must know the address
registers of the information that you
wish to poll from the controller. I
recommend that you contact quark
They could help you out with things.
Lynn A. Linse added:
See my white paper on creating multi-
vendor Modbus/TCP servers (slaves)
The register design is up to you - but
be aware that many MB/TCP clients
do NOT like ranges with holes (i.e.:
4x00100 & 4x00110 both exist, but
reading 11 registers starting at 4x00100
causes error because 4x00109 does
NOT exist). Write-Only registers are
another no-no since some DCS
demand to write-then-readback the
value to confirm correct behavior.
And so on - my paper covers such
Key thing to avoid: just reading the
Modbus/TCP spec won’t create a
100% troublefree device. You need to
take into account ASSUMPTIONS
existing products will make about
your device.
Curt Wuollet replied:
I would add that it’s a fine thing you
are doing sharing your real world
experience. It will save countless hours
and aggrevation dealing with the non-
standard standard. Just think of the
enormous amounts of time wasted
across the automation realm with
everyone discovering the same prob-
lems and reinventing the wheel
because they labor in isolation. If ever
there was a need for a cooperating
community it’s here. This list is a small
step. If we could get people working
on an open platform where informa-
tion is a given rather than a product
we would advance far more quickly.
It’s crippling working with closed
Building Modbus TCP
Gibbi wrote to the Developer’s Forum:
I am new to Modbus TCP. I did a lot
of tests and think I understand the
messages, which I have to send be-
tween client and server. But, the main
problem I am working around is to
understand how the Modbus server
defines its registers. I am trying to
implement this server with labview - a
tool where I can’t influence memory
allocation, memory addresses and so
Committees Work
on Modbus’ Future
Ken Crater
for more information
or to join a
committee or
technical group.
Modbus Products and Innovations
Bluetooth Web Enabler by
Using a standard Web browser, the BLUETOOTH WEB ENABLER™ allows
users to control and exchange information, storing it as Web pages on the
device’s internal Web server. Web pages can be customized with standard HTML
tools or a text editor, and the user interface can be modified to control every-
thing from industrial devices to parking meters. The Bluetooth Web Enabler
provides several options to access your device: locally using Bluetooth, remotely
using Ethernet/Internet, and globally using GSM/GPRS.
Adds a Web user interface to your device, which is controlled using a
regular Web browser.
Gives flexible access through Bluetooth or an Ethernet interface.
Communicates using standard products (PC/PDA/mobile phone).
Allows you to change the user interface on the embedded Web server
without affecting the client.
Supports RS232/422/485 communication as well as several industrial
fieldbus protocols such as Modbus.
Offers wireless Internet access using the BWE as a Bluetooth access point.
Can be used as a data logger for local data acquisition.
For more information about the BLUETOOTH WEB ENABLER™ visit
connectBlue’s website,
BLUETOOTH is a trademark owned by the Bluetooth SIG Inc.
Phoenix Contact’s I/O
Modules with Modbus/TCP
Phoenix Contact’s new Inline Block I/O modules for Modbus/TCP
enable simple and fast integration of I/O modules in Ethernet
systems. Connection is established by mounting the modules onto a
DIN rail, connecting the power supply and network cable, and
assigning an IP address.
Equipped with 16 fixed inputs and 16 assignable inputs/outputs, and
with all the flexibility of a modular I/O system, the modules are
adaptable for use in many applications. The function of each I/O
channel is assigned by connecting an actuator or sensor. The modules
do not have software and/or parameters that need to be set. Web-
based management for simple configuration, SNMP services, and
the possibility of getting firmware updates on site round off the
product range.
One new feature of the Ethernet-capable I/O modules is the
integrated three-port switch. This makes it possible to attach more
Ethernet appliances to the devices using the second RJ45 socket, thereby saving costs and leaving ports on
the structural elements free. Installation is made more flexible and it is possible to set up a linear topology.
The modules are well suited for use in particularly small terminal boxes thanks to their flat design and a
height of just 55 mm.
With the bus coupler for the Inline Modular System, the FL IL 24 BK, the Modbus/TCP user can take
complete advantage of Inline functionality. The seamless connectivity of the Inline system reduces adaptation
time between the systems to a minimum.
Modbus Products and Innovations
Eaton’s Modbus Network
Adapter Certified
Eaton Electrical, Inc.
( With a direct
focus on speed, productivity, diagnos-
tics and system
design, the D77D-
EMA Ethernet
Modbus Network
Adapter provides
superior integration
of IT, motor
control and D77 IO products. Three
powerful features are combined into
one module: Modbus TCP, RS-485
serial Modbus, and a Modbus Pass-
Through from Modbus TCP to serial
The device also features Quick Con-
nect Port (QCPort) connectivity.
The D77D-EMA was certified through
Modbus-IDA’s device conformance test
program, to test policy version 2.0.
Control Solutions’
 10/100
Based in White Bear Lake, Minnesota,
Control Solutions, Inc.
( offers the
Buster 10/100,
fully configurable
to Modbus/TCP
gateway. The Modbus master is used to
make Modbus/TCP devices accessible
on a LonWorks network. The Modbus
slave is used to make LonWorks
devices accessible on a Modbus/TCP
The Babel Buster 10/100 gateway is
also available in a wireless version using
IEEE 802.11b.
A Modbus master, Babel Buster 10/
100 can poll a single Modbus slave IP
address, and can be bound to any
number of LonWorks devices. A
Modbus slave Babel Buster 10/100
responds to a single IP address, and
may be bound to
any number of
LonWorks devices.
LonWorks network
variable data is
translated to Modbus register data, and
vice versa. Modbus polling rates and
LonWorks network update rates are
fully configurable. Register mapping
and network variable types (SNVT) are
also fully configurable.
isoLynx Data Acquisition System
Ethernet Modbus Network
Adapter D77D-EMA
Dataforth Announces
the isoLynx
Dataforth Corporation
( introduced its
new isoLynx SLX100 data acquisition
system. An intelligent, high-speed, fully
isolated distributed system, the isoLynx
offers maximum flexibility for analog
and digital I/O selection.
The system is comprised of a 12-
channel base system including an I/O
controller module and optional 8- or
16-channel expansion backplanes, all of
which can be panel or DIN rail
mounted. The system accepts single-
channel digital or analog I/O modules,
and all I/O is channel-to-channel
isolated. The company’s SCM5B signal
conditioning module family is used for
analog I/O, and its SCMD miniature
digital modules provide digital I/O.
One I/O controller module can
operate up to 60 channels of differen-
tial analog I/O and 128 channels of
digital I/O.
The I/O controller module contains a
powerful high-speed microcontroller,
A/D and D/A subsystem, communi-
cation interface, system memory and
status LEDs. The system is modular in
design and all wiring remains connected
to the system when accessing I/O
modules, making field service and
upgrades easy.
The isoLynx SLX100 can interface to a
broad spectrum of analog signals,
including millivolt, volt, milliamp, amp,
thermocouple, RTD, potentiometer,
slidewire, strain gage, AC to true RMS
output, frequency, two-wire transmitter,
and transducers requiring DC excita-
The user can mix
and match any
I/O module type on a per-channel
basis to reduce wasted I/O channels
and save costs.
The isoLynx SLX100 communicates on
RS-232/485 serial links up to 115.2
kbps or 10Base-T Ethernet with TCP/
IP protocol and, in the near future,
fieldbus protocols such as Profibus,
DeviceNet, Modbus, and others. Up
to 16 systems can be multi-dropped on
the RS-485 serial link. Optional
fieldbus protocol communication
boards are factory installed, but are
field replaceable or upgradeable
without processor re-configuration.
BabelBuster 10/100
List your company’s
Modbus compatible
products on the
Modbus-IDA website.
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