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Modbus Organization Newsletter, December 2011
WCT Makes Modbus
Mapping Progress
The Modbus Subcommittee of the Wireless Coop-
eration Team (WCT) continues to work on the pro-
ject and has made strides in conceptualizing the
gateway parameters. Committee members have
made some initial decisions to design a gateway
specification that will be as straightforward and
simple as possible.
Look for regular updates on the gateway specifica-
tion development over the coming year.
Blog Focuses on Security
Modbus Organization member company Byres
Security (a Belden company) last week reported
on a hacker who showed how he could easily
hack into a SCADA system controlling the wa-
ter utility in the City of South Houston.
this blog entry,
Eric Byres discusses the vul-
nerability of passwords and the inherent risk
password protection poses to critical systems.
With tips for choosing "memorable yet effec-
tive" passwords, there's good advice here for
Welcome to New Members!
Advanced Micro Controls Inc (AMCI)
Bentek Systems Ltd.
Define Instruments
Domat Control System s.r.o.
Trebing & Himstedt Prozeßautomation
Modbus Device
Directory Expanding
The Modbus Organization has maintained a
directory of Modbus products — hardware de-
vices and software programs — since launch-
ing its current website in 2008. Today there are
almost 1200 listings, affording users the ability
to search for products for their projects based
on a variety of criteria.
Recent entries include an increase in the num-
ber of wireless devices, well as the number of
devices and programs focusing on energy man-
The directory lists Modbus Conformance-tested
devices first, followed by member companies'
products. Non-member listings are also in-
cluded, but do not include either spec. sheets or
Contact us
to inquire about adding your com-
pany's Modbus products to the directory or how
to find the right Modbus device for your appli-
Wishing you all peace
and good fortune
in the new year!
News about the World’s Most Popular Protocol
Member News
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Trebing + Himstedt
is an
international supplier of products
and services for the optimal use
of IT in the production
environment. The company
supports customers in their
manufacturing processes,
allowing targeted access to
Member News
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Bentek Systems,
based in
Calgary, Canada, is a company
dedicated to the design and
manufacture of industrial
Advanced Micro Controls Inc
is a U.S.-based
manufacturer with a global
presence. Its industrial controls
are sold all over the world,
including eight different product
families: Stepper Motor Controls,
PLC Modules, Rotary Sensors,
Networked Devices, Standalone
Solutions, Packaging Systems
Controls, and Stamping Press
Founded in 1985, AMCI leverages
an international network of
distributors, so customers can
quickly and conveniently
purchase products, no matter
where in the world they are
In May, AMCI announced
Modbus TCP support for the
company’s robust NR25 series
production and process
information through continuous
integration across different
communication levels – from the
automation level to the ERP
In its Industrial Communication
business unit, Trebing +
Himstedt's products ensure the
availability of industrial
networks. The Manufacturing
Integration business unit
encompasses solutions for
production IT, particularly for
Manufacturing Execution
Systems in SAP environments.
wireless SCADA and telemetry
solutions. The company provides
products and services to
industries including oil and gas,
water and wastewater, mining
and manufacturing.
SCADALink is Bentek Systems'
own line of SCADA & automation
products. The SCADALink line
includes integrated RTU/
Radiomodems, cellular- and
Internet-enabled RTU/
Radiomodems, wireless Ethernet
radios, serial Ethernet gateways,
wireless I/O telemetry, solar-
powered RTU systems, alarm
callout systems, and protocol
Modbus Newsletter
This is the newsletter of the
Modbus Organization, the
international nonprofit
organization devoted to the
evolution and support of the
Modbus protocols.
For more information about
membership and other services,
please refer to our website:
Newsletter Editor:
Lenore Tracey
Copyright 2011
Modbus Organization, Inc.
The Modbus Organization Mission
The Modbus Organization, Inc. is a group of
independent users and suppliers of automation
devices that seeks to drive the adoption of the
Modbus communication protocol suite and the
evolution to address architectures for distributed
automation systems across multiple market
segments. Modbus Organization also provides the
infrastructure to obtain and share information about
the protocols, their application, and certification to
simplify implementation by users resulting in
reduced costs.
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Reliability: High and Costs: Low
For a wastewater treatment
plant, reliability is of great im-
portance. The removal of waste-
water and stormwater in extreme
situations must happen when
required. Costs are also impor-
tant, and the key is to ensure
cost-effectiveness without com-
promising the reliability and sus-
tainability of the wastewater
treatment plant.
At Bjerringbro Wastewater
Treatment Plant in Denmark,
data registered by Dedicated
Controls is effectively transmit-
ted wirelessly via a CIM 250
communication interface module.
This has reduced the need for
manual inspection, improved pre-
ventive maintenance and en-
sured reliability of the wastewa-
ter facility.
Bjerringbro is located in mid-
Jutland, Denmark. The Bjerring-
bro Wastewater Treatment Plant
is one of 22 wastewater treat-
ment plants serving 250 pumping
stations operated by Energi Vi-
borg. Bjerringbro Wastewater
Treatment Plant has 35 pumping
stations, four of which run
Grundfos pumps transmitting
data wirelessly via CIM 250.
The Situation
Prior to the installation of the
wireless solution at the pumping
stations connected to the Bjer-
ringbro Wastewater Treatment
Plant, manual inspections were
necessary on a weekly basis for
local pumping stations and daily
for main pumping stations, to
ensure correct operation and to
detect possible faults. This re-
quired that staff be present at
the treatment plant every day of
the week, all year round.
Previously, the warning sys-
tem at one of the local pump-
ing stations consisted of
lamp placed high up on a
lamppost; and reaction to a
warning depended on the
lamp being seen and reported!
Today, wireless transmission
sends the full register of
pump pit activity every ten
minutes to the SCADA system
at Bjerringbro Wastewater
Treatment Plant.
The Grundfos solution
Using the terrain cabinet at
the Engvej Øst local pumping
station as an example, the
robust cabinet includes a me-
Sewage pump controller with a CIM 250 mod-
ter and a sewage pump con-
ule and GSM/GPRS modem are to the right.
troller (Dedicated Controls)
with a CIM 250 module that
has a GSM/ GPRS modem with
Winpager software – a log pro-
its own IP address and mobile
gram for SCADA on the com-
phone number. The use of a SIM
puter at the treatment plant –
card to establish the wireless
sets the schedule, ensuring the
connection makes installation
alarm is sent to the correct per-
easy, as the GSM/GPRS operator
sonnel at the right time, accord-
delivers the communication in-
ing to five pre-determined levels
of alarm situations and response
“Wireless transmission
means we get data here and
now – and that’s data we
can use,”
says Kaj Lorenzen,
Driftsleder, Bjerringbro Ren-
The data transmitted includes
the main status of the pump pit
and pumps and users can re-
quest active alarms and warn-
The types of alarms include sew-
age overflow, low flow, dry run-
ning, under-voltage, blocked mo-
tor/pump, over-temperature, and
others that can be adapted ac-
cording to the user's needs.
Currently, there are about 200
of these cabinets installed in
Denmark with Dedicated Con-
trols transmitting wirelessly via
the CIM 250 module.
Data is communicated wirelessly
every 10 minutes to the central
SCADA system. In an alarm
situation, the SCADA system
ensures correct alarm handling.
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Wireless Water...
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Comtrol Announces
Modbus Router
Comtrol Corporation
nounced Modbus Router, the lat-
est firmware application for its
DeviceMaster UP Industrial
Gateway family of products. The
Modbus Router firmware was
developed to provide network-
wide Modbus connectivity be-
tween a wide variety of Modbus
masters and local and remote
Modbus slaves. Modbus Router
provides a highly flexible and
easy-to-use connectivity solution.
What can Modbus Router do?
Simultaneously connect up to
123 Modbus masters to as
many as 255 Modbus slave
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cont’d from pg 3
The Outcome
The immediate benefits of the
wireless communication offered
by the CIM 250 arise from the
system showing how a pumping
station is running over an entire
day. This helps save time and
money by reducing the need for
manual inspections and helping
make better planning possible.
In time, this means greater reli-
ability from better preventive
Two-port version of
Anybus CompactCom
HMS Network's
two-port ver-
sion of Anybus CompactCom for
Modbus TCP is a fast and easy
way for industrial device manu-
facturers to achieve connectivity
to Modbus TCP. It also reduces
the need for expensive external
switches and cuts down on fac-
tory wiring since the module
comes with a built-in switch of
its own.
The new two-port Modbus TCP
module includes an integrated
switch that makes it possible to
build networks in normal field-
bus style (daisy chain) rather
than connecting all devices
through an external switch. This
reduces the need for expensive
external switches.
Personnel only get called out if
absolutely necessary and they
can act earlier. In addition, the
wireless system provides opera-
tional data for control and statis-
tics. This increases the possibil-
ity of even greater measures for
ensuring maintenance planning,
operational reliability, and also
for optimising efficiency in the
future, because all data is saved
in a database.
Automatically detect local
slave devices and route mes-
Connect serial Modbus mas-
ters to Modbus TCP net-
works and remote Modbus
slave devices
Convert Modbus protocols,
such as Modbus/TCP to Mod-
Deliver diagnostics and
status pages to enhance
maintenance and problem-
solving capabilities
Solve common problems such
as relocating devices or con-
necting additional Modbus
masters to an existing instal-
Comtrol’s Modbus Solu-
tions web page
for more info.
Advertise on the
Modbus.org Website
a half million pages served to
almost 30,000 unique visitors each
what better place to advertise
your Modbus devices and software ?
Contact us
for a rate sheet. A special
member's discount makes banner
advertising an even better deal when
you join the Modbus Organization.
Anybus CompactCom
ule acts as a slave on the Modbus
TCP network. It is available with
and without housing and is about
the size of a compact flash card.
The core of the module is com-
posed of HMS's NP30 microproc-
essor with its integrated fast
Ethernet controller along with
RAM and Flash memory for the
Modbus TCP device software
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Modbus Discussion
Modbus Discussion
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Modbus Discussion
Q&A from the Modbus Discussion Forum...
Modbus writing 16-bit signed (-) values
neilrudds asked:
Hi, I'm new to the forum and
quite new to the Modbus protocol
and I'm hoping someone can help
me with my Modbus problem.
I am using RS485 to communi-
cate with a generator engine con-
troller. The controller stores a
series of event records across sev-
eral string type registers that
contain firstly date, time and
event log reason; secondly the
state of all inputs/outputs of the
engine (this works well and is not
the issue).
The issue is:
To acquire this data I must first
write to a 16-bit signed register
the actual ID of the event record
before I can read out the data.
The record ID's range from 0 to
approx. -1200 depending on the
records logged.
I have had success writing from 0
to -128 and the correct records
are then contained in the appro-
priate registers, but after -128, I
have many problems. For exam-
ple, when trying to write -384, I
am actually given record -128 but
-385 is ok and gives me the cor-
rect record. And again writing -
256 give me -256 but -257 gives
me -1. I have looked at the binary
values etc. and cannot see a prob-
Any help is greatly appreciated!
Rob replied :
It sounds like something some-
where is getting 8-bit and 16-bit
words confused.
8-bit signed numbers range from
-127 to +128
16-bit signed numbers range
from -32766 to +32767
If you are familiar with the "2s
Compliment" notation you will
understand how negative num-
bers are encoded - i.e. if the MSB
is SET then the number is nega-
tive. http://en.wikipedia.org/wiki/
In your case it appears that when
you write a value where bit 8 is
set (i.e. the MSB of an 8-bit word)
it will appear as a negative inte-
ger value. I suspect from your
symptoms that you are either
writing 8-bit words or your device
is expecting 8 bits instead of 16.
Lynn Linse suggested:
This isn't really a Modbus prob-
lem as Modbus literally moves all
registers as 'unsigned 16-bit'.
Modbus is the delivery truck &
doesn't care what's in the pack-
The problem is in how your code
is packing your signed integer
into that unsigned 16-bit word.
Your signed INT is likely 32-bit if
a PC or modern embedded sys-
tem, but perhaps 8-bit if your
system is trying to highly mini-
mize data memory usage.
Since a PC is also little-byte first
and Modbus is big-byte first, this
makes packing a signed integer
from 'host form' to 'Modbus form'
I can't explain how you accom-
plish this, but since the most
common design is something
modbus[0] = (X >> 8) AND 0xFF
modbus[1] = (X AND 0xFF)
Your symptom sounds like your
first equation is always resulting
in 0xFF. The shift-right (>>) op-
eration may have unexpected
consequences on a signed inte-
ger in some systems.
Read more or add your com-
to this thread.
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