ModbusNews_Oct2009.pdf

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Newsletter

October 2009

Modbus Members at

ISA EXPO 2009

Several Modbus Organization member companies are

exhibiting next week at the ISA EXPO 2009 Show in

Houston, Texas. Need a device that “speaks” Modbus or

advice on a Modbus issue? Experts at these firms are

available to help.

A list of these companies and the booths where they can

be found follows:

•

Hirschmann

1509

•

Kepware Technologies

1325

•

MatrikonOPC

1335

•

MOXA

2501

•

Phoenix Contact

1231

•

ProSoft Technology

2127

•

Sealevel Systems

2437

Member Companies

Offer Modbus

Learning Tools

Whether you’re a noobie or an old hand, you may be

interested in checking out some of the Modbus tutorials

made freely available by our member companies.

For a nice review of Modbus

implementation, go to

Control Solution’s

Modbus

101

tutorial:

www.csimn.com/CSI_pages/Modbus101.html

The tutorial covers topics such as:

• What is Modbus?

• Where do I start?

• Review of Modbus Register Types

• Review of Modbus Function Codes

• Modbus: When 40001 really means 1,

or 0 really means 1

• If registers are 16-bits, how do I read Floating

Point or 32-bit data?

• How many devices can I have on a Modbus network?

Acromag

also offers an extensive

Introduction to Modbus TCP/IP

its website (registration required):

www.acromag.com/supi_tutorials.cfm.

For a discussion specific to Modbus RTU,

Real Time

Automation

provides a tutorial,

Modbus RTU Unplugged

– An introduction to Modbus RTU

Addressing, Function Codes, and Modbus

RTU Networking

at:

www.rtaautomation.com/modbusrtu/

This paper includes topics such as

• Modbus RTU Drawbacks

–

Reporting by Exception

• Data Object Properties

• Modbus RTU versus Other Protocols

• Difference Between Modbus RTU and Modbus TCP

continued on page 6

modbus-tk: a python

implementation of Modbus

A new project has been listed on the Modbus

Organization

’

s Technical Resource page

(www.modbus.org/tech.php). Modbus Test Kit (modbus-

tk ) is an implementation of the Modbus protocol in

Python that supports Modbus RTU and TCP for writing

masters and slaves. The developer

’s

main purpose in

making this tool available is to make the development of

testing tools as easy as possible. (The Python language is

flexible and easy to learn and to use.) Modbus Test Kit is

distributed under GNU LGPL license. Note that

modbus-tk is different from pymodbus, which is an

implementation of the Modbus stack in python.

The Modbus.org site offers links to third-party sites for

Modbus users

’

and developers

’

convenience. These are

not under the control of the Modbus Organization, and

we are not responsible for the contents of any linked site

or any changes or updates to such sites. The inclusion of

these links does not imply endorsement of the site by the

Modbus Organization or imply approval of any content,

recommendation or application.

News about the World’s Most Popular Industrial Protocol

Member News • MemberNews

Meet Some of Our Members...

Proportion-Air, Inc.

is a manufacturer

of electronic air pressure regulators

and air flow control valves. Founded in

1985, Proportion-Air offers a large

family of electronic air pressure

regulators and air flow control valves

Located in central

Florida,

Motor

Protection

Electronics

was

founded in 1983,

and offers a full line

of industrial

controls for the

water and wastewater industry.

MPE’s Station Controller series

(SC1000 & SC2000) are SCADA-ready

pump controllers designed to perform

level control in a wide range of lift

station applications. The SC1000

operates the pumps based on selected

setup values and the wet well level

signal.

The source of the level input signal is

menu selectable as either a 4-20 mA

transducer or a 10-point conductance

probe. The SC1000 alternates the

pumps, performs lag pump delays,

provides high and low alarms, and has

a variety of control options available in

the setup menu to customize the

controller to the application.

(www.mpelectronics.com)

SCADAmetrics’

mission is

straightforward: to offer innovative,

industrial-grade SCADA Gateways for

water meters.

The company’s patent-pending

EtherMeter was developed to erase the

communication barrier between

Encoder Registers and PLCs, RTUs,

and SCADA controllers. The

EtherMeter Gateway is equipped with

two meter interface ports and three

PLC/RTU/SCADA interface ports. It

operates by reading Encoder Registers

using the appropriate AMR protocol

and transmitting the corresponding

totalization and flow data to the

SCADA equipment using industrial

protocols, such as Modbus, DF1,

EtherNet/IP™, raw ASCII, and

ADAM-4000.

SCADAmetrics’ EtherMeter Interfaces

are targeted toward the SCADA,

industrial control, and commercial

submetering arenas. The EtherMeter is

optimized for control system

applications, and contains a plethora of

features for applications in these

markets.

(www.scadametrics.com)

PROPORTION

www.proportionair.com

THE FUTURE OF CONTROL

™

that allow you to select the best

product to match your exact

application requirements.

The company recently released a

Modbus version of its electro-

pneumatic pressure control and flow

control valves equipped with Modbus.

Modbus serial communications

capability is available on the popular

QBT, QPV, and QB3 series of

pressure control valves, which operate

as Modbus slaves.

(www.proportionair.com)

Shouldn’t your company

be a member?

Modbus Newsletter

This is the newsletter of the Modbus

Organization, the international non-

profit organization devoted to the

evolution and support of the Modbus

protocols. For more information about

membership and other services, please

refer to our website: www.modbus.org

Newsletter Editor:

Lenore Tracey (lenore@modbus.org)

Organization, Inc.

PO Box 628

Hopkinton, MA 01748 USA

ph +1-508-435-7170

fax +1-508-435-7172

info@modbus.org

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 communica-

tion 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.

Modbus Discussion

Q&A

Modbus master control...

Luís Soares asked the forum:

I want to know how I can solve the

following situation:

I have one system that communicates

using Modbus protocol and RS485

bus, with some network analyzers. I

would like to put another Master on

the line to make some requests to the

network analyzers too.

The problem is that probably with two

Masters on the line the messages will

get screwed [up] and there will be

collisions for sure.

Is there any hardware device (to which

I can connect both Masters) that I can

use to connect both systems to be able

to manage the requests on the line? This

device would buffer the requests from

the two Masters and avoid problems

on the line.

Or is there another way to solve this

problem?

Jerry Miille replied:

The MARC Multii-Port

(www.miille.com/din366-10p.pdf) is

commonly used for connecting

multiple Modbus Masters to a network

of one or more Modbus Slaves. It

works as you describe by buffering the

messages and only replying to the

Master that made the request. You can

contact me directly if you have any

questions. Jmiille [at] miille.com

From the Modbus Discussion Forum…

criders had some thoughts and

some questions:

I think that you would have to find a

way to sync the two Masters somehow.

When one of the Masters is

communicating, then the other one

doesn’t, What type of Masters are you

using, PLCs or PCs? Also are you using

ASCII or RTU?

If you are using the RTU framing

protocol, you could extend the silent

interval of one of the Masters. Instead

of a silent interval of 3.5 characters, try

setting one Master’s silent interval to

something like five characters. This

might give you enough of a window

to perform the communications.

I never had to use two Masters before,

so if you try it, please use caution.

Patrick L commented:

HMS makes a gateway that is a

Modbus RTU Slave to Modbus RTU

Slave. Connect one Master to one of

the Slaves and the other Master to the

other Slave. The gateway has a fixed

mapping of 512 Bytes In and 512

Bytes Out.

For more info, go to ww.anybus.com

or send me an email at: support [at]

hms.se

Lorne had another suggestion:

Check out the PLC09 Arbitrator

(www.calta.com). It was developed for

exactly this application.

Add your commects to this thread

at modbus.control.com/thread/

1253888117

Find the best way to engage...

email sales@control.com to:

•

plan the optimum strategy for

social media engagement

•

develop a program to meet

your goals and budgets

Modbus-IDA Discussion Forums

Modbus Discussion

MBLogic Free Soft Logic -

Release...

In February, Michael Griffin

announced:

The MBLogic Free/Open Source

software project has a new release. The

package, which has been known as

MBServer, now has soft logic

incorporated into it, and as a result is

now known as MBLogic. This has

been the goal of the project from the

beginning.

This is Free Software released under a

GPL license. You can use it free of

charge, modify it, re-distribute it, etc.

The user-visible parts of the software

have been designed to make it fairly

simple to strip out the “MBLogic”

branding, so if anyone wants to

redistribute this under another brand

name, that should be pretty straight

forward.

MBLogic has the following features:

Q&A

From the Modbus Discussion Forum…

standard MS-Windows newline (CR-

LF) characters in the text files (for easy

editing). The “tar.gz” package will

probably also work on OS/X, but I

don’t have a Mac to test it on, so I can’t

say for sure.

Installation instructions are in a PDF file

located in each package.

The project web site has not been

updated yet (coming soon), but the

packages are online, as well as new

screen shots.

The web-based HMI has been tested

with the following web browsers:

Firefox (Linux and MS-Windows).

Opera (Linux and MS-Windows).

Epiphany (Linux). Google Chrome

(MS-Windows). Apple Safari (MS-

Windows). The HMI does *not* work

with MS Internet Explorer, as that

browser is based on outdated

technologies and does not have the

features needed for a graphical display.

The help and status web pages

however *do* work in MS IE (tested

with version 8). The help and status

web pages, of course, work with all

the other browsers as well.

The new soft logic feature is based on

the MBLogicEngineCk libraries, which

were previously released as a stand

alone library. The instruction set and

addressing are fully documented in the

online help. At present, programming is

IL only (ladder support is in the

planning stages).

The system ships with a demo

program that will run on start up. The

soft logic program now controls the

HMI “tank” demo screen that was

used in the previous MBServer release.

If you modify the sample soft logic

program, the changes will be reflected

in the HMI behavior. The soft logic

and HMI can be changed while the

system is running via the status web

management interface (effectively,

“online programming”).

I would appreciate it if people would

download this and give me feedback.

Recently, Rudi asked:

Can the MBLogic software be adapted

to work with I2C (I²C) and X10? I

would use it to replace the software I

use today in my home automation

system.

If not, could you please point me to

some cheap Modbus I/O systems? I

need about 64 digital outputs and 16

analog inputs.

Michael Griffin responded:

I haven’t implemented any drivers for

I2C or X10, as I don’t have any suitable

hardware to test with. For inexpensive

Modbus TCP hardware, I would

suggest looking at Advantech. I’m

assuming you want the I/O as

distributed blocks, in which case the

ADAM 6000 series is probably the

most suitable.

From Rudi:

I was thinking maybe I can use a

Modbus to I2C converter. Googling

for such a thing I got the idea to maybe

program a micro-controller to do this.

There are some with I2C already on

board. Don’t know if somebody

already did.

Read the rest of this thread and add

your suggestions at

modbus.control.com/thread/

1235372036

Modbus users & suppliers

get together on the

Modbus Community for:

•

Interactivity

•

Knowledge aggregation

•

Contact with Modbus

users and suppliers

Discussion supported by...

Modbus TCP client and server.

•

Web-based graphical HMI.

•

Online (web-based) help (more than

40,000 words). This has been

completely revised since the

previous (MBServer) release.

•

Online (web-based) status

monitoring. This has been

completely revised since the

previous (MBServer) release.

I am looking for people to use it and

would appreciate feedback.

The MBLogic_2009-02-22 package is

available at:

http://sourceforge.net/projects/

mblogic/

There are two versions of this

package. The “tar.gz” package is for

Linux, and the “zip” package is for

MS Windows. Both are identical,

except the MS Windows version has

had the files modified to use the non-

•

Soft logic (PLC) programmability

•

Networking to field I/O through

Modbus Discussion

More from the Modbus Discussion Forum…

Kepware Modbus TCP with Serial Server...

In September, Jay Banks wrote:

I have an issue and I’m sure someone

has run into this before.

Setup:

• B&B ESP901 serial server

• Kepware OPC

• hmisys.com Modbus slave sim

• Modbus TestPro

I set up an old IBM laptop with a

Modbus slave simulator configured on

it. Seems to work fine.

Using Kepware OPC, I set up two

different devices: one TCP and one

serial, with the serial using a virtual

comm port.

On Kepware, the TCP poll fails, but

the serial (on the virtual comm) works

fine. The B&B was configured for

multiple connections, so that isn’t the

issue.

Using a program called Modbus

TestPro, I can poll the laptop using

TCP and it also works. BUT, I can only

poll it when I select “raw” TCP.

I’m thinking that since it works on my

secondary program, Kepware may be

using normal TCP and the B&B only

works with raw TCP packets.

I can’t find anything on changing these

settings on Kepware or the B&B.

If anyone has run into this, I would be

interested in hearing solutions.

Ryan Plester responded:

With Modbus, there are in general two

ways to communicate via TCP/IP. The

first (which Kepware seems to be

using) is Modbus TCP. This is basically

the regular Modbus serial protocol

with some header information sent via

TCP/IP.

The second method is usually referred

to as Modbus RTU via TCP. This is

exactly the same as the Modbus serial

protocol except that it is sent via TCP/

IP. This protocol does not have the

additional header information that

Modbus TCP has. This sounds like the

“raw” mode of your other

applications.

I am not certain how to set this up in

Kepware’s OPC sever but the

MatrikonOPC server for SCADA

Modbus has this as a selectable option

for each Modbus device you connect

to. Also, the OPC server for Modbus

allows you to specify this by using the

terminal server configuration option.

Contact MatrikonOPC Support at

support@MatrikonOPC.com or 780-

945-4011.

Mark (PeakHMI) offered this:

I tested the Modbus TestPro with the

PeakHMI Modbus TCP simulator and

one other simulator. I could only run

Modbus TestPro in demo mode and

the results are the same for both

simulator programs.

Both programs received the same

request and both responded with the

same data and then Modbus TestPro

gives an error “Could not send

outgoing packet.” I assume that is

because it is not registered.

From the help dialog in Modbus

TestPro “raw” means without the TCP

wrapper. I do know the PeakHMI

simulator and the other one I tested

with will not respond to a “raw”

message.

Everest Software also has a Modbus

Master/Slave OPC server (serial and

TCP). You might want to give it a try.

Jay replied:

I will say that Modbus TestPro will

work just fine unregistered. The only

thing it will do is annoy the heck out of

you with a pop-up. Which means you

must have something set up wrong.

I’m no expert on test software, but

Modbus TestPro is very reasonably

priced and one of the best programs I

have used. Or at least I can say, it is

much better than any free Modbus

master I have tried, and much cheaper

than most other commercial software I

tried.

The Modbus serial slave sim, on the

other hand, works, but is a little quirky

at times. But hey, it’s free!

Bill Graham (Industrial Thinking)

commented:

I am not familiar with the B&B

terminal server but the packets used

for TCP Modbus and serial Modbus

are different.

You can either use a device like a

Lantronix box with Modbus firmware

(UDS1100 may have been superceeded

now) to do the packet adjustment for

you or you can set up a serial Modbus

device in Kepware and tick the use

Ethernet Encapsulation option. This

effectively sends the Modbus packets in

serial format over raw TCP.

Jay answered:

The Ethernet Encapsulation option

worked. I did mess with that yesterday,

but I now see I wasn’t doing it right.

Am I right in thinking that “virtual”

comm ports aren’t the best way to do

things. It seems that in a large setup, you

wouldn’t want to load a large number

of virtual drivers on a system.

Kepware’s Fred Loveless chimed in:

If you set the B&B converter to be a

Modbus TCP to Modbus Serial

converter then you can use the Modbus

TCP driver to talk to the serial devices

and the converter will strip the Modbus

TCP Header and footer from the

message and send a normal serial

packet.

If the converter is just configured as a

Serial to Ethernet converter, then you

would use the Modbus Serial driver

and select Etherent Encapsulation. This

sends a raw Modbus serial packet over

Ethernet. Essentially this is what the

virtual comm port is doing as well.

E-mail technical support at Kepware

and they can help trouble shoot it

more.

Add your commects to this thread

at modbus.control.com/thread/

1253728575

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