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Modbus RTU over Ethernet
I have a situation where I have to transmit Modbus RTU over Ethernet. Does anyone know of a device that will accept the Modbus RTU data via ethernet (10-base-T) and send it out RS485...

I have a situation where I have to transmit Modbus RTU over Ethernet. We have the link working now using a client on the NT network.
The Modbus slave is configured at the NT server and uses the comport on a client to transmit and recieve request for the data. We have another device which converts the RS232 from the client comport to RS485 which is what the Modbus master accepts. Does anyone know of a device that will accept the Modbus RTU data via ethernet (10-base-T) and send it out RS485.
Thanks for any suggestions

Try looking at Modicons Wedge.

By Cameron Haegle on 13 September, 2002 - 4:03 pm

Look at the Digi One IA RealPort product. It has support for just what you are looking for and much, much more. Their site is "http://www.digiia.com":http://www.digiia.com . This device supports RS-232, RS-422 and RS-485, using either a standard DB-9 or 9-pin screw terminal box.

It looks pretty slick too. ;)

I think GE make something called a VersaMax Se which is a Ethernet to serial bridge which will work for Modbus. Here is a link to the brochure.

"http://www.geindustrial.com/products/brochures/GFA-226.pdf":http://www.geindustrial.com/products/brochures/GFA-226.pdf

Also I have tested a unit called a TigerLINK with is a Serial server. It makes a virual com port on your computer and links it to an IP address that the TigerLINK is then connected to. It has two serial ports. Each one can be configured for RS232 or RS485. You can find more info at "http://www.atoptechnologies.com":http://www.atoptechnologies.com .

Also Horner APG (hornerocs.com 317-916-4274) makes small inexpensive PLC's with integrated operator interface call OCS's. Modbus TCP/IP slave is an option on them. Also, they each have serial ports that can be configured to be Modbus Masters or Slaves from ladder.

Eric Moore
eric.moore@heapg.com

By Trevor Marson on 10 September, 2002 - 2:49 pm

North Communications can collect values from MODBUS, and pass them over TCP/IP, in HTML if necessary - visit "www.northcomms.com":http://www.northcomms.com

By Danny Jameson on 10 September, 2002 - 12:29 pm

You may wish to research SIXNET. They off an Ethernet to serial converter that supports modbus protocol. See "www.sixnetio.com":http://www.sixnetio.com .

Look at the Mediator "www.envenergy.com":http://www.envenergy.com

By Robert Willis on 10 September, 2002 - 1:26 pm

The Schneider Electric 174CEV30010 Modbus Ethernet Bridge has a 10MB 10BASET port and a RS232/485 Serial port.

You can download information on the device from "www.modicon.com":http://www.modicon.com

Regards
Robert Willis
Square D Company
Houston, Texas
E-Mail: willisr@squared.com

> I have a situation where I have to transmit Modbus RTU over Ethernet. We have the link working now using a client on the NT network.
> The Modbus slave is configured at the NT server and uses the comport on a client to transmit and recieve request for the data. We have another device which converts the RS232 from the client comport to RS485 which is what the Modbus master accepts. Does anyone know of a device that will accept the Modbus RTU data via ethernet (10-base-T) and send it out RS485.
> Thanks for any suggestions

I have seen very nice componnents for gateway solution called 'Anybus Comunicator' incl. Modbus RTU to Modbus TCP.

Look at "www.hms-networks.com":http://www.hms-networks.com

Regards.

By Edgar Dohmann on 10 September, 2002 - 4:28 pm

The PC132 module by Ortech Engineering Inc. has two Ethernet ports and 2 serial ports. Both Ethernet ports support 10BASE-T or 10BASE-FL for TCP/IP or MODBUS/TCP communication. Either serial port can be configured for RS232 or RS485 communication. MODBUS/RTU is supported on either serial port. MODBUS/TCP is also available on the serial ports using PPP. For more information see our web site at http://www.ortech-engr.com or contact me directly.

> I have a situation where I have to transmit Modbus RTU over Ethernet.<

This is going to be a problem, because Modbus RTU has rather tight timing requirements. This means that any "virtual serial cable" solution you use may or may not work, depending on how closely the existing devices insist on the standard timing. You may be lucky, or not.

The "proper" way of doing it would be to convert the data to something like Modbus/TCP for transmission over the Ethernet. However, it seems a bit of an overkill. OTOH, it would provide a clear upgrade path out of the mess by allowing either end to be repaced by a native Modbus/TCP
product some way down the track, independently of the other end.

Jiri
--
Jiri Baum <jiri@baum.com.au> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools

Look at "http://www.sixnetio.com/htmlhelps/catalog/5a8c983.htm":http://www.sixnetio.com/htmlhelps/catalog/5a8c983.htm or
"http://www.digi.com/solutions/devtermsrv/devsrv/digioneIA.shtml":http://www.digi.com/solutions/devtermsrv/devsrv/digioneIA.shtml or others that have been mentioned from time to time in this list.

By Richard Theron - FieldServer on 12 September, 2002 - 1:30 pm

Hi

FieldServer Technologies "www.fieldserver.com":http://www.fieldserver.com has a Modbus serial to Ethernet protocol converter. The serial port can be configured for RS-232 or RS-485. If is very easy to set up the serial port as a master or salve, serial speeds from 300 to 115K bps.

Regards,
Richard

By Lynn August Linse on 12 September, 2002 - 3:12 pm

There are many devices today which can do this - my company ( "www.digi.com":http://www.digi.com ) sells many. You can also do a search of the web for "terminal server" or "device server".

The biggest issue you may have is a is that your average TS or DS won't understand the need to send a full Modbus/RTU message on the RS-485 without pause or gap. In other words, many general TS or DS products treat the network and serial receive as critical, but treat serial transmission as low-priority. These may fail to keep sending the serial data with few msec gaps. So it helps to have a product which officially understands this is Modbus and insures the serial transmission is not interrupted.

One other unique feature of special Modbus-enhanced TS or DS - since they understand Modbus protocol message framing, they can allow many
Modbus/RTU-in-TCP or Modbus/TCP masters (clients) to share a single RS-485 multi-drop. In other words, your design (so far) is a single WinNT Master polling your RS-485. With a fully Modbus-aware product, you could actually have more than one Master concurrently connect "via ethernet (10-base-T) and send it out RS485".


Best Regards::

Lynn August Linse, alist (at) linse.org
IA Firmware Specialist, Digi Int'l (www.digi.com)
26741 Portola Pkwy, Suite 1E #242
Foothill Ranch CA 92610-1743 USA
Ph/Fx: 949-916-1524 (auto-detect voice or fax)

Go to google and type "Modbus RTU over Ethernet", exactly as your subject line reads. This might lead you to other searches like "RS232 to RS485 Converter", "What is Modbus/TCP". You will
get several good hits on these topic. Then come back to control.com and ask a more specific question, like "which of the products that I have
read about really work ?" "Are there others ?"

My opinion only.

Jay Kirsch

Jay,
That's just it...we have tryed a couple devices that companies say will do this. But it turns out they can't.
Thanks

Yup, there are some products out there that claim to be able to tunnel industrial protocols over Ethernet. This is not an adequate specification. I think you want to pick a product
that explicitly states in its specification that it can tunnel *Modbus RTU* protocol over Ethernet and that the maker has tested and deployed it in that purpose.

I understand your problem and you did do some footwork on this.

Modbus RTU has tight timing constraints that serial protocols, in general, do not. Did you try the Lantronix CoBox ? This product has a complete spec. ( I decided not even try this myself, for the reason below. )

I would suggest not using serial tunnelling gadgets at all, and use an MEB instead. Serial tunnelling devices do not really place a legacy Modbus slave on a network. Instead, they just
replace the serial wires with a CAT5 cable, making a point to point connection.

An MEB will put the Modbus RTU slave on an Ethernet network. With an MEB, the slave will be able to respond to concurrent requests for information from multiple masters. For about
the same amount of money you can get an MEB. See the offerings from Modicon, Control Microsystems, and Niobrara on this. These dogs will hunt.

There are some much more detailed explanations on control.com, written primarily by Lynn August Linse, on this topic. You can hunt through the archives here to find these posts for a more complete answer.

Jay Kirsch

By Cameron Haegle on 13 September, 2002 - 10:12 am

Look at the Digi One IA RealPort "http://www.digiia.com":http://www.digiia.com . It supports multiple industrial Ethernet and serial protocols, including ModbusTCP and Modbus RTU/ASCII. It also has a multi-electrical serial support that can operates in RS-232, RS-422 and RS-485 modes.

Cameron

I made a software to do that. It's a bridge between modbus RTU (serial port) and Modbus/TCP/IP
It's running under any version of Windows.

Modbus TCP communications are about to get a lot cheaper... Take a look at "www.ipsil.com":http://www.ipsil.com and their Sensor Block and Alarm Block. They could implement Modbus TCP in their Serial Block.

Check out the $1 web server article.


Dennis