Modbus RTU over Ethernet

hi,
Does anyone know how to do modbus rtu over ethernet?
I need to send a message from PLC (over ethernet)to a devices that used RS 485 interface without protocol conversion. So it just need a gateway to setting the interface such as 9600 baud 8N1 and setting the IP of the ethernet and then I can send/receive the messages. Is there a gateway can do this? Please give me the link

Thanks

digi one iap can do protocol conversions like this.

Which protocol (Modbus TCP or Modbus RTU) and which physical interface (Ethernet or RS485) does the PLC have ?

What model of PLC are you using ?

The usual method to do this is for the PLC to use Modbus/TCP and for the gateway device to convert Modbus/TCP to Modbus RTU on RS-232 or RS-485. The Digi One, the Lantronix -IAP devices, and several others do this.

You specified "without protocol conversion", and I'm not sure if you are referring to encapsulation or to something else. Tell us more.

hi Everyone thanks for your answer

Hi Ken,
I used Modicon M340 PLC, yes I mean encapsulation of the data through the gateway. After checking the datasheet, my device actually have RS-485 interface (such as 9600 baud 8N1) but not used modbus protocol, it has own protocol named "block-oriented single master protocol". Is there a gateway that able to convert any protocol to modbus/tcp protocol?

This sounds like the same issue that you were discussing on this other thread.

http://www.plctalk.net/qanda/showthread.php?t=64523

Are these devices Bartec RLW leak monitors ?

You need to know more about the Bartec device protocol before you can select a protocol bridge.

hi ken, yes these devices are Bartec RLW monitors, have you experience with this before?
I've read the bartec data communication manual for several times, but I still confuse how to build the communication between PLC and RLW.

like what I mention on the other thread, I should send the telegram with the right order, if I send with the wrong check sum the RLW wont response to the request.

what in my mind is: if I used DATA_EXCH block, put the request telegram on the DATA_TO_SEND of the block and then send it to the RLW without protocol conversion, then the RLW will give response to the PLC by putting the data on "RECEIVE" of the DATA_EXCH block. so that I asked: is there a gateway that encapsulate the telegram (that I send using DATA_EXCH block).
I'm really stuck in here and need more references, hope someone can give me a clue or step so that I could build this communication. Thank you

Thank you for posting that manual !

It looks like these Bartec devices have a proprietary protocol that is similar to Modbus in its basic structure, but different enough to not be a common Modbus variant (Enron Modbus and Daniels Modbus are common variants).

Now I understand why you want "encapsulation without protocol conversion", so you are essentially sending a binary string of characters out the Ethernet port, to be repeated exactly on the Serial side.

Unfortunately I am not familiar at all with the Modicon M340 controller. In your other thread, Robert Jones sounded like he understood the M340's communications configuration well.

One approach to this issue of Ethernet encapsulation might be to use two Ethernet/Serial converters. The Modicon M340 controller could use one of its serial ports in "Character Mode" to send a string of data to the first Ethernet/Serial converter, which would then encapsulate the data and send it over the Ethernet network to another Ethernet/Serial converter which would un-encapsulate it and send it out the serial port.

This is called a "nailed up" or "tunneling" connection. Many Ethernet/Serial devices support such a feature, even in the simplest non-industrial models.

What is the exact model of Ethernet/Serial device you are using ?

As posted in the other thread, the M340 does not do generic Ethernet, ASCII or otherwise. You can pack data into a DATA_EXCH block, but the restrictions will likely kill you. The Redlion products should do this just fine:

Generic Device <---> Redlion <----> M340 with ModbusTCP
RS485 RS485 Ethernet Ethernet

In the Redlion, you would use two drivers:

1. ModbusTCP slave, so you can IOScanner (with an BMXNOE0100, BMXNOE0110, or BMXNOC0401) or DATA_EXCH (or variant) with the processor port and read data from the Redlion
2. Raw TCP Active linked to a user program which implements the special protocol you need and puts the data into the ModbusTCP tags so they are available to the M340. I can send you an example of this if it helps. Or, use the serial port on the Redlion Data Station device and connect directly using serial, so use the Raw serial port driver on the RS485 port.

I think the other devices suggested in this and other threads will do the job too - I am just more familiar with Redlion products and have several installations using the raw drivers running for years without issue (both serial an Ethernet).

To answer your other question about ASCII from the other thread: my use of the term ASCII is probably incorrect, though in the end I mean the same thing. Through an ASCII table, I would translate the ASCII characters into hex numbers and then transmit the numbers. If this protocol is just hex numbers already, all the better as it is less work to do the translation (a modest savings of effort).

Hi guys Thank you very much for the quick respond,

@KEn : you've got exactly what I mean, Now I have an alternative way which is used the serial port of modicon M340 in "character mode". but is it character mode able to handle more than 1 slave? because I see from the serial link manual, its a point to point mode of data exchange between two entities. But I don't know if I used gateway it could work or not for several slaves.
has anyone experience this before?
The Ethernet/Serial device that I used is PC-E Brainchild http://www.nokeval.com/products.php?product_id=678&mid=8&sid=63&language=english
it said in the manual it has transparent mode, may be its the "tunneling" connection as you've said. But I'm still not sure.

@Robert Jones:
Hi Robert Jones, I've read manual of the Red lion gateway and download the software crimson 2.0. I still learn how to used this gateway. It would be helpful if you can send me the example as you said.
By the way do you have experience with character mode of the modicon M340?
I'm looking the alternative so I can reduce the cost. if it cannot I may move to Red Lion gateway.

I sent you a PM so I can forward along a Redlion Crimson sample. Why not use Crimson 3? You should check out the RTA automation devices as well.

I prefer to stick to Ethernet, so I do not have direct experience with the serial port in this manner. For my time and effort, it is faster for me to go with another solution because I would use IOScanner (which is ModbusTCP) to read data from the Gateway device (Redlion or otherwise) and this requires no user code. If I use the serial port, I need my own code to manage the message blocks. It's not hard, just harder than with IOScanner.

You can find a Moxa or Digi ethernet to rs485 converter for a fair price that will help. We use them as a link from our servers to outlaying devices over a radio network.

Hello, here is an article about Modbus data over ethernet that I've found

Have anybody tested this software?

The easiest way to do so, is using an RTU / PLC that already is capable of communicating over Ethernet and has the Modbus protocol.

I will throw a product that we distribute in the ring for consideration. Triangle Research offers an Ethernet enabled PLC with Modbus TCP / IP.

There are three different versions, so any decision would be based on the number and type of I/O you would require.

http://www.eternity-sales.com/tri-plc/tri-plc.htm

Disclosure - ESI is an authorized Triangle Research distributor.