Can Modbus+ be Converted?

Hello All,

I love the forum it has helped me many times.

However, this time I cannot find anything on this topic.

I have a few different types of PLCs I work with.

SLC 5/01,3,4,5
Micrologix 1000
Modicon Quantum

I can communicate with the ABs via a DH-485 to RS-232 converter.

However, on the Modicon the only com ports I have is Modbus or Modbus+.

Can Modbus be converted to an RS232 or a 485 and will it work with the Concept 2.5?

Been looking for the info but I can't find anything.

Any help is appreciated.

Thanks

You're mixing some apples with your oranges here.

RS232 and RS485 are electrical standards. They define the types of signals and the voltage levels for serial communicatations. There are electrical devices to convert between RS232 and RS485. If you do a Google search for RS232 or RS485, you'll find hundreds of pages with detailed information.

Modbus, Modbus+, DH, DH+, and DH485 are communications protocols. They define the rules that two devices must follow in order to be able to communicate with each other. Think of the protocol as a language like English or French. DH, DH+, and DH485 are proprietary Allen-Bradley protocols. Modbus is a non-proprietary protocol. Modbus+ is, I believe, proprietary.

In order for your SLC to communicate with your Quantum, you must first decide on the electrical standard (RS232 or RS485). Then you must decide on the protocol. Both devices need to be using the same protocol.

Someone with more detailed knowledge of AB products than I will have to advise you on which, if any SLC or Micrologix models can use Modbus. Someone with Modicon expertise will have to comment on what the Quantum offers for communications protocol options.

Modbus is quite frequently the common protocol available on multiple brands. The details of the protocol are in the public domain, so anyone can write a Modbus communications driver without having to pay royalties to Modicon.

There is Ethernet...both support and work with Ethernet

I will lgive some one else a chance to explain this.

rsdoran said:

There is Ethernet...both support and work with Ethernet

Click to expand...

Does this mean the Modicon's and AB's can talk to each other over Ethernet?

caps00us, it is not clear to mean if you mean from PLC to PLC or from PLC to PC then back to a PLC.

Ok Peter , I will try...

Ethernet represent the physical- and data link-layer of the OSI model (layer 1 and 2).
This implys that 2 devices with Ethernet only have the same physical- and data link layer.

TCP/IP use ethernet as physical network. (Instead of ethernet it could have been: Token Ring, SLIP, PPP etc)

If 2 devices have TCP/IP (or UDP/IP) and ethernet, does this mean that they can talk??

No.

If ethernet represent the mailman and the envelope, TCP/IP represent the letter, both the sender and the receiver have to speak the same language (=application layer) if the letter shall be understood.

TCP/IP and ethernet only bring a data-packet from one application to another. If the TCP/UDP-data is a PLC protocol both PLC's understand, then they can communicate through ethernet.

Excellent up to ....

kalle said:

Ok Peter , I will try...

Ethernet represent the physical- and data link-layer of the OSI model (layer 1 and 2).
This implys that 2 devices with Ethernet only have the same physical- and data link layer.

TCP/IP use ethernet as physical network. (Instead of ethernet it could have been: Token Ring, SLIP, PPP etc)

If 2 devices have TCP/IP (or UDP/IP) and ethernet, does this mean that they can talk??

No.

Click to expand...

Here.

kalle said:

If ethernet represent the mailman and the envelope, TCP/IP represent the letter, both the sender and the receiver have to speak the same language (=application layer) if the letter shall be understood.

TCP/IP and ethernet only bring a data-packet from one application to another. If the TCP/UDP-data is a PLC protocol both PLC's understand, then they can communicate through ethernet.

Click to expand...

This leads one to believe that two Ethernet devices only need to be compatible up to the transport layer ( TCP or UDP ) which is not enough. This would allow any two PLCs that use TCP/IP to communicate which isn't true. There is more to the answer.

Hi Peter

If the 2 devices are compatible up to the transport layer (TCP or UDP) and the server socket number is known, then they should be able to connect.

But as i wrote, the TCP-data or UDP-data (the data-part inside a TCP telegram) have to be understood by both sides.
If this data is a PLC protocol like modbus, and both side can communicate with modbus over ethernet, yes then they should be able to communicate.

TCP/IP communication is a complex subject where many details have to be in order. I haven't dug that deep inside so feel to enligheten me..

My favorite brand (no name mentioned) have in addition to its own brand spesific protocol (using UDP/IP), also a open data mode.
The user can implement his own application on the application layer.
Modbus isn't implementet as a firmware-protocol for this PLC, but with use of the open data mode, this PLC can communicate with modbus over ethernet. (A guy have already written the applicationcode-protocol for Modbus/TCP as Fboxes (macro's))

Have to go

regards
karl egil liaset

OK,

I guess I started a pretty good discussion here. I can see you folks know this waaayyyy more than I do.

What I wanted to do was link PC-Quantum possible with what I have already.

I believe modbus is a serial link....haven't worked with it alot, anyway I figured one serial link could be converted. Maybe BlackBox or Automation Direct might have something, but I couldn't find anything.

Oh, by the way thanks for all of the info.

I suggest you get the Modicon Modbus Protocol Reference Manualhttp://www.modicon.com/85256BF4002683D2/all/852566B70073220C85256752006EA537/$File/PI_MBUS_300.pdf

The Modbus port is an RS232 port but I am not sure of the cable configuration. The simple answer to your question is yes, Concept will connect via RS232 to the modbus port with the proper cable.

I suggest also obtaining the manual for Concept 2.5:
http://www.modicon.com/85256AE8006D7893/all/852566B70073220C85256A490054461A!OpenDocument
Its in 3 parts.

I may have misunderstood the original question, I thought you wanted to connect all together. As far as I know Modbus uses 2 modes, RTU or ASCII and the SLC's can also work with those. I know some panelviews can work with Modbus. I stated Ethernet because they both will work on that but I have not attempted to do it, I believe it would be possible with ASCII to communicate...I have not done it so can not state specifics.

I personally dont care much for Modicon so tend to avoid them like the plague but I kind of have to deal with them from time to time.

The application layers must be the same.

kalle said:

Hi Peter

If the 2 devices are compatible up to the transport layer (TCP or UDP) and the server socket number is known, then they should be able to connect.

But as i wrote, the TCP-data or UDP-data (the data-part inside a TCP telegram) have to be understood by both sides.
If this data is a PLC protocol like modbus, and both side can communicate with modbus over ethernet, yes then they should be able to communicate.

Click to expand...

That's it! The two devices must also use the same application layer.
I know your diagram showed the application layer, but you didn't say this need to be the same.

Here partial list:

Modicon uses Modbus/TCP.
Rockwell uses Ethernet/IP and the older CSP for SLCs and PLC5s
Omron uses FINS.
Siemens S7s use ISO or ISO on TCP/IP.
The SIMatic TIs uses CAMP. I believe there is also a E-net module that allows them to use ISO so they can communicate with a S&.
Automation Direct sends raw Ethernet packets. It can respond to UDP/IP packets from a PC.

Ethernet is truely a 'Wire of Babel'.

Originally posted by caps00us

What I wanted to do was link PC-Quantum possible...

Click to expand...

Yes, but then why bring up the AB plcs? Your question isn't clear.

Originally posted by caps00us

..with what I have already.

Click to expand...

Yes, you can connect the Quantum to the PC using Ethernet, Modbus Plus or using a serial port ( Modbus ). You would need another driver for the Quantum connection. The second part leads me to believe that you already have the AB PLCs connect to a PC.

It is possible to communicate over Ethernet using several different application layers at the same time.

Protocol Converters

All the above (including the confusions and inaccuracies) are why a company called Prosoft created a Modbus Plus communication module to fit into a SLC rack.

See them at http://www.prosoft-technology.com

For a different approach, you can also use SST's excellent X-link product. With that, you insert two ISA-bus scanners cards (like a KT card and a SA85 card) into their magic box and map some virtual registers (e.g., B3:0 <==> 100000, N7:0 <==> 300000). To the SLC, the X-link "looks" like a PLC which it can read/write addresses using MSG blocks. To the Quantum, it looks like another Modbus Plus node.

Check it out at http://www.mysst.com/xlink/content.asp

A third approach I've seen used is to make the SCADA node into a protocol translator. The SCADA can be connected to both networks (whther on the same ethernet network or a different one), and will poll each system into it's internal tag database. Depending on the SCADA chosen, one tag which reads one protocol's data can write to another tag which is mapped to the other's memory address.

It's kludgy, but it's cheap (if you already have the SCADA and a large enough tag licence).

There are a lot of ways to skin that cat over a serial network. I have used the Prosoft crd mentioned above, and it works well but I found it to be slow. Another trick we have played with incompatible PLCs on serial links (AutomationDirect to OMRON) is using two EXOR opertor interfaces as communications bridges. You connect the two EXORs with their Uninet, connect each to their own PLC, and transfer the data that way. It worked well, and was easier to set up than I thought.

I believe modbus is a serial link....haven't worked with it alot, anyway I figured one serial link could be converted. Maybe BlackBox or Automation Direct might have something, but I couldn't find anything.

What I wanted to do was link PC-Quantum possible with what I have already.



If I understand what you are asking, not to get two different PLCs
to communicate but to get a PC to communicate with the Quantum.
Modbus is a serial-232 Comm link.
And if you need to go further than 50' Black Box makes a
micro line driver that converts to RS485.