VIPA PLC & MPI Protocol? Please help...

J.A.du Toit

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Sep 2006
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I'm currently working on a project were we use the Vipa PLC to communicate with a "Red-Lion G308" HMI Panel. The panel has the functionality to communicate via a RS-232<->MPI adaptor to a Siemens PLC. (Reading/Writing to DB's, etc...)





The Vipa PLC allows one to communicate on RS-232 via the GREEN CABLE. This means that the panel must be able to communicate to the PLC via the Green Cable.


I've managed to gather information about the 3964R protocol. With this knowledge I wrote a VB application which is between the Red-Lion Panel and the PLC, receiving the incoming messages from the panel and passing it onto the PLC. This application works wonderfully with the LAN<->MPI adapter from Vipa, so I'm confident that my application works correct! But as soon as I plug in the GREEN CABLE the PLC doesn't respond after the second packet (which looks like a initialize packet, it differs with the last to bytes in the reply too...).

Here follows the packets that I trapped. It would help quite a bit if I could understand the content of the data "MPI-Siemens" to see why the VIPA doesn't want to respond...

Time in [ms] : Hex bytes (First packets is at the end)





GREEN CABLE (NOT WORKING)


LAST PACKET


Red-Lion -> Vipa


29256031 B>:[21][80][00][00][00][10][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00]
29256031 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]


Red-Lion -> Vipa


29254265 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29254265 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Vipa -> Red-Lion


29254234 A>:[01][03][20][56][30][30][2E][36][30]
29254234 B<:[01][03][20][56][30][30][2E][36][30]



Red-Lion -> Vipa


29254187 B>:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]
29254187 A<:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]



Red-Lion -> Vipa


29251578 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29251578 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29249671 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29249671 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29248046 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29248046 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29246281 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29246281 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Vipa -> Red-Lion


29246250 A>:[01][03][20][56][30][30][2E][36][30]
29246250 B<:[01][03][20][56][30][30][2E][36][30]



Red-Lion -> Vipa


29246203 B>:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]
29246203 A<:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]



FIRST PACKET











LAN<->MPI (WORKING)


LAST PACKET


Vipa -> Red-Lion


29674109 A>:[21][00][00][00][00][00][01][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29674109 B<:[21][00][00][00][00][00][01][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29674015 B>:[21][00][00][00][00][06][01][01][00][00][03][09][00][00][00][14]
29674015 A<:[21][00][00][00][00][06][01][01][00][00][03][09][00][00][00][14]



Vipa -> Red-Lion


29673984 A>:[21][00][00][00][00][00][01][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29673984 B<:[21][00][00][00][00][00][01][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29673890 B>:[21][00][00][00][00][06][01][01][00][00][03][09][00][00][00][14]
29673890 A<:[21][00][00][00][00][06][01][01][00][00][03][09][00][00][00][14]



Vipa -> Red-Lion


29669843 A>:[21][80][00][00][00][10][10][00][01][00][00][00][07][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29669843 B<:[21][80][00][00][00][10][10][00][01][00][00][00][07][00][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Red-Lion -> Vipa


29669750 B>:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]
29669750 A<:[21][80][00][00][00][10][00][01][00][00][02][01][00][00][00][00][00][00][00][00][00][00][00][00][00][00]



Vipa -> Red-Lion


29669703 A>:[01][03][20][56][30][30][2E][38][35]
29669703 B<:[01][03][20][56][30][30][2E][38][35]



Red-Lion -> Vipa


29669546 B>:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]
29669546 A<:[01][03][02][27][00][9F][01][3C][00][90][01][14][00][00][00][02][01][1F][02][01][01][03][81]



FIRST PACKET








Your help in this matter would really be appreciated!





Thanks
Augusto
 
I apologize for my ignorance, but what is this GREEN CABLE you speak of? From a little bit of searching I see some references to it as a programming cable. If this is the case, that could be the issue. I know that a HMI MPI adapter is needed for communications, and that this adapter differs from the PC/PG MPI cable used for programming.


Regards,
 
MPI-Protocol, Vipa & Red Lion.

The GREEN CABLE is a VIPA specific feature, which may be used instead of a MPI-Adaptor. This means that you could plug the GREEN CABLE directly into the VIPA PLC (Straight RS-232) and use it as if there is an RS232<->MPI adaptor plugged-in. Step7 Simatic Manager works perfectly, without making any changes to it. (So Simatic still thinks that there exists a MPI-Adaptor).

Hope this explains it a bit. (I do apologise when I repeat, repeat stuff a bit... :)

I think that the solution to my problem would be to have just an overview/quick description of the Siemens MPI protocol, so that I can figure out why the VIPA doesn't want to respond after "initialization (I suppose)".

So any help would really be appresiated.

Thanks again, Augusto

P.S. Please explain me the differences between the two protocols you mentioned.
 
Last edited:
Hello J.A.du Toit.

You may want to talk to Thomas Hergenhahn. He is the one responsible for the excellent Libnodave comms library for S7.
http://libnodave.sourceforge.net/index.php
He can also be found as "zottel" on www.sps-forum.de.

But not sure if he know about the difference between VIPA and Siemens MPI.

There is very little MPI information available from other sources (none actually).
 
The reason Vipa accepts the Green Cable, is because the MPI port in VIPA is not only MPI but MP2I, but if the Red Lion HMI is MPI than the only cable you need is a Profibus cable with two Profibus connectors and the resistor switch in the on position on both ends.
 
The G3 is not really MPI, a MPI adapter is needed for communication between a G3 and a S7 via MPI. We support the protocol the the adapter is needed for the conversion from 232 to 485, as well as the other hardware that is needed to communicate to the PLC.

Regards,
 
The whole thing is a bit strange.

J.A. du Toit.
I've managed to gather information about the 3964R protocol. With this knowledge I wrote a VB application which is between the Red-Lion Panel and the PLC, receiving the incoming messages from the panel and passing it onto the PLC.
Are you trying to "crack" the MPI protocol or something ? I cant see what you achieve by the whole excercise.


This application works wonderfully with the LAN<->MPI adapter from Vipa,
Where do you put in the special "eavesdropping" device when you have the Ethernet/MPI adapter. I suspect the Ethernet/MPI adapter to work fundamentally different to the serial/MPI adapter.
 
With regards to "bit strange"-thing let me explain a byte:

1)Simatic Manager "speaks" MPI-Serial.
2)G308 Red Lion Panel "speaks" MPI-Serial.
(That means both needs a MPI<->RS232 adaptor. CORRECT?)
3)VIPA CPU's "speak" MPI.
4)BUT VIPA has a "Green Cable", which has no Adaptor! So communication is straight RS-232.
5)Now plug this "Green Cable" in, and program the VIPA PLC thru Simatic Manager (without making any config changes) and it works!

So it's quite simple and logical that VIPA "acts"/"functions" as an MPI-Adaptor, but clearly not to all the commands. That is the reason why I "trapped"/"Sniffed" or "whatever you want to call it" the data. And I hoped that someone that knows the protocol (Maybe in future it will be me ;)) might understand why it's not working.

I would really like to know whether anyone understands the packets, that I posted. This would be the next step forward.

The other question is why does the packets look so "Excatly" the same, except for the last two bytes in the "init"-packet (I suspect). And those two bytes, what do they mean? This must be the reason why the VIPA does not want reply.

Regards
Augusto

P.S. Thanks for your inputs, every word really helps a bit. It's always good when the same problem is viewed from more than one angle.

Oh an I forgot, the MPI<->LAN adaptor is also from VIPA. Their software creates a virual Serial Port. This means that communication is excatly the same way as to any other serial port.
 
Last edited:
You are correct in all your assumptions, as far as I know.

Are you doing this out of personal interest ?
Then try to get in contact with the Libnodave project I mentioned before. I am sure that you can get into a deep technical discussion there.

Or are you trying to solve that particular problem by yourself ?
It is a lot of effort to put in. And what can you do about it even if you should figure out the exact reason for the failing comms ?
I would contact Redlion to have them try and solve it.
 
I have sent a link to this post to the software engineer who is responsible for writing the MPI driver. I will let you know any information she can give me.

Regards,
 
As far as the data transmission you captured. The process is as follows:

- Send Init HMI Adapter Request (the Vipa is responding correctly to both scenarios)

- Send Connection Request (Vipa does not respond to with the GREEN CABLE)

We believe that the GREEN CABLE is a replacement for the PC/PG interface adapter, while our panel requires the HMI adapter, which we believe is equivalent to your LAN-MPI adapter.

There is something that the adapters do in order for programming or communications to work. As far as Siemens is concerned, there are 2 adapters one for programming and another for communications, neither one can be used for both. There is a company that makes one that can do both, but it is more expensive.

Unfortunately we are not familiar with what happens on the PLC side, we are only familiar with what we send to the adapter.

Regards,
 
As far as Siemens is concerned, there are 2 adapters one for programming and another for communications
As far as I know, there is only the one and same serial PC adapter for MPI from Siemens.
Which ones are you thinking of ?

There is a "PC adapter" for serial comms to S7.
And there is a "TS adapter" for serial comms via modem to S7.
Both can be used for programming, as well as HMI applications.
 
We have 2 differnet adapters.

6ES7 972-0CA23-0XA0 Labeled PC Adapter V5.1
6ES7 972-0CA10-0XA0 Labeled HMI Adapter

I have tried to use both for programming and both for communications. I have only been successful using the PC adapter for programming, and the HMI adapter for communications.

The only adapter that I found found which can handle both, that one of my colleagues has actually tested, is the Process-Informatik. I believe Helmholz may also make one that can be used for programming and communications.

Regards,
 
Aha, I see that the 3rd party suppliers indeed have separate PG and HMI versions of their adapters.
I cannot locate that type number from Siemens, and there is no refrence to it in the support section either, but I believe what you say.
From what it says on Proces-Informatik's website, it looks like it has to do with the connection type (programming = "PG", HMI = "OP").
Proces-Informatik also make a "universal" type.

Just one more thing to be aware of.
 
Mpi

Hi Jesper

Do you think Proces-Informatik is good cabel/adaptor for beginner with Siemens?
I do not have a clue about that.
Its 100 euro cheaper then others.
Thanks
 

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