Use MB+ MSTR to query exact type of remote PLC


Thread Starter

Big Show

I am trying to build a little Modbus Plus network monitor using a Momentum IEC processor. Is it possible to use the MB+ MSTR block to query the exact type of a remote PLC (or use deduction based on the "get remote statistics" operation)? If so, can I have a few pointers on how to do it?

For example, when you use Concept to connect to a PLC over MB+, the dialog window tells you exactly what kinds of devices are on the network.

I tried googling and searching, but my search terms didn't find anything useful.

I believe what you are trying is impossible to do with a momentum, or any other plc for that fact. Concept is using a different function code (one for programming) within the modbus protocol than the ones that are supported by plcs, when the plc is to be the master. "": may be helpful to you in verifying this.

Jean-Pierre Mondange

Using MBP_MSTR, with the get remote diagnostic sub-function, you are able to identify the type of a Modbus Plus target equipment (first word of returned data)

Of course, for the equipments populating a network, you are supposed to know the adresses of these existing equipements. Otherwise you should possibly use the words indicating the active stations, returned by MBP_MSTR

I'm not convinced MBP_MSTR function block could be run in a ST section
If you're interested, I could send you an .ASC file showing the use of MBP_MSTR, integrated in a DFB. So this one could be in turn instanciated in a loop, on a ST section, in order to scan the network, rather than having to program 63 instances

my email: [email protected]

I have already figured out that the returned data of the "get remote statistics" command returns the _type_ of MB+ node, however I was hoping that I could somehow glean more detailed information (for example, the exact type of processor).

Funny you should mention ST, because initially that's what I was trying to do:
program a MBP_MSTR in an FBD section and then use an ST section to configure the block and run the loop. However, I had some difficulty, so currently, until I get it all working, I am using all FBD with a CTU block to simulate a loop. It's actually working now, I am just trying to concentrate all of the network data. (i am only collecting the first 5 status words of each node...this may change.)

According to the documentation that I read, the MBP_MSTR can't be used in an ST section, and it was my understanding that you can't put this block in a DFB either.

I am interested in your programming example, if only as a sanity check to what I have already done.

Thanks for the response!!