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I'am trying to setup Clipper as Modbus Client on Socket 1 to poll other node (Delta Electronics DVP-SV PLC) as a modbus server.

The docs I use for it:

- New Modbus Definition & Design.doc

- Delta Tau ModBus Supplemental Reference.PDF

- Modbus TCP training.ppt


Setup screen please see in the attachment (don't know how to insert pics direct in the text...)


I suppose after "Update Command -> Update PMAC -> Close Pewin32 -> Power cycle" modbus communication must start automatically.


But I cannot get values from server with FC3 modbus code.

I monitor RHX(Y):$10780 words with Watch window (as PMAC Reference is 0) but nothing changes when I change values on server (in PLC from other shell).


It is suspicious, that all Modbus Status Counters are zero.

Is it normal?

Global Status bit 8 (Modbus Actve) is 1.


Any ideas, what I'm doing wrong?


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1. Modbus Reference # in this setup starts from 0 as opposed to Modbus numbering which starts from 1.

For example, Modbus-server memory word D512 has internal address 0x1200, so I set Modbus Reference # to 4608, which is decimal representation of 0x1200.

Is this right way?


2. Do you have Modbus cnt counter increment when you click the Refresh Counters button in the Modbus Setup page?

No I have not. Modbus cnt is always 0 regardless of actions Refresh Counters, Start/Stop/Reinitialize Command List...

I suppose Modbus cnt must increment regardless of server responces or even server existence...


Pewin32 Menu View-> Specialized Buffers show "-------" as Actual Size.

See picture in the attachment. What should it indicate when buffer has data?


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1. Since I don't know exactly how the memory map vs Modbus reference number on Delta Electronics DVP-SV PLC works, but you need to find what Modbus register number the address 0x1200 is representing. For example if this address represents the register n in Modbus addressing, then set the Modbus Reference Number to n-1 in PEWIN32PRO2 Modbus Setup page.


2. The counter should be counting as long as the server responds to client requests. If you're not getting any response, this means either the server is not responding to the request packets from the client or the client can not resolve the server through the TCP/IP. Can you please make sure your Gateway is setup properly on PMAC side. You can see the proper setup for the Gateway in the following post, http://forums.deltatau.com/showthread.php?tid=40

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  • 2 weeks later...

Sina, thank you for your kind assistance!


Setting "0" in the last tetrad of the Gateway mask makes my modbus interconnection operational.


The same result I get when I point the right Gateway IP ( with the Gateway Mask


So my conclusion is that one need to point the right Gateway by any means:


1st way is point the right Gateway IP, e.g. with the mask, which result in targeting single node - Gateway.


2nd way is to leave Gateway IP by default (when it is unknown), but to limit packets walking to subnet of C-class with the mask

In this case any packet which cannot be delivered directly from modbus-client to modbus-server will get to the Gateway, and then to the server.


This is my explanation of the fact, that modbus-client cannot find the server in spite of entering direct server IP in the Modbus Setup Window.


2nd way is a little bit strange, but anyway it works for me! :)

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