MODBUS TCP Advice Needed

Let me start by giving my background of Modbus ----



NONE!!!!!!



My customer's plant is entirely AB. We are in the process of putting in a new production line, which includes a new spiral freezer. The freezer is controlled a Compact Logix L42. The compressors and chillers are all controlled by proprietary micro processors, which are capable of talking Modbus-TCP. The customer would like the alarms for the Micro processors to be integrated into the plants building control/utilities HMI, which is an RSView32 application. The Compact Logix will be on the same Ethernet network as the RSView application, so I am planning on using that to transfer the data.



I have purchased the following card from Prosoft.

http://prosoft-technology.com/content/view/full/6458



From what I have read on this module, it should work for my application. My question pertains to the network infrastructure. Does Modbus TCP require any special hardware or wiring, or is it very similar to AB's Ethernet/IP? Do I need a managed switch, or will any switch work? Does CAT6-E work for media? My network will consist of the Prosoft card and 4 micro processors. I am planning on setting this up as its own network, keeping it segregated from my Ethernet/IP network.



Any advice will be greatly appreciated.

Does Modbus TCP require any special hardware or wiring

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No. Modbus TCP is a software protocol which runs over regular Ethernet. A network card and an RJ45 cable, that is all.

Do I need a managed switch, or will any switch work?

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Modbus TCP is not very fast and is not deterministic to do a real-time communicatins over it. Therefore, an ordinary switch will do.

Does CAT6-E work for media?

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Yes. CAT5 would work as well.

I am planning on setting this up as its own network, keeping it segregated from my Ethernet/IP network.

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This is a good idea, not because of Modbus TCP, but rather to make sure nothing interfers with your Ethernet/IP performance. Modbus TCP doesn't really care - it is not real-time, is is just a TCP socket communications encoded in a certain way.

I am attaching my standard Modbus TCP reference file. You may not need it when using Prosoft module but it would not hurt for general understanding. Two Modbus commands - 03hex (read multiple registers) and 10hex (write multiple registers) usually cover most of everyone's needs. Remember, any Modbus implementation usually have two limitations designed in: you cannot access output memory (only inputs and internal registers) and you cannot read more that 125 16-bit words in a single communication cycle.

Why not just let the hmi read directly from the micros, if the AB doesn't need the data, I can't see a reason for the prosoft module.

GeoffC said:

Why not just let the hmi read directly from the micros, if the AB doesn't need the data, I can't see a reason for the prosoft module.

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The HMI is on a plant-wide Ethernet network, and I do not want to put the micro processors on that network. The micros will be on their own "island" network. Therefore I am using the Compact as a bridge or data server.

LadderLogic - Thanks for the info - very helpful!