Ethrnet IP, Ethernet TCP/ip, Modbus TCP/ip

Steve_D

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Join Date
Jul 2002
Location
Albury/Wodonga
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92
Hi guys, looking for a bit of clarification here as Ethernet IP, Ethernet TCP/ip, Modbus TCP/ip seem to be interchangeable and Id like some input as to the accuracy of what I am about to say.
Ethernet IP is an ethernet protocol for mostly process equipment, i.e remote bases, VSDs etc which would require an specific ethernet IP card and third party network configuration. yes?/No?
Ethernet TCP/ip is your ordinary ethernet comms to power meters, analysers etc that have a TCP/IP connection point which you would get by connecting an ethernet port on your PLC rack to the network (and then to the device)yes?/No?
Modbus TCP/IP is a protocol on the ethernet TCP/IP system which allows you to map in data from the ethenet device as you sort of would with modbus serial but on an ethernet network. Yes? No?

Question 1, If I have a power meter with an ethernet port (it doesnt say what sort of ethernet comms so I assume its not modbus tcp/ip) that is clearly designed for a web browser connection, will I be able to connect this to my PLC ethernet card and somehow read the values into my PLC?
Apparently my PLC can handle "socket" data handling which sets up comms to ethernet devices like this but im not sure whether the device can handle socket comms, or is this ALWAYS the case for ethernet devices?

Quetsion 2, if a device is ethernet TCP/ip but doesnt specifically say modbus TCP/ip can I read the data out of it?

Really happy to be shown right or wrong.
 
Let's start with some "hand-wavy" definitions:

Ethernet is a layer 1/2 (of the OSI model) technology that essentially describes the physical connection, and message collision detection. (Not useful by itself).

Ethernet TCP/IP: Further "up" the OSI model is another layer called the "transport layer." This layer defines how a message (collection of packets) is broken up and reassembled, and how they get to their destination.

Ethernet/IP (Industrial Protocol) is an application layer implementation of Ethernet that combines with another protocol, Common Industrial Protocol (CIP). CIP is a collection of standard services and messages that a device executes/understands. CIP gives meaning to the bits/bytes in the messages.

Modbus TCP/IP: Modbus is was originally a serial communication protocol (and can still be used that way), but now can be sent along an Ethernet network because messages follow the rules of TCP/IP. With the previous definitions, Ethernet described the physical wires; TCP/IP described the transmission rules; Modbus also gives meaning for the bits/bytes contained in within the TCP/IP messages.

Ethernet/IP and Modbus TCP/IP are two cakes with similar ingredients (physical connection, transmission etc) but very different appearances or flavours -- one could be a birthday cake, another a wedding cake. Sending birthday cakes to birthday parties is one application, sending wedding cakes to a wedding is another. To the delivery driver (the Ethernet with TCP/IP), a cake is a cake.

Answer to question 1: Maybe. It depends on the communication options that were selected when it was ordered. Refer to the power meter's user manual to determine the protocols supported.

Answer to question 2: Also maybe. Ethernet TCP/IP doesn't define the application that can be used to interpret the bits.
 
Thanks for that clear reply..much clearer now, it appears I need the function organisers to tell me exactly what they are celebrating so I get the right ingredients to give them the right cake as most of them just say we need a cake!
 
I had a similar issue & had to wrap my head around modbus.

We have Siemens PAC meters dotted around site with what i was told Ethernet built in, it turned out to be Modbus TCP/IP. As i have not got a modbus card on the PLCs, i used kepware to retrieve the data from each of the units.
 
It’s worth noting that Allen Bradley equipment use two different Ethernet protocols, EtherNet/IP UDP and EtherNet/IP TCP. EtherNet/IP UDP has become the ODVA’s standard Ethernet communications protocol so it is showing up in other brands as well.
EtherNet/IP UDP is also known as “Produce/Consume” or Implicit messaging and EtherNet/IP TCP is also known as Explicit messaging.
Produce/Consume (P/C) was created as an I/O scanning protocol with very little latency. When enabled it opens a connection and keeps it open until it is either told to close or there is an error. If it closed because of an error it will automatically attempt to re-open the connection.
Explicit messaging uses message instructions and when enabled, the device doing the messaging requests a connection, opens it, exchanges the data and then closes the connection. This takes longer but it’s also more robust.
P/C is generally not recommended in wireless applications because of how sensitive it is to missing packets.
Please note that this explanation is coming from someone who knows just enough to make him dangerous. I’m sure there are some subtle points I’m missing and there are variants of these protocols.
 

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