Few Modbus TCP Master's in same Ethernet Adapter

e.kislov
2019-04-01
2020-01-23
  • e.kislov

    e.kislov - 2019-04-01

    Hi.
    As we know, there is some limits for Modbus TCP Slave quantity under Modbus TCP Master - 32 devices (64 since SP13).
    I have many devices and as workaround I use many Modbus TCP Masters with 32 devices in each of them.
    Seems like it works but I want to understand it this correct solution or potentially dangerous?

     
  • dFx

    dFx - 2019-04-01

    As modbus TCP relies on TCP, the only limit I see is from IP addressing/subnets.
    Standard modbus applies only if your communication is in between modbus RTU/TCP gateways (so you need the use of the slave identifier, which is 0-254).

     
  • e.kislov

    e.kislov - 2019-04-01

    Thanks. Honestly it's obvious.
    If there were no restriction (or 247 as upper limit) for slaves in Modbus TCP Master - I would have no questions.
    But my question not about specification Modbus TCP or TCP, I just wonder is this correct to use many Modbus TCP Master under same Ethernet Adapter node.
    Maybe it's unexpected-from-user solution and it will create problems for IO-drivers or something other...
    So I just want to get some advice from developers.

     
  • Ulvis

    Ulvis - 2020-01-22

    e.kislov hat geschrieben:
    Thanks. Honestly it's obvious.
    If there were no restriction (or 247 as upper limit) for slaves in Modbus TCP Master - I would have no questions.
    But my question not about specification Modbus TCP or TCP, I just wonder is this correct to use many Modbus TCP Master under same Ethernet Adapter node.
    Maybe it's unexpected-from-user solution and it will create problems for IO-drivers or something other...
    So I just want to get some advice from developers.

    Whooa,no response from Dev?
    I have a simmilar newbie question…..
    How many slaves/channels can be assigned to a Codesys device ?
    (Docs and googling did not reveal this in a second or two.)

    From the above posts I get hint of 64 slaves per master.
    Multipple masters are possible.
    But how many channels per slave?
    And what is the total max? Depending on system memory or what?
    Probably a number that will fit in a ip subnet of 200+ device will be sufficient. Then again there may be multipple device ids behind an ip.
    Anyone?

     
  • e.kislov

    e.kislov - 2020-01-23

    Ulvis hat geschrieben:
    But how many channels per slave?

    Max. 100 channels per slave

     
  • Ulvis

    Ulvis - 2020-01-23

    e.kislov hat geschrieben:
    Max. 100 channels per slave

    So... 64 slaves x 100 channels = 6.400 channels per Master ?

    (1 channel ==1 read or 1 write telegram)

     
  • e.kislov

    e.kislov - 2020-01-23

    Yes.

     

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