communication error with multiple slaves on RTU on same port

Forum Home Forums Communicating with Devices Modbus communication error with multiple slaves on RTU on same port

This topic contains 12 replies, has 2 voices, and was last updated by Avatar medvdev 3 years, 1 month ago.

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  • #1584
    Avatar
    medvdev
    Participant

    Dear Mikhail,

    Please clarify the behavior of communication lines, each communication line is a master ?? for the connected device for which it is created.

    If say for “communication line 1” virtual “com port 1” is assigned, and data polling is done at an interval of 15 minutes, then during that 15 minutes period can other communication line use the same come port 1 if assigned so, as RS 485 states that multiple slaves can be communicated through same com port on multi drop network.

    My observations are:-Communication line keep com port occupied irrespective of communication or not and other communication lines denied access to same com port even during no communication period.

    Please explain then how to utilise rs 485 feature of multi drop communication.

    Regards,

    #1585
    Mikhail
    Mikhail
    Moderator

    Please clarify the behavior of communication lines, each communication line is a master ??

    It depends on a driver (Kp*.dll). In case of Modbus it is master.

    can other communication line use the same come port 1 if assigned so

    No, it is blocked.

    Please, explain why do you need to share COM-port between different applications? Are there other approaches to solve your task?

    #1589
    Avatar
    medvdev
    Participant

    Dear Sir,

    I would like to share the same rs 485 communication line to connect with other slaves, as rs 485 allows the multi drop feature. the gateway converter that i m using install virtual com port ( say com 1) on pc then communicate with any assigned device, now as communication is on 2 wire rs 485 line i want to communicate with other devices also using features of rs 485 i.e. it support multi drop network. on same wires, but communication lines keep the com port busy all the time irrespective of it is communicating or not.

    Also one gateway (TCP to RS 485 converter) can install only one com port on pc, how to communicate with multiple devices on modbus RTU mode.

    #1590
    Mikhail
    Mikhail
    Moderator

    In this case you should add all the devices connected to RS485 to a one communication line of Communicator. It is a usual situation.

    #1591
    Avatar
    medvdev
    Participant

    Dear Sir,

    I think It will not work, consider all identical devices…. how the data address will be identified then…. is it possible to assign multiple slaves address to single communication line??

    Regards,

    #1592
    Mikhail
    Mikhail
    Moderator

    is it possible to assign multiple slaves address to single communication line?

    Yes, each device on a communication line has its own slave address.

    #1593
    Avatar
    medvdev
    Participant

    OK… but at communicator when we go to request sequence tab, there at address field only one address can be assigned to any communication line, then how is it possible to communicate with more then one devices on same communication line.

    regards,

    #1594
    Mikhail
    Mikhail
    Moderator

    Create a screenshot, please.

    #1595
    Avatar
    medvdev
    Participant

    https://postimg.org/image/jq00k97jb/ or

    [![slave addressing.jpg](https://s15.postimg.org/auz69qiqz/slave_addressing.jpg)%5D(https://postimg.org/image/jq00k97jb/)

    I think , I am not able to explain you…. agian… can a single communication line talk with multiple devices simultaneously…… if yes then where to define the address of say 4 devices connected with single communication line,

    in communicator as attached in link above only one device can be assigned to single communication line.( then how can one communication line talk with multiple devices at same time??)

    #1596
    Mikhail
    Mikhail
    Moderator

    You should add another device to the line. Use Plus button or import the device from the configuration database.

    #1597
    Avatar
    medvdev
    Participant

    How to add two device with one communication line…??? plus button add another communication line. can second device be added to same communication line which is already having one device linked with itself?

    I have tried but it is seems not possible.

    Regards,

    #1598
    Mikhail
    Mikhail
    Moderator

    Could you make a screenshot what button did you click and what result did you get?

    #1617
    Avatar
    medvdev
    Participant

    i think i got it…. trying at wrong place….nice help…. thanks.

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