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Modbus Bidirectional Communication

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  • beerygaz
    replied
    This depends a lot on your host hardware, network latency and the IP->Modbus gateway. My suggestion would be to install the trial of the plugin and then slowly reduce the poll times and keep an eye on performance.

    Leave a comment:


  • salasidis
    replied
    That is unfortunate, as it would require the plugin to constantly poll and write info into the OPC server. I guess it could still be done, but overhead may become an issue.

    Is there an amount of CPU utilization that would be expected from writing 50 variables, and reading 50 variables (16 bit) every 50 mS.

    Is this feasible with the current hardware, while not affecting HMI functions too much?

    Leave a comment:


  • beerygaz
    replied
    The plugin does not act as a modbus slave, so it must initiate all of the communication and updates. It is designed to poll the slave devices on a regular interval and either read or write registers. It will not expose HS3 devices as modbus registers/coils.

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  • salasidis
    replied
    My other option is to use an OPC server - which I have available, and is what I use to communicate between the PLC and Labview.

    The PLC is connected to the OPC - and any variable changed in the PLC are updated at about 100mS intervals or so (but could be faster) in the OPC server. This happens bidirectionally, as any variable changes initiated by Labview to the OPC - are then updated in the PLC.

    Would the plugin be able to work in that way as well - connect to the OPC server, expose different devices as Modbus addresses, and then any changes in the variables in the OPC would be updated automatically in the Z-Wave side, while being available to all the other devices connected to the OPC server.

    There is a little more latency this way, but it does make the programming easier.

    Final question - presumably variable discovery / setup is not automatic, and would have to be defined within the plugin?

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  • salasidis
    replied
    By bidirectional, my concern is whether the communication can be initiated by either side.

    For example, if the PLC demands to set an output on the Z-wave network, can it do so with minimal latency, while at the same time the z-wave network can set an output on the PLC Modbus network.

    On the PLC, I can create a timer interval based MODBUS read, that would wait for an input from outside to service it, and the latency would be based on the timer interval between the reads (nothing too critical, so if kept in the order of 5-10 mS it should be acceptable in terms of response time).

    Can the plug in do the same in the reverse direction - receive requests from the PLC to change outputs, or read sensor inputs with minimal latency?

    Thanks

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  • beerygaz
    replied
    In essence the plugin becomes the master and speaks to an IP or RS232/485 device that is a slave directly or a gateway to the slave devices.
    What you're trying to achieve with your PLC should be feasible with the plugin. Post any challenges or questions you might have here.

    Leave a comment:


  • wadesready
    replied
    Originally posted by salasidis View Post
    I would like to use a PRC3000 (Automastion direct PLC). I saw in another thread that a DL06 was successfully connected with MODBUS/IP.

    In particular, I would like to be able to use the PLC to act as both master and slave. Is this possible?

    The goal it to use events in the PLC to control certain devices, as well as to use events (usually HMI initiated) to control outputs connected to the PLC.

    Thanks for any help

    yeah you can use modbus to read and write values if that is what you mean by bidirectional.... however I have not clue about PLC...or HMI....or DL06 for that matter . I use modbus with a tweek to read values from my solar charge controller, then using the values to make chit happen... In modbus Plugin the master is the device (like my charge controller) and the slave is a specific address (like 4115) from which I want to get a value

    Leave a comment:


  • salasidis
    started a topic Modbus Bidirectional Communication

    Modbus Bidirectional Communication

    I would like to use a PRC3000 (Automastion direct PLC). I saw in another thread that a DL06 was successfully connected with MODBUS/IP.

    In particular, I would like to be able to use the PLC to act as both master and slave. Is this possible?

    The goal it to use events in the PLC to control certain devices, as well as to use events (usually HMI initiated) to control outputs connected to the PLC.

    Thanks for any help
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