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Punt Systems

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Posts posted by Punt Systems

  1. Hi Paulo,

    What you probably mean is a Machine to Machine SIM card in a router, which is nothing more than a simple mobile data connection.  That is possible, but you will need to use the listen connection of Remote Operator, program port forwarding in your local router, and initiate the (ad-hoc) outgoing connection from the PLC (Which has to be created in your ladder), probably useful for maintenance , but very limited, because somebody has to initiate it on the PLC, and if the PLC contains a PCOM password, you will need a least Remote Operator version V1.2.85.3, because you have to store the password for the listen connection. . . . . if you want a permanent ('Ethernet (Call)' ) connection,  you will need a TCP bridge (f.e. with the use of a permanent vpn) to connect the two outgoing TCP connections. Not a simple solution. but certainly possible.

    Best regards

    George

     

  2. Hi Denis,

    You are right about that . . . .

    But in the Samba for instance, there is very little space, you probably will need all the operands available (we sure do).
    Now you don't have to copy/program any duplicate operands, you will save space and time,  and also get a warning when somebody executes a Modbus write command. 
    And yes, in the V700 (space enough) we have used these duplicate values, So there is no risk (indeed),  but still we like the fact that we get a warning when somebody tries to execute an illegal Modbus write command to the PLC.

    Best regards

    George

     

  3. Although it seems a common belief that you cannot block Modbus write due to the way it’s engineered in the Unitronics PLC's, there certainly is a way to achieve this.  
     

    You have to look at SL11. where every Modbus command is processed. It looks like that the value in SL11 makes no sense at all, until you attach a “Vector fill” to it.
    Then each Modbus function becomes a specific value in MI 1240 (example). 
    After that, it’s very easy to specifically allow or block a command (both 'read' and 'write') or an entire function.

    In this specific case you can read everything, but as soon as you give a write command, it must be 1 of the 8 values, otherwise the Modbus connection is stopped immediately, to prevent anyone from being able to continue.
    After that you can decide to display or send out a warning (or whatever) 

    The only small downside to this solution is . . . .  although it will be detected (for sure) . . . . . you could still make 1 'write command' mistake (If you hit the jackpot).

    This is tested with Modbus TCP/IP only, if you have Modbus RTU, you probably will need to edit a couple of things (I did not test that yet)

    There is a timer TD 153 (example) present, because of a timing issue, when switching from one Modbus function to another, to prevent unwanted blocking of the Modbus scan.
    But if you don’t allow any Modbus write command, a timer is not needed and MB 1703 (example) can do the job for you.

    ModbusIP.thumb.png.aa1ceb3d9bf03748c852186407db1a31.png

     

    Another tip:

    For anyone who wants to use a Samba with an ethernet card and still wants to have the option of Modbus RTU or any other situation with only Modus TCP/IP supported, you can use a simple module TCP2RTU from papouch.com.

    Example ladder with TCP2RTU:

    ModbusIPTCP2RTU.thumb.png.0097dcb367cd86020678713634c7064e.png

     

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