EPower Modbus RTU communication with T2750/T2550

How to configure EPower communication with T2750 over Modbus RTU. EPower has gateway tables for input and output. Unfortunately tables addresses are the same (fixed in EPower). T2550 Modbus Tool does not allow to write and read from the same Modbus address. I need to read data and write commands to EPower. Any idea?
1 person has
this question
+1
Reply
  • Hi Adam. There is a workaround for this with Epower. Contact the Power Applications Manager Gregoire Quere for further advice or send me a list of the parameters you need to read and write.
  • (some HTML allowed)
    How does this make you feel?
    Add Image
    I'm

    e.g. indifferent, undecided, unconcerned kidding, amused, unsure, silly happy, confident, thankful, excited sad, anxious, confused, frustrated

  • Ian Roughsedge (Product Manager - Systems) November 21, 2012 15:22
    In this discussuon the EPower unit is the MODBUS slave and the LIN MODBUS Gateway (T2550/T2750/Eycon) is the MODBUS Master. The LIN MODBUS Gateway does allow both read and write to and from the same register, so there is no problem in principle.

    What is confusing here is that the EPower unit has the same fixed addresses for read and write data spaces in the I/O Gateway whilst allowing different data to be connected in each space. i.e. in the EPower a given read addresses (e.g. 3078) is considered a different space to the same write addresses (e.g. 3078). It is certainly the case that the LIN MODBUS Gateway does not permit this split, the LIN MODBUS Gateway enforces a rule that these same parameter appears at the same address in the read and write data spaces. But it is not correct to say that
    the LIN MODBUS Gateway "does not allow to write and read from the same Modbus address" because it does.

    The solution may be straight forward for your application. For writable data, why not simply assign the same EPower data register into the Read and Write parameters of the EPower I/O Gateway? Then the value can be read and written via the same address and both ends requirements are met. In fact this is quite sensible if considering comms efficiency because if the LIN MODBUS Gateway can read all the input data from the EPower i/O gateway as one message (read multiple registers) then the reading is efficient and the LIN MODBUS Gateway will look at the data received and only write data when it needs to (i.e. only write when EPower is different.). For data like Enable/Disable the write will only happen when the user changes the setting, for control output, perhaps under PID control that may change more often, the writes will happen more often.

    Note that the LIN MODBUS Gateway in master mode will never perform multiple writes except in the special case when writing a 32 bit register i.e. writing two consecutive 16 bit registers as a 32 bit value.

    See picture for a simple set up with a power demand being sent to EPower and a few electrical network parameters being read back.



    The corresponding LIN setup is show on the next picture.



    In a real system, it would be usual to read back the setpoint source from EPower too and make use of the PID Output track function to provide a bumpless transfer when going from the 'Not Comms Remote' setpoint modes to the 'Comms Remote' setpoint mode.
  • (some HTML allowed)
    How does this make you feel?
    Add Image
    I'm

    e.g. sad, anxious, confused, frustrated kidding, amused, unsure, silly indifferent, undecided, unconcerned happy, confident, thankful, excited

  • EMPLOYEE
    I’m thankful
    Very good explanation! This two tables in EPower confuse me. I will try to set comm. this way.
    Simply use just Input Definition and for Read/Write values also Output Definition.
    This is for Modbus RTU and Modbus TCPIP.
  • (some HTML allowed)
    How does this make you feel?
    Add Image
    I'm

    e.g. sad, anxious, confused, frustrated kidding, amused, unsure, silly indifferent, undecided, unconcerned happy, confident, thankful, excited