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DoMore Modbus issue

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  • DoMore Modbus issue

    Hi. I have been using the DoMore in Modbus communications for years. I seldom have an issue with communications that cannot be readily solved...until this week. I started with an MB Gateway and then switched to an FA-ISOCON thinking that my used gateway might have issues. The ISOCON is new.
    I have everything set up for baud-rate, data and stop/parity that I've always used. I am communicating with Kraft rectifiers that I have worked with without serious issue for years. I've tested cable continuity, polarity, shielding. I swapped parts from other rectifiers. I've reduced the baud-rate. I cannot get the rectifiers to respond.
    Is there a feature in DoMore that would allow me to see what it is 'seeing' that is telling it that the remote is not responding? The rectifiers controller is showing communications via a blinking comms LED so it IS seeing the comms. It is simply failing to respond. (And YES, the addresses are correct.)
    Any Ideas.

  • #2
    I'm not fully understanding your configuration. Who is the master and who is the slave?


    • #3
      Are the Kraft's pulse and/or pulse & reverse? Those are the only ones I ever controlled via serial; not sure if they make normal rectifiers too or not.

      If they are pulse and/or reverse, maybe an electrical noise issue from all the current edges? How close is the serial cable to the DC cables? Are the DC cables twisted per Kraft spec? That might make a little difference.

      I also remember a non-documented "feature" with those rectifiers, though it doesn't sound as if this is probably your issue. There was something about a packet terminator. The specs said they terminated with a 254 or wanted yours to terminate with a 254 or something, but I found they (only sometimes, IIRC) wanted/used a 251 or something like that, so I had to alter my program accordingly. (CTI BASIC module for the TI 5x5; that really brings back the memories)

      As far as reading the comms, try putting a PC running terminal software on the link, and read the packets. Remember to use a terminal that will let you see the hex, or if the problem is in the non-printing char codes, you'll never see it.

      EDIT: Just noticed you said Modbus. When I was working with Kraft rectifiers, they used a proprietary ASCII command syntax, so my comments related to commissioning that type system. If you're doing Modbus, you might try an alternate master with the rectifiers, and a PC slave utility to receive the Do-More requests (and you can even still try the terminal).
      Last edited by ControlsGuy; 03-29-2016, 03:38 PM.