trying to use modbus communication


hello
i'm trying to use LG frequncy inverter ( see :
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with
unitronics PLC ( see
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but i didn't managed to connect betwean them( both have MODBUS ) can
someonu tell me what should i do?
regards
eli
Reply to
elitkh
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Get a breakout box, and make sure your signals are going where they are supposed to. I don't know your experience level, but make sure that you have one DTE, and one DCE. Make sure your handshaking is set up properly (point to point is usually disabled). Once you have all that figured out for sure, if your still not talking get some software that can simulate a Master or Slave (MdBus is one), and see if you can talk to each device. Other than that I guess a protocol analyzer would sit in between and you could see who is sending what type of packets. If you know what a Modbus packet looks like, you can use a generic protocol analyzer that just tells you the bits going through in Hex format. If you're not familiar with it, you may want a modbus specific one ($$$). One thing to consider - not all devices use all function codes. I have found some pieces equipment that cannot force multiple coils, and will only accept a force single coil for example. Make sure you're sending function codes that both devices are familiar with...
Curtis
Reply to
Curtis

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