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mjrx

Modbus to F700 series VFD

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I am trying to connect an HMI direct to a Mits F700 inverter and talk via Modbus. I can connect, and read/write to any of the parameters (41000 - 41900) with no problem. The problem starts when I try to write to any of the modbus regs that control it, namely speed/hertz value register 40014. I can read it fine, but when I try to write to it it returns an exception error. I have put aside the HMI and am using Modscan right now and I get the same thing - read OK, write doesn't go. I am tapping the data, the request goes out with function 06 (it looks just like the parameter writes) but returns 86 with a code of 03, which I think means bad data but I dont think so as I am reading a value like 4555 (which is 45.55 hz) and I try to write the same value, or even a value like 3535 it throws an exception. Anyone come accross this? I have successfully used a QJ71MB91 to write to these drives and never had any problem, and I know the 'MB91 card also uses function 06.

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I used a FX3U with the FX3U-485-BD card to communicate with the VFD inverter without problem. But I had to write to register 40013 to reach 40014 for the speed setting, due to that Modbus register addressing starts with 1 and PLC registers starts with 0. To reach the CW at 40009 did I specify 40008. Have you tried to offset your addressing with 1 ? Sorry, just checked the type of inverter I used, it was the FRD 700 for that project. But it will not surprise me if the registers are the same. I remember that I had to specify in the inverter that it should be controlled (CW) via modbus, and also that the target frequency was via modbus.

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Its not an offset issue, I've been through all that. I am aware of Param 549=1 to enable Modbus, otherwise it wouldn't work at all. I have successfully used the 485-BD card and the Q series 'MB91 to communicate with the drive. Whats stumping me, is everything works - can read/write to any parameter, read status (hz, amps, volts, etc) read any CW or control register, its just when I try to write to a control register (which are MB regs 40005 - 40015) it fails. I have reset all VFD params and started fresh with defaults thinking maybe a param was disabling it, no luck.

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Thanks for the help, I may have found the issue - I did a param all-clear and reset just the relevant params in the VFD for comms. I'm not sure which parameter was holding me up, although this VFD is a bench test unit and its always getting played around with techs testing various things (including me!)

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Hello,

i have the same problem. Did you find what is the parameter what you need change?

Luiz

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