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    How to Control VFD via RS485 Interface

    In addition to panel control and terminal control, we can also use the RS485 interface (Modbus RTU protocol) for remote control of ATO’s variable frequency drives.

    RS485 interface is quite useful for the centralized control and monitoring of equipment. This type of control plays an indispensable part in automatic industrial control.

    That's why we write this blog to illustrate how we can use the Modbus RTU protocol to control the VFD.

    We need to connect RS485 to 485+ and 485- ports for communication, and GND is optional for connection according to specific requirements. Join the interface with a USB converter.

    connect rs485 to electric poles 
    connect rs485 to USB converter

    Prior to communication, it is necessary to set the communication parameters of the VFD.
    P0.01=4(Serial port given)
    P0.03=2(Terminal control mode)
    P3.09=163(MODBUS-RTU, 1-8-1 Format, without check, 9600bps)
    P3.10=001(Local address 001)

    communication parameters setting

    Launch the test software, set the communication parameters such as serial port and baud rate, set the data input and output pattern to hexadecimal, and run the serial port.

    launch test software

    Execute write command 06 to VFD No. 01, input parameters: 01 06 20 00 00 01.
    20 00 is the execution address and 00 01 is the run command. Returning the same data indicates that the start command has been executed.

    execute write command 06

    00 07 is the stop command, and 20 01 is the frequency setting address. Set the frequency to 0F A0 (04000 in decimal, frequency 40.00Hz).
    It can be seen that the frequency of the VFD on the left has been set to 40.00Hz.

    vfd running at 40hz

    Execute the start command again, write 00 01 to the 20 00 address, and the variable frequency drive runs normally at 40.00Hz.

    reexecute start command

    Execute read command 03 to No. 01 VFD, input parameters: 01 03 21 03 00 01; 21 03 stores the current output frequency of the VFD.
    0F A0 in the returned value is the current frequency (40.00Hz).

    execute read command 03

    21 06 stores the current output voltage of the frequency converter, and 21 04 stores the current output current of the converter.
    The return value of 00 14 refers to the current output current (2.0A). We can confirm whether the current voltage and current values are correct from the panel.

    confirm the values

    00 07 executes stop command, and that’s all for the demonstration.

    You can get more details through the related video on our Youtube channel:


    ATO provides a full line of variable frequency drives for different applications. Our product cataloge covers single phase VFDs, single to three phase VFDs, 220V to 380V VFDs, 120 inpiut VFDsthree phase VFDs as well as non-enclosure VFDs with all available in a wide rated power range from as minimum as 1/2hp to the maximum 300hp. View the catalog to select the type that best fits your application!

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