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Building a simple Modbus RTU

Hey everyone.


Got a task i need to do but got absolutely 0 previous experience with LabVIEW and just struggling with it. I laid out exactly what needs to be done below. Maybe somebody with more experience could help. Thanks a lot!


*Background: Trying to run 2 VFDs using myRIO which communicate through Modbus RTU to RS-485


Simple Interface:

-When start button is clicked, both VFDs are ran, both stop when same button is clicked again. (Register 1) for both vfds

-A speed dial would have -500 to +500 which would control the speed. (Register 2) for both vfds however VFD 2 would run at 2% of the speed (speed/50)

-so ideally just start/stop button and a dial of some sort


Every time myRIO sensor is triggered on connector C (DIO1/pin12 and DIO3/pin14) VFD 2 would start spinning the opposite direction. (slave 2, register 2)

Common params im using:

-Connection Type: Serial

-Com port: COM3

-Stop Bits: 1

-Parity: None

-Mode: RTU

-Baud Rate: 115200

-Flow Control: None

Optional/Idk if needed but ideally there.

-Poll Period: 100ms

-Timeout 300ms

-Retries 1

------------------unique params to each slave-----------------------


Slave Address:1

Reg 1 = 1 (Starts)

Reg 1 = 0 (Stops)

Reg 2 = -500/500 (Speed controls, negative is reverse)


Slave address: 2

Reg 1 = 1 (starts)(but copy slave 1)

Reg 1 = 0 (stops)(but once again copy slave 1)

Reg 2 = (Copy slave 1)/50   i.e. 2% speed


Included the manuals just incase.

myRIO Manual:

VFD 1 Manual:

VFD 2 Manual:




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