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Communication problem with LabView MODBUS on cRIO-9035 using serial RS-485 port

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Hi,

I'm trying to implement communication between cRIO-9035 and Kinco FD422S servo controller. I tested communication from PC using NI OPC server with USB - RS485 converter and everything works OK. The problem is in implementing communication from real-time target cRIO-9035.

I tried using LabView Modbus API from Real-Time Module as well as Modbus I/O Server and also unofficial MODBUS Library for LabVIEW. In all cases I wasn't succesfull. I hooked up an oscilloscope and find out strange distorted frames. Please advise me what could be the reason for that?


I wired RxD- with TxD- togehter as well as RxD+ with TxD+ on both ends of cable. I tried connecting and disconnecting grounds.


With Slave connected to cRIO RS-485 port:

IMG_20190717_144316.jpg

With Slave disconnected from cRIO

IMG_20190717_144842.jpg


My RT vi is like that:

modbus_crio_RT_main.PNG

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Hello,

 

I encounter the same problem, have you fixed it to the end?

 

Thanks!

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