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RS485 wiring and communication


Hi All,

I am new on using RS485 and years of using NI cRIO.

My target is to use cRIO-9066\ cRIO-9067 with NI9871 to communicate with ETS UV system.

First thing I would like to do is to loop back the port 0 and port 1 of the NI9871 but I didn't get it works.

Here is my setup:

Using LabVIEW 2018 SP1 32bit, NI-RIO driver 18.5

I tailor make the RJ50 cable with pin 2,3,6,7,10 with color orange-white, orange, blue-white, blue, brown respectively and plugged into port0 of NI9871.

For the other end, 2,3,6,7,10 with color blue-white, blue, orange-white, orange, brown respectively and plugged into port1 of NI9871.

Power of the NI9871 is connected to 12V power supply.


Attached are the project for my test by setting port 0 as slave and port 1 as master to read form the slave with the vi 'Modbus 485 Test RT'

The Modbus master read registry is always return error 56 : SubVIs.lvlib:ASCII Data Unit.lvclass:Read ADU


It seems my cable connection has problems as the error explain it is the timeout error.

I have tried with different cable connection and tried to communicate with my PC through USB to RS485 converter.

All of them failed.


Do I make anything wrong on my software or I make mistake on the cable connection?




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