Recommendations for Making Custom Cable for a 2- and 4-Wire Transmission with RS-485

Updated May 7, 2018

Reported In

Hardware

  • Serial Interface Device
  • Serial Cable

Software

  • LabVIEW

Driver

  • NI-Serial

Issue Details

I am working with a Serial interface device using RS-485 protocol to use a third-party device with LabVIEW. Do National Instruments provide some recommendations to make the connection between both devices?

Solution

1. Check the pinout of your National Instruments serial interface device available on SPECIFICATIONS AND FEATURES GUIDE NI Serial Hardware.

2. Based on the 485 mode protocol, you must properly terminate the line to prevent reflections. For this reason you must use Termination Resistors and Bias Resistors as suggested in the document Serial Troubleshooting Wizard
Is important to consider that, no National Instruments serial interfaces have built in termination resistors, but some do have built in bias resistors. To check what devices include bias resistors use the document Interfaces with Built In Termination and Bias Resistors in RS-485/422
National Instruments provides a termination adapter with the necessary 120 Ω resistors (part number 182844-01). This adapter provides the termination necessary for all 485 modes (2-wire and 4-wire).

Additional Information


 

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