Interfaces with Built In Termination and Bias Resistors in RS-485/422

Publish Date: Dec 19, 2018 | 0 Ratings | 0.00 out of 5 | Print

Overview

This article discusses National Instruments RS-485/422 interfaces and built in termination and bias resistors.

Table of Contents

  1. Introduction
  2. Termination Resistors
  3. Bias Resistors
  4. Additional Resources

1. Introduction

Currently, no National Instruments serial interfaces have built in termination resistors, but some do have built in bias resistors.

 

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2. Termination Resistors

These resistors are not included because there are use cases where termination is not desired, such as when the interface is in the middle of the serial network (termination is only needed on the ends of the network).

Note: Refer to the Serial Troubleshooting Wizard: Termination and Bias Resistor Information for background information and details on termination resistors.

 

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3. Bias Resistors


Many NI RS-485/422 interfaces have built in bias resistors, and a subset of these have software configurable resistors, as shown in the chart below:

 

Hardware

RS-485
Socketed 
Bias
Resistors

RS-485
Programmatically
Controlled Bias
Resistors

PCI/NI PCIe/PXI/NI PXIe-8431 eight port and NI PXIe/NI PCIe-8431 16 port

No

No

All other PCI/PXI-8431 and PCI/PXI-8433

Yes

No

USB-485 one port

No

Yes

USB-485 two and four port

Yes

Yes

ENET-485

Yes

No

NI ExpressCard-8420

No

No

NI ExpressCard-8421

No

Yes

PCMCIA-485

No

No

NI 9871

No

No 

 

For the full hardware specifications for all NI serial interfaces, see the Serial Hardware Features section of the NI Serial Hardware Specifications and Features Guide.

Note: Refer to the Serial Troubleshooting Wizard: Termination and Bias Resistor Information for background information and details on bias resistors.

 

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4. Additional Resources

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