1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

1A

1Y

1Z

G

2Z

2Y

2A

GND

4A

4Y

4Z

G

3Z

3Y

3A

Input 1 Signal

Output 1

Differential Pair

Input 2 Signal

Output 2

Differential Pair

Output 4

Differential Pair

Input 4 Signal

Output 3

Differential Pair

Input 3 Signal

Active Low Enable Signal

0.1 PF

Copyright © 2016, Texas Instruments Incorporated

12

AM26C31

SLLS103O – DECEMBER 1990 – REVISED JUNE 2016

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Copyright © 1990–2016, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

When designing a system that uses drivers, receivers, and transceivers that comply with RS-422, proper cable

termination is essential for highly reliable applications with reduced reflections in the transmission line. Because

RS-422 allows only one driver on the bus, if termination is used, it is placed only at the end of the cable near the

last receiver. Factors to consider when determining the type of termination usually are performance requirements

of the application and the ever-present factor, cost. The different types of termination techniques discussed are

unterminated lines, parallel termination, AC termination, and multipoint termination. For laboratory experiments,

100 feet of 100-Ω, 24-AWG, twisted-pair cable (Bertek) was used. A single driver and receiver, TI AM26C31C

and AM26C32C, respectively, were tested at room temperature with a 5-V supply voltage. To show voltage

waveforms related to transmission-line reflections, the first plot shows output waveforms from the driver at the

start of the cable (A/B); the second plot shows input waveforms to the receiver at the far end of the cable (Y).

9.2 Typical Application

Figure 8. Differential Terminated Configuration With All Channels and Active Low Enable Used

9.2.1 Design Requirements

Resistor and capacitor (if used) termination values are shown for each laboratory experiment, but vary from

Zo, of the cable and can vary from about 80 Ω to 120 Ω.