A

D

B

Z

Status

R

D

R

D

R

D

R

AM26LS31

AM26LS32

Encoder

Interpolation

Electronics

Encoder Phase A

Encoder Phase B

Encoder Index

Status

Servo Drive

Motion Controller

Copyright © 2016, Texas Instruments Incorporated

11

AM26LS31, AM26LS31C, AM26LS31I, AM26LS31M

www.ti.com

SLLS114L – JANUARY 1979 – REVISED OCTOBER 2018

Product Folder Links: AM26LS31 AM26LS31M

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Copyright © 1979–2018, 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 or RS-485,

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. In general, RS-485 requires termination at both ends of the cable. 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. Laboratory waveforms for each termination

technique (except multipoint termination) illustrate the usefulness and robustness of RS-422 (and, indirectly, RS-

485). Similar results can be obtained if 485-compliant devices and termination techniques are used. For

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

receiver, TI AM26LS31 and AM26LS32C, respectively, were tested at room temperature with a 5-V supply

voltage. Two plots per termination technique are shown. In each plot, the top waveform is the driver input and the

bottom waveform is the receiver output. To show voltage waveforms related to transmission-line reflections, the

first plot shows output waveforms from the driver at the start of the cable; the second plot shows input waveforms

to the receiver at the far end of the cable.

9.2 Typical Application

Figure 12. Encoder Application