AN-1397
APPLICATION NOTE
One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Using the ADM3065E 50 Mbps RS-485 Transceiver in EnDat Motor Control
Encoder Applications
by Richard Anslow and Jens Sorensen
Rev. 0 | Page 1 of 10
INTRODUCTION
Motor position and angle encoders, also known as absolute
encoders, are commonly used in systems with servomechanism
drives, robotics, machine tools, and elevators. Figure 1 shows a
motor control signal chain, using RS-485 transceivers to interface
between the absolute encoder (ABS encoder) slave and industrial
servomechanism drive master for closed-loop control of an ac
motor. The ABS encoder translates mechanical motion (position
and direction) into electrical signals, which are fed back to the
servomechanism drive. The servomechanism drive provides
intelligent control of the ac motor based on the encoder
information. The RS-485 communication link between the
servomechanism drive and ABS encoder typically requires
high data rates, up to 16 MHz, and low propagation delay
timing specifications. The RS-485 cabling typically extends
to a maximum of 50 meters, but in some cases can be as long as
150 meters. In harsh industrial environments, the exposed cable
and RS-485 connectors can be exposed to harmful electromagnetic
current (EMC) events, such as international electrotechnical
commission (IEC) 61000-4-2 electrostatic discharges (ESD).
RS-485 FOR EnDat ENCODERS
This application note illustrates the benefits for EnDat motor
control encoder applications using the Analog Devices, Inc.
ADM3065E 50 Mbps (25 MHz) RS-485 transceiver. The
ADM3065E transceiver is designed for reliable operation in
harsh motor drive or encoder environments, with added noise
immunity and IEC 61000-4-2 ESD robustness as key features.
The ADM3065E timing specifications, in particular, the low
driver and receiver propagation delay, reduce system design
complexity for industrial servomechanism drive to ABS
encoders. The low propagation delay helps to reduce system
design complexity for all system clock frequencies, not only at
the high end (16 MHz) for EnDat encoders. Key benefits for
motor control applications are illustrated in this application note
using relevant application circuits and timing measurements.
RS-485
RS-485
DIGITAL SIGNAL
PROCESSING
ANALOG SIGNAL
PROCESSING
ANALOG SIGNAL
CONDITIONING
ADC
ADC
AMP
AMP
DIGITAL
APPLICATION
SPECIFIC
INTEGRATED
CIRCUIT
LDO
ADP166
ENCODER
POWER
SUPPLY
MICROPROCESSOR
ADSP-CM408F
ABS-ENCODER
INDUSTRIAL
SERVOMECHANISM
DRIVE
AC MOTOR
DIGITAL SIGNAL
PROCESSING
LONG CABLING (UP TO 150 METERS) BETWEEN THE
MASTER INDUSTRIAL SERVOMECHANISM DRIVE AND SLAVE ABS-ENCODER
DATA
CLOCK
POWER
ADA4500-2
AD7264
ADM3065EADM3065E
ADM3065E
TRANSCEIVER
TRANSCEIVER
ADM3065E
14196-001
Figure 1. Using RS-485 to Interface Between the Absolute Encoder Slave to Servomechanism Drive Master for Closed-Loop Control of an AC Motor
