AN155
S
TEPPER
M
OTOR
R
EFERENCE
D
ESIGN
Introduction
Stepper motors are used in a wide variety of
applications. They are prevalent in consumer office
equipment such as printers, plotters, copiers, and
scanners. Stepper motors are also used in automotive
applications for electronic throttle control, dashboard
indicators, and climate control systems. Stepper motors
are also found in industrial equipment such as robotics,
electronic component handlers, testers, dispensers, and
other manufacturing equipment.
Stepper motors are often controlled using special
function ICs that provide limited control functionality.
Such ICs often employ a rudimentary step forward and
back interface to the microprocessor that limits system
performance. Other stepper motor systems are PC card
based and use a host PC to provide high performance
control.
In embedded systems it is much better to use a small
microcontroller to directly control the stepper motor. A
very small microcontroller such as the C8051F300 is
capable of providing a high performance motion control
solution. The microcontroller implements a linear-
velocity profile, generates the precise timing required,
and outputs the stepping pattern used to drive the
motor. The microcontroller directly drives the power
MOSFETs and no addition gate drive circuitry is
required.
The
microcontroller
also
provides
serial
communications for remote control and distributed
systems. This reference design uses a RS232 port
operating at 57600 bps. This demonstrates the
feasibility of using serial control. It is equally feasible to
use SMBus, I2C, RS485, or some more advanced
UART based network protocol. The C8051F300 is
housed in a very small form factor MLP11 package,
measuring only 3 mm square. The entire stepper motor
drive can easily be integrated onto the back of a small
stepper motor. A system with multiple motors may use a
single small microcontroller for each motor.
The C8051F300 is ideally suited for driving a stepper
motor. The small form factor lends itself to integrated
motor solutions. The on chip UART and SMBus provide
serial communication and control. The calibrated
internal oscillator eliminates the cost and pin-count of
using an external crystal, while providing an accurate
time base for high speed UART and precise motor
Rev. 1.0 1/04
timing. The low-pin count package has enough pins to
drive the stepper motor and RS232 transceiver, with two
additional I/O pins left over for special functions.
This reference design demonstrates a high
performance stepper motor system using the
C8051F300. The reference design provides for both
stand-alone demo operation and UART control. The
reference design may also be used as a platform for
stepper motor code development using the C2D two-
wire on-chip debug and Flash programming interface.
The reference design is complete with schematic, bill of
materials, printed circuit board artwork, code flowcharts,
and source code. The software is also available for
download from the Silicon Laboratories web site.
Using the Stepper Motor Reference
Design
Quick Start
The recommended stepper motor listed in the Bill of
Materials is the GBM model number 42BYG205,
available from Jameco Electronics
®
. Connect the GBM
42BYG205 stepper motor to the stepper motor
reference design using the color code shown in Table 1.
Table 1. GBM 42BYG205 Color Code
Color
red
yellow
blue
green
orange
brown
A+
Acommon
A-
B+
Bcommon
B-
Name
Connect the 9 V DC power supply to the 2.1 mm power
connection on the stepper motor reference design. Plug
the power supply into 120 VAC power source. The LED
labeled “PWR” should illuminate.
Copyright © 2004 by Silicon Laboratories
AN155-DS10
Silicon Laboratories Confidential. Information contained herein is covered under non-disclosure agreement (NDA).
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