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BOOKSHELF
Handy reference on microcomputer
interfacing & applications
Microcomputer Interfacing and Applications, M. A.
Mustafa, published January 1995 by Newnes. Soft
covers, 233 x 155mm, 456 pages. ISBN 0 7506 1752
7. Price $69.00.
This is the second edition of this
book which, in its 17 chapters, reasonably fully covers all aspects of the
operation and interfacing of micros to
the outside world.
The first chapter is pitched at the
beginner who is assumed to have
little or no knowledge of the subject.
It covers processors, storage devices,
input/output (I/O) devices, microprocessor operation, task execution and
interrupts.
Chapter two explains why external
devices may need to be connected to
a microcomputer, the methods used to
communicate with these devices and
the concept of input and output ports.
The next chapter expands on this
by discussing the need for flexibility
in and optimisation of any add-ons
that you may use. The boards which
are described are mostly for the IBM
style computer and its clones, mainly
because of the diverse range of offthe-shelf boards which have become
available for this type of computer.
Mustafa then goes on to compare
the pros and cons of interrupt versus
program controlled output. The chapter concludes with a few examples
of the decoding of external address
spaces.
Chapter four, entitled Using Digital
Input and Output Ports, begins by
showing the methods used to detect
external switch closures and includes
a discussion on switch debounce using
both hardware and software. It continues by explaining how comparators
38 Silicon Chip
can be used to indicate out of tolerance
voltages.
Hardware logic gates are covered
next, followed by an explanation of
how the various gates can be implemented in software if there are sufficient processor input lines available.
Most of the balance of the chapter is
taken up with the solutions to various
problems, using both hardware and
software approaches.
The last 10 pages of this chapter
discuss AC, inductive loads and power
factor.
Chapters five to eight cover, in great
detail, Multiplexers, Sample and Hold
circuits, and Digital to Analog (D/A)
and Analog to Digital (A/D) converters.
This information will be familiar to
the experienced hobbyist or engineer
but should prove enlightening to the
novice.
Chapter six explains how D/A
converters can be interfaced to a microprocessor and chapter seven does
the same for A/D converters. Chapter
eight details the application of several
commercial devices to the solutions of
some hypothetical problems.
The next chapter covers external
counters and timers, although most
modern micros now seem to include
these on the chip. Still it is often easier
to implement counting or timing functions in hardware using an interrupt,
than in software, as these functions
can occupy a large percentage of the
processor’s time.
Applications using several timers,
including that old favourite the 555,
are shown. Methods of measuring
frequency, time intervals and phase
shifts are examined, almost always
using external hardware to process
the input signals.
Chapter 10 diverges from micros to
discuss switching devices, although
the ultimate end is to control these
via a computer. Diodes, zeners, transistors, FETs, MOSFETs, IGBTs, SCRs,
thyris
tors, Triacs and relays are all
included in this summary.
The important subject of isolating
control circuits from the mains supply
is adequately covered.
The next chapter, titled Optical
Devices, is a continuation of the
previous one. It covers light sensing
devices such as photodiodes, photo
transistors, light dependent resistors
and light emitting devices such as
opto-couplers, light emitting diodes
(LEDs) and 7-segment LED displays.
Methods of interfacing these different
devices to micros are shown and an
explanation is given of the way LED
displays are multiplexed.
The chapter concludes with nearly nine pages which cover optical
encoders. The incremental encoder
is widely used but suffers from the
problem that it can only count pulses
but cannot give any absolute position.
To increase their usefulness, modifi
cations have been made such as an
extra output providing one pulse per
revolution at a predetermined position.
Absolute encoders overcome the
previous problems by repre
senting
each position by a unique code but
this obviously will require more input
data lines to a processor.
Chapter 12 explains how to generate
waveforms, again by utilising either
software or hardware under computer
control. Mustafa begins this chapter by
discussing the types of waveforms that
are usually generated by hardware,
then compares the pros and cons of
real time calculations versus look-up
tables. He continues with examples
of the generation of different waveforms using both digital and analog
interfaces for frequency selection. The
chapter also shows how DC offsets can
be generated and added to the output
waveform.
The 13th chapter introduces us to
microcomputer controlled robotic
mechanisms. Both analog and digital,
open and closed loop controls are
covered. While the chapter is quite
comprehensive, the robot designers
will know it all and the hobbyist is
unlikely to begin designing robots
after reading it.
Temperature measurement and
control is the heading for chapter 14.
The various types of sensors including
thermistors, thermocouples, RTDs
(resistance temperature detectors) and
semiconductors are explained.
The methods used to control the
temperature once it has been sensed
are then described. These are on/off,
pulse width, phase angle and zero
crossing switching. Some examples of
these methods are then given.
A chapter on motor control is next.
Many industrial process control systems will, as part of their task, control
the speed of a motor. As we know
there are two types of motors, DC and
Practical Guide to Satellite TV
The Practical Guide to Satellite
TV, by Garry Cratt. Pub
lished
February 1997. ISBN 0 646 30682
0. 296 x 210mm, soft covers, 116
pages. R.R.P. $39.00.
Published in February this year,
this easy-to-read book has been
compiled by one of the most experienced satellite TV installers in
Australia, Garry Cratt. It is written
in an informal style and is copiously illustrated.
Topics covered include a history
of satellite development, principles of satellite operation, earth
station components, encryption
systems, video stan
dards, video
compression (MPEG, etc), system
installation and wiring.
As you might expect, there is a
lot of information about satellite
receiver hardware such as dishes,
feedhorns, polarisers, LNBs (low
noise block converter) and so on.
There is a large glossary and 46
pages of satellite orbital data, transponder loading and footprints.
AC and they, unfortunately, require
different methods of control.
The author describes the various
types of DC motor speed control using
the computer in a closed loop system,
then other methods which use some
external hardware but don’t take as
much computer processing time.
The speed of an AC motor can be
varied by altering either the applied
voltage or the applied frequency.
While the latter is harder to implement, it is the more efficient method,
as the output torque is higher. Various
methods using voltage, frequency and
pulse width to vary the motor speed
are then described.
The penultimate chapter, headed
Miscellaneous Applications, covers
such things as interfacing a keypad to
a micro, interrupt control, DMA (direct
memory access) and handshaking. It
continues by discussing rudimentary
process control test procedures, the
provision of additional supplies to
power the external add-ons and battery
backup of these add-ons.
The final chapter talks about the
In summary, this book is down
to earth and up to date. It is available at $39.00 plus $5 postage from
Av-Comm Pty Ltd, PO Box 225,
Balgowlah, NSW 2093. Phone (02)
9949 7417; fax (02) 9949 7095.
possible limitations of an existing
computer system and the upgrade
paths available. It also describes the
limited storage of RAM and the probable need to transfer RAM data to a
hard disc. Brief mention is then made
of operating systems, programming
languages and emulators.
An emulator is a collection of hardware which allows a software program
(eg, for a microcontroller) to be loaded
into it and executed. The program
steps can be traced and intermediate
values checked to confirm the correct
operation of the program before it
is “burned” into the final device. If
“bugs” are found, the program can
be altered then run again to verify its
correct operation.
To sum up, this book is a good reference for the hobbyist or student who
wants to have a better understanding
of the topics covered. It contains lots
of worked examples to illustrate each
chapter and is an ideal starting point.
Our review copy came from Reed
International Books Australia Pty Ltd.
Phone (03) 9245 7168. (R.F.W.)
SC
April 1997 39
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