Serial Port
Complete
COM Ports,
USB Virtual COM Ports,
and
Ports for Embedded Systems
Second Edition
Jan Axelson
Lakeview Research LLC
Madison, WI 53704
Serial Port Complete:
COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems
Second Edition
Jan Axelson
Copyright 1998, 1999, 2000, and 2007 by Janet L. Axelson
All rights reserved. No part of the contents of this book, except the code examples, may be
reproduced or transmitted in any form or by any means without the written permission of
the publisher. The code examples may be stored and executed in a computer system and
may be incorporated into computer programs developed by the reader.
The information, computer programs, schematic diagrams, documentation, and other
material in this book are provided “as is,” without warranty of any kind, expressed or
implied, including without limitation any warranty concerning the accuracy, adequacy, or
completeness of the material or the results obtained from using the material. Neither the
publisher nor the author shall be responsible for any claims attributable to errors, omissions,
or other inaccuracies in the material in this book. In no event shall the publisher or author
be liable for direct, indirect, special, incidental, or consequential damages in connection
with, or arising out of, the construction, performance, or other use of the materials con-
tained herein.
MPLAB, PICDEM, and PIC are registered trademarks of Microchip Technology Inc. in the
U.S.A. and other countries. Other product and company names mentioned herein may be
trademarks of their respective holders.
Published by Lakeview Research LLC, 5310 Chinook Ln., Madison WI 53704
On the web at www.Lvr.com
Distributed by Independent Publishers Group (www.ipgbook.com).
14 13 12 11 10 9 8 7 6 5 4 3 2 1
ISBN 978-1931448-07-
9
Print ISBN: 9781931448062
iii
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Advantages 2
Limits 4
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The Computers 4
The Physical Link 6
Programming 6
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Example Systems 8
Managing Communications 9
Special-purpose Modules 9
iv
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Asynchronous and Synchronous Communications 11
Word Formats 12
Bit Rate and Baud Rate 13
System Support for Low-level Protocols 14
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The Format 15
The Need for Accurate Timing 15
Autodetecting the Bit Rate 17
Autodetecting a COM Port 18
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Binary Data 18
Text Data 19
ASCII Hex 22
Application-specific Protocols 24
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Flow Control 26
Buffers 27
Event-driven Programming and Polling 28
Acknowledgments 29
Error Checking 29
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Device Manager 31
Port Resources 36
Serial Servers 37
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Drivers 38
Identifying Ports 39
GUIDs for COM Ports 39
COM Port Numbering 40
INF Files 40
Options for Application Programming 41
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