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`The
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`Protocols, Applications and Programming
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`Friedhelm “Schmidt
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`Transiatecl by
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`J. Michael Schultz
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`TransTech Translations
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`A V
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`ADDISON-WESLEY
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`Wokingham, England - Reading, Massachusetts - Menlo Park‘, California - New York
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`Don Mills, Ontario ° Amsterdam - Bonn - Sydney 0 Singapore
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`Tokyo 0 Madrid 0 San Juan 0 Milan 0 Paris 0 Mexico City: Seoul - Taipei
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`© 1995 Addison-Wesley Publishers Ltd.
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`‘© 1995 Addison-Wesley Publishing Company Inc,
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`Translated from the German edition SCSI-Bits und IDE-Schnittstelle
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`published by Addison-Wesley (Deutschland) GmbH.
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`TR 7gjf?s’
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`All rights reserved. No part of this publication may be reproduced, stored in a retrieval
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`system, or transmitted in any form or by any means, electronic, mechanical,
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`photocopying, recording or otherwise, without prior written permission of the
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`The programs in this book have been included for their instructional value. They have
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`been tested with care but are not guaranteed for any particular purpose. The publisher
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`does not offer any warranties or representations nor does it accept any liabilities with
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`Many of the designations used by manufacturers and sellers to distinguish their
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`products are claimed as trademarks. Addison-Wesley has made every attempt to
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`supply trademark information about manufacturers and their products mentioned in
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`Cover designed by Designers 8: Partners, Oxford
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`and printed by The Riverside Printing Co. (Reading) Ltd.
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`Typeset by VAP Group, Kidlington, Oxon.
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`Printed and bound in Great Britain at T.]. Press (Padstow) Ltd, Padstow, Cornwall
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`First printed 1995
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`ISBN 0-201-42284-0
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`British Library Cataloguing in Publication Data
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`A catalogue record for this book is available from the British Library.
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`94-23813
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`Library of Congress Cataloging-in-Publication Data
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`Schmidt. Friedhelm
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`(SCSI-Bus und IDE-Schnittstelle. English)
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`The SCSI bus and IDE interface/Friedhehn Schmidt; translated by
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`Michael Schultz.
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`p. cm.
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`Includes index.
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`ISBN 0-201-42284-0
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`1._S.CSI (Computer bus) 2. IDE (Standard)
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`TI<78_9_5.B87S36 1995
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`004-.6‘2--dc20
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`I. Title
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`Preface
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`The SCSI bus and IDE interface are without question the two most important
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`interfaces for computer peripherals in use today. The IDE hard disk interface is
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`found almost exclusively in the world of IBM PC Compatibles. The SCSI bus, on
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`the other hand, is designed not only for hard drives but also for tape drives, CD-
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`ROM, scanners, and printers. Almost all modern computers, from PCs to work-
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`stations to mainframes, are equipped with a SCSI interface.
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`Both SCSI and IDE are ANSI standards. However, aside from the actual
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`ANSI documentation, there exists almost no additional reference material to
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`either specification. The purpose of this book is to fill that void with a clear, con-
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`cise description of both interfaces. The essential terminology is introduced,
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`while the commands and protocols are broken down in full. In the interest of
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`economy the less important details and options have been omitted in certain
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`cases. Often a specific section in the ANSI documentation will be cited for easy _
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`cross-referencing. After reading this book you should be in the position to easily
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`understand relevant technical documentation, including the ANSI specifications
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`First and foremost, a thorough introduction to the terminology is in
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`order. Especially with respect to SCSI, there is a deluge of terms and definitions
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`that are used nowhere else or are used differently than in other computer
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`domains. These keywords, which include signal names and interface com-
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`mands, are typeset in small capital letters, for example FORMAT UNIT.
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`This book is intended for readers with a broad range of technical back-
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`grounds and interests. Those working on the design of mass storage devices, for
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`example, will find the protocol descriptions extremely useful. Readers writing soft-
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`ware or device drivers may have other interests. They will find the hardware
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`descriptions, such as that of the physical organization of a disk drive, very helpful.
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`This book is not meant to replace the ANSI documentation. On the other
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`hand, those specifications are not meant to explain the technology, rather to
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`define it. It is very difficult to find your way around in the original documenta-
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`tion without an understanding of the subject matter. The book's thorough, in-
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`depth descriptions, along with index and glossary, make it the perfect tutor for
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`IDE and SCSI, as well as a helpful guide to the ANSI literature.
`Friedhelm Schmidt
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`February 1993
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`HUAWEI EX. 1006 - 5/312
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`Contents
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`Preface
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`Introduction
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`Computers and peripherals
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`1.1 Mass storage
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`Peripheral interfaces
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`Traditional peripheral interfaces
`The RS-232 serial interface
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`2.2
`The Centronics printer interface
`2.3 Hard disks and their interfaces
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`Computer buses
`Characteristics of buses
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`3.2
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`Part II The IDE interface
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`Background
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`The origin of IDE
`4.2 Overview
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`4.3 ' Outlook
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`4.4 Documentation
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`The physical IDE interface
`The electrical interface
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`IDE protocol
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`6.1
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`6.2 Command execution
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`Contents
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`7 The model of an IDE disk drive
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`7.1 Organization of the medium
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`7.2 Defect management
`The sector buffer
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`IDE commands
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`8.1 Mandatory commands
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`The SCSI bus
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`Background
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`9.2 Overview
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`9.4 Documentation
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`SCSI hardware
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`10.1 SCSI configurations
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`10.2 SCSI signals
`10.3 Cables and connectors
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`10.4 Single-ended SCSI
`10.5 Differential SCSI
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`10.6 SCSI bus phases
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`10.7 Synchronous transfers and Fast SCSI
`10.8 Wide SCSI
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`SCSI bus protocol
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`11.1 The message system
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`11.3 SCSI pointers
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`11.4 Disconnect—reconnect: freeing the bus
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`11.5 Transfer options
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`11.6 Tagged queues
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`11.7 Termination of I/O processes
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`11.8 Error handling in the message system
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`11.9 Asynchronous event notification
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`SCSI commands
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`12.1 The SCSI target model
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`12.2 Command descriptor blocks
`12.3 Commands for all SCSI devices
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`12.4 Mode parameter pages for all device classes
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`SCSI Bus and IDE interface
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`13 Direct access devices
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`13.1 The model of a SCSI disk drive
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`13.2 Hard disk commands ’
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`13.3 Mode parameter pages for disk drives
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`Tape drives
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`14.1 The model of a SCSI tape drive
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`14.2 Commands for tape devices
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`14.3 Mode parameters for tape devices
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`Printers
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`15.1 The model of a SCSI printer
`15.2 Printer commands
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`15.3 Mode parameters for printers
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`Scanners
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`16.1 The model of a SCSI scanner
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`16.2 Scanner commands
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`16.3 Mode parameters for scanners
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`Processor devices
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`17.1 The model of a SCSI processor device
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`17.2 Commands for processor devices
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`Communications devices
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`18.1 The model of a SCSI communications device
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`18.2 Commands for SCSI communications devices
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`18.3 Mode parameter pages for communications devices
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`Optical storage and WORM drives
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`19.1 The SCSI model of optical storage
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`19.2 Commands for optical storage and WORM drives
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`19.3 Mode parameters for optical storage
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`CD~ROM
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`20.1 The model of a SCSI CD—ROM drive
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`20.2 Commands for CD—ROM
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`20.3 Audio commands for CD—ROM
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`20.4 Mode parameters for CD-ROMS
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`Medium-changer devices
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`21.1 The model of a SCSI medium-changer device
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`21.2 Commands for medium-changers
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`21.3 Mode parameter pages for medium-changers
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`The SCSI monitor program
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`Software interfaces
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`23.1 The concept of ASPI
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`23.2 SCSI request blocks
`23.3 ASPI initialization and function calls
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`Test equipment
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`24.1 SCSI analyzers
`24.2 SCSI emulators
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`24.3 Examples from industry
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`SCSI protocol chips
`25.1 The NCR 5385
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`25.2 Target applications: EMULEX ESP200
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`25.3 PC host adapters: FUTURE DOMAIN TMC-950
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`Appendix A
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`SCSI commands (by opcode)
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`Appendix B
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`SCSI commands (alphabetically)
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`Appendix C
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`SCSI sense codes
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`Appendix D
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`The SCSI bulletin board
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`Appendix E
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`Source code for SCANSCSLPAS
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`Glossary
`Index
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`HUAWEI EX. 1006 - 9/312
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`HUAWEI EX. 1006 - 10/312
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`HUAWEI EX. 1006 - 10/312
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`Part I
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`Introduction
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`1 Computers and peripherals
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`2 Traditional peripheral interfaces
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`3 Computer buses
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`HUAWEI EX. 1006 - 11/312
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`HUAWEI EX. 1006 - 12/312
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`1 Computers and peripherals
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`A computer can be broken down into a number of interdependent functional
`blocks. The most important of these are the central processing unit (CPU), main
`memory,
`input/ output (I/O) and mass storage. The CPU executes the
`instructions of a program, which, along with the necessary data, must reside in
`main memory at execution time. Therefore, before a program can be run it must
`be loaded into main memory from mass storage. The data to be processed by the
`program comes either from mass storage or from an input device such as the
`keyboard. The CPU accesses memory at least once for each program step in order
`to read the corresponding machine instructions. In fact, several accesses are
`usually necessary to read and write data. For this reason the CPU and memory
`are very tightly coupled: access is uncomplicated and, above all, fast.
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`Figure 1.1 Computer system with peripheral devices.
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`In contrast to memory, I/O devices and mass storage are located further
`from the CPU, hence the name ‘peripherals’ (Figure 1.1). Access to such devices
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`SCSI Bus and IDE Interface
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`is slower and more complicated. Communication with the peripherals is
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`accomplished using an interface such as SCSI or IDE. On the other end of the
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`interface is a controller, which in turn communicates with the CPU and memory.
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`Mass storage
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`A mass storage device is capable of storing data many times the size of main
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`memory. In addition, information stored here is nonvolatile: when the device is
`turned off the data remains intact.
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`Hard disks
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`Disk drives or hard disks store information by writing it onto rotating disks. The
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`information is divided up into blocks of fixed length, each of which can be
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`accessed relatively quickly, typically around 30 milliseconds (ms). For this
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`reason hard disks are also referred to as random access mass storage devices.
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`medium drives, diskettes, optical disks and CD-ROM.
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`In contrast to hard disks, tape devices (or tape drives) write data sequentially
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`onto magnetic tape. The length of time needed to access a specific block of
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`information depends on which position is presently underneath the read /write
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`head. If it is necessary to rewind or fast forward the tape a very long distance, a
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`tape access can take as long as several minutes. Tape drives are also known as
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`sequential mass storage devices. Among these are the traditional reel-to-reel
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`drives, cassette drives, drives that use video cassettes for recording and 4mm
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`digital audio tape (DAT) drives.
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`Under the heading 1/0 devices are the monitor and keyboard used for
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`communication between the user and the computer. Further examples of output
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`devices are printers, plotters and even speakers used for outputting speech.
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`Among the many input devices are mice, analog to digital converters, scanners
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`Network connections also fall into this category. This is especially so
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`today where mass storage is often replaced by a file server across a network.
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`Computers with no mass storage of their own are called diskless workstations.
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`There are many more devices that exchange data with computers, although one
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`hardly refers to a computer controlied lathe or a music synthesizer as a
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`computer peripheral. Nevertheless,
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`communicate with the computer using 1/0.
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`Miscellaneous
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`HUAWEI EX. 1006 - 14/312
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`1.2 Peripheral interfaces
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`Computers and peripherals
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`Peripheral devices are connected to computer systems via interfaces. The
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`abstract model of a peripheral interface is made up of many layers,
`the
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`boundaries of which are not always clear, especially for older interfaces. It is also
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`true that some layers are omitted in certain interface definitions. In this book I
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`adhere to a model with four layers for the SCSI interface, as was agreed upon by
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`the American National Standards Institute (ANSI) committee for the first time
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`for SCSI—3. The strata of layers are designed bottom up. All low level layers are
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`mandatory for the implementation of an interface. An uppermost layer,
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`however, can be omitted in some cases. A high level interface refers to the case
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`where all possible levels have been implemented.
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`Among those things defined in the lowest level are cable and connector
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`types. Also defined are the signal voltages and the current requirements of the
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`drivers. Finally, the timing and coordination of all of the signals of the bus are
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`described here. This lowest level is referred to as the physical interface.
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`Directly above the physical layer resides the protocol layer. The protocol
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`of an interface contains, for example, information about the difference between
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`data bytes and command bytes and about the exchange of messages between
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`devices. If corrupted data is to be corrected through the use of error correction,
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`this is described in the interface protocol.
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`On top of the protocol layer lies the peripheral device model. Here the
`behavior of devices to be connected to the interface is described. These
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`descriptions can be very detailed and precise. The SCSI bus is an example of.
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`such a detailed model, where in addition to the characteristics of general
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`purpose SCSI devices, those of hard disks, tape drives, printers and so on are
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`defined.
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`Finally, some interfaces go so far as to define which commands must be
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`understood by the interface devices. The command set builds upon the device
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`model and represents the fourth layer of the interface.
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`The term ‘interface’ always refers to all implemented layers in their
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`entirety. There are distinct peripheral interfaces defined using the same physical
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`level but a unique protocol level. It is also possible for a single interface to allow
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`for different options in the physical level.
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`The interface used for printers is a good example of a four-layer
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`interface. Figure 1.2 makes the relationships among the layers clear. The two
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`lower levels are covered by the Centronics interface. This parallel interface
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`contains the definition of the physical and protocol layers. The particular printer
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`model in Figure 1.2 is a page printer. This means that the printer constructs an
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`entire page in internal memory before printing it. In contrast to line printers, the
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`lines of a page can be sent in any order as long as a page boundary is not crossed.
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`However, once a page is printed it is impossible to retrieve it in order to make
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`The page description language PostScript is an excellent example of a
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`large and complex command set. It is built upon the page printer model and
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`makes it possible to output text as well as various graphic elements. These
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`elements can be positioned freely on the current page. Naturally, there are other
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`HUAWEI EX. 1006 - 15/312
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`Command set
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`Postscript
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`Device model
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`printer
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`........CemrQn|'c5 ....... ..
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`Protocol
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`Physical
`interface
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`SCSI Bus and IDE Interface
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`Figure 1.2 Layers of a printer interface.
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`such page formatting languages written for the page printer model. This makes
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`the division between device and language very intuitive.
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`As you can see, this interface is complete in that it contains all four
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`interface layers. If you purchase a printer with such an interface, it makes no.
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`difference which brand name you choose. As long as it is true to the interface
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`specification it will Work with any computer also equipped with ‘the printer
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`interface. However, if you were to omit even only the uppermost layer of the
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`specification, then the interface description would be incomplete. It would still
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`be possible to connect up the printer, but whether it would function properly
`would be a matter of luck.
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`The IDE interface and the SCSI bus are likewise" complete interface
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`definitions. Before getting to these, however, I would like“ to introduce in
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`Chapter 2 a few classic examples of peripheral interfaces. For the most part their
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`definitions contain only the lower layers of the interface model. This chapter will
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`help to underscore the difference between traditional interfaces on the one hand
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`and the complete IDE and SCSI interfaces on the other.
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`HUAWEI EX. 1006 - 16/312
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`2 Traditional peripheral
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`interfaces
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`This chapter will help to familiarize you with several classic peripheral inter-
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`faces of the computer industry. As with the printer interface outlined in Chapter
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`1, these will be described within the framework of the layered interface model.
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`These descriptions are by no means comprehensive; complete specifications
`would turn this book into several volumes.
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`I have two goals in mind in presenting these interfaces. First of all, the
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`interfaces are very simple; they will allow you to become acquainted with inter-
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`face characteristics that are valid for all interfaces, including computer buses.
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`Secondly, to a certain degree these specifications are the forerunners of competi-
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`tion to the IDE and SCSI bus interfaces. A background in the more traditional
`interfaces will make it much easier to evaluate and understand their modern
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`descendants, the main topic of this book.
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`The RS-232 serial interface
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`RS-232C is the most widely used serial interface. ‘Serial’ means that the data is
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`transferred one bit at a time across a single connection. RS-232C is used mainly
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`for the connection of computer terminals and printers. Nonetheless, it is also
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`appropriate for the exchange of data between computers. Machine tools and
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`measurement instruments are frequently connected to computers using RS-
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`232C. Understandably, it is not a device specific interface. RS-232C is the respon-
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`sibility of the Electronic Industries Association (EIA).
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`The specification for RS-232C contains the physical layer and hardware
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`protocol. In addition, there are software protocols, of which only a few build on
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`top of the RS-232 hardware protocol. This leads to an uncommon situation with
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`RS-232C and other serial interfaces — not all applications use all of the signals.
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`Frequently cables are used that conduct only a few of the defined signals, a sit-
`uation thatwould be unthinkable for IDE or SCSI. I concentrate here on a varia-
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`tion of the interface using only three signals, which I call mini-RS-232.
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`SCSI Bus and IDE interface
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`Mini-RS-232 establishes a bidirectional point~to~point connection between
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`equipment. Each direction has its own data signal and a single ground signal is
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`shared. The data signals are called TD (transmit data) and RD (receive data).
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`When two devices are coupled to each other, these signals are crossed such that
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`the TD of .one device connects to the RD of the other (Figure 2.1).
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`The physical
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`Step bit
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`(always 1)
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`Signal ground
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`Transmit dala TransmIt dale
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`Fleoelve data
`Receive data
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`25
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`Figure 2.1 Physical interface: mini-RS-232.
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`The connector chosen by the EIA standard is the 25-pin DB25. Other con-
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`nectors, however, are frequently employed, such as the DB9 for the IBM AT or
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`the R111 telephone connector used in various minicomputers.
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`On the signal lines, a logical 1 is represented by a voltage between +5 V
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`and +15 V, and the receiver recognizes anything above +3 V as such. Likewise,
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`logical O is represented by a signal voltage between -5 V and -15 V. Again, the
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`receiver recognizes any signal below -3 V as such.
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`Data transfer takes place serially, character by character. The characters
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`are further broken down into bits, which are sent across the line one by one. On
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`the other end, the receiver then assembles the bits back into characters. The
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`number of bits per character lies between five and eight; eight is precisely what
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`is needed to transfer one byte. The data bits are preceded by a start bit and fol-
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`lowed by a stop bit. In addition, a parity bit may be sent for error detection. The
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`transfer rate-can range between '75 and 115 000 bits per second (baud), and a
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`cable alone cannot compensate for different transfer rates; the devices must be
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`set at the same speed otherwise no exchange of data can take place.
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`Now comes a rather confusing point: this method of transfer over the
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`serial interface is called asynchronous even though the data is sent and received
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`relative to a clock. Among other serial interfaces the term ’synchronous’ is used
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`whenever a clock is involved. For RS-232C, however, the transfer is referred to
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`as asynchronous because the clocks are not tied to each other. The RS-232C spec-
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`ification includes signals that allow the sender and the receiver to use the same
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`clock for data transfer. When these signals are employed the data transfer is
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`Traditional peripheral interfaces
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`referred to as synchronous. True asynchronous transfer uses control signals to
`exchange data. This point, among others, will be made clear in Section 2.2.
`As a rule of thumb, when thinking about data throughput you can con-
`sider a byte or character to be 10 bits (one stop, one start and eight data bits).
`When the fastest transfer rate possible is employed, namely 115 000 bits per sec-
`ond, the maximum throughput is approximately 11.5 Kbytes per second.
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`The protocol Mini-RS-232 has no protocol of its own. However, there is a protocol that is often
`used with the interface, called the XON/XOFF protocol (Figure 2.2). It works in
`the following way. When the receiving device is no longer able to take on data
`from the sender, it sends a special character, an XOFF byte, to indicate this. Later,
`when it is ready to continue receiving data, it sends an XON byte to tell the
`sender to proceed. This protocol is in no way error proof — characters are some-
`times lost. In addition, the protocol cannot be used for bidirectional transfer of
`binary data. The reason for this restriction is simple: for text data only a subset
`of the possible bytes is sent over the interface, those corresponding to letters,
`numbers, and symbols. This leaves room for a number of special characters, of
`which XON and XOFF are examples. When, on the other hand, binary data is
`transferred, the data is not restricted to certain characters; any binary pattern
`may occur. In this situation there is no room for the special characters and the
`XON/XOFF protocol is unusable. For connecting monitors and printers, how-
`ever, the protocol is actually very practical.
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`IIIIHIIIEIHI
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`HHIIIII
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`Printer
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`XOFF
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`XON
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`Figure 2.2 XON/XOFF protocol.
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`An example of a higher level protocol for the transfer of binary data (file
`transfer) is Kermit. This public domain program can be used at no cost for non-
`commercial purposes. A number of computer manufacturers have also devel-
`oped their own internal protocols built on top of RS-232
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`There are no commands special to the RS-232 interface. As RS-Z32 was devel-
`oped, commands were designed for specific devices apart from the interface.
`SCSI is among the first interfaces to define universal command sets for whole
`device classes.
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`Nevertheless, some command sets have been designed for use with RS-
`232. Examples are page formatting languages for printers, such as Postscript.
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`SCSI Bus and IDE Interface
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`Summary As you can see, an interface that builds on top of RS-232 has many possible vari-
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`ations. The complete description of-my printer—PC interface would be: RS-232 at
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`9600 baud, 1 stop bit, no parity, XON/XOFF protocol, PostScript. If I were to
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`change a parameter for only the printer or only the PC, for example by not send-
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`ing PostScript or starting to use a parity bit, nothing would print. Although
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`mini-RS-232 appears to be simple (only three wires), there are almost an
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`uncountable number of ways in which the connection can fail. What is missing
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`is a protocol that allows the devices to agree upon the available options.
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`Although RS-232 has given a good portion of frustration to just about everyone
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`who has worked with it, it nonetheless has the decided advantage that it exists
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`on every computer and is also device independent.
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`The Centronics printer interface
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`The Centronics interface is a parallel interface developed for printers. It is an
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`industry standard that, to my knowledge, has never been officially approved. As
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`a result there are many variations. This is especially so with respect to the status
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`signals that reflect the printer's current state. Centronics defines the physical
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`interface and the protocol. As a command set, either PostScript or another print-
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`er language is used.
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`Originally developed as a Lmidirectional interface, the parallel printer
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`"link for PCs can also be used bidirectionally. This extension is not our concern
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`here. We are interested in Centronics mostly as another example of the various
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`computer interfaces. However, it is also a good idea to know this interface in
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`order to understand the difference from SCSI printers (see Figure 2.3).
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`Centronics uses a shielded twisted-pair cable with 36 signals, of maximum
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`length 5 meters (about 16 feet). A 36-pin amphenol connector is used on the
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`printer end, which most peopl