SMALL COMPUTER SYSTEM INTERFACE (SCSI)
BSR X3.131-198_
NOTE: Revision 17B consists of changes made by the X3T9/84-40 REV 1B
X3T9.2 task group at their December 10, 1985 meeting. X3T9.2/82-2
These changes were made in order to make the X3T9.2 REV 17B
draft proposed standard consistent with the ISO/TC97/SC13
draft proposal. See page 1.1 for a changed page list.
draft proposed
American National Standard
for information systems -
SMALL COMPUTER SYSTEM INTERFACE (SCSI)
December 16, 1985
Secretariat
Computer and Business Equipment Manufacturers Association
Abstract: This standard defines mechanical, electrical, and functional
requirements for attaching small computers with each other and with low- to
medium-performance intelligent peripherals such as rigid disks, flexible
disks, magnetic tape devices, printers, and optical disks. The resulting
interface facilitates the interconnection of small computers and intelligent
peripherals and thus provides a common interface specification for both
systems integrators and suppliers of intelligent peripherals.
POINTS OF CONTACT:
William E. Burr (X3T9.2 Chairman) John B. Lohmeyer (X3T9.2 Vice Chairman)
U.S. Department of Commerce NCR Corporation
National Bureau of Standards 3718 N. Rock Road
Technology A-216 Wichita, KS 67226
Gaithersburg, MD 20899 (316) 688-8703
(301) 921-3723
CHANGED PAGE LIST
At their December 10, 1985 meeting, the X3T9.2 task group made a number of
changes to Revision 17 of this document. (Revision 17A was distributed at the
meeting proposing some of the changes; the remainder of the changes were made
at the meeting.) The primary reason for making these changes is to keep this
document consistent with the ISO/TC97/SC13 SCSI draft proposal. The pages
that have changed since Revision 17 are listed below:
Page Change
------- -------------------------------------------------------------------
1 Changed revision number and date.
1.1 Replaced changed page list.
2 Editorial revisions to the foreword.
7-7.1 Revised the Table of Contents to reflect the document changes.
9 Added description of the contents of appendixes D - G.
12 Moved section 4.3.2, Shielded Connectors into Appendix D. Merged
section 4.3.1 into section 4.3.
12.1-12.2 \
17-19 \ Deleted pages
19.1-19.4 / (Information moved to Appendix D).
21.1-21.2 /
20-21 Deleted second line of Table titles.
24 Redrew figures 4-5 through 4-7.
26 Redrew figure 4-9.
37 Clarified that multiple messages may be sent during a message phase.
38 Clarification to the MESSAGE OUT phase error handling.
41 Redrew figures 5-1 and 5-2.
43 Editorial clarification.
49 Deleted "immediately".
50-50.1 Clarified that unit attention condition is on a per logical unit
basis. Also clarified "other" command is other than REQUEST SENSE.
65-66 Added ISO version field to the INQUIRY data.
93.1 Revised Table 8-14.1 to reference the latest X3B5 document number
and to refer to Appendix F for additional standards.
94-99 Editorial clarifications to the RESERVE and RELEASE commands.
113 Clarified which status codes are to be returned on SEARCH DATA
commands.
119 Clarified that READ BLOCK LIMITS returns the target's capability as
opposed to its current setting.
132 Added code values 0BH through 0DH to Table 9-14.1.
132.2-133 Editorial clarifications to the RESERVE UNIT and RELEASE UNIT
commands.
147-149 Editorial clarifications to the RESERVE UNIT and RELEASE UNIT
commands.
174-176.2 Revised Appendix A to make the figure legible.
182-183 Redrew figures C1 and C2.
184-192 Added Appendix D, Recommended Shielded Connectors. Most of this
information was previously in section 4.3.2.
193-194 Added Appendix E, Conformance.
195-196 Added Appendix F, Additional Medium Type and Density Code Standards.
197 Appendix G was previously Appendix D. Editorial clarification.
FOREWORD
(This Foreword is not part of American National Standard X3.131-198_.)
The development of comparatively inexpensive VLSI device controllers have
recently changed the economics of interfaces for small system storage devices.
Where expensive controller logic was once shared among as many devices as
possible, in many cases it now makes economic sense to build a controller in
each device. This is particularly true for high-performance storage devices,
where the intimate interactions of the recording medium, the recording
mechanism, and the recording code cause intersymbol interference and error
recovery problems that are highly specific to the chosen technologies, and are
best resolved within the device itself.
Moreover, the number of types of storage devices for small computers, and the
industry that builds them, have grown dramatically in the past few years. In
particular, the emergence of physically small, but comparatively high-capacity
and high-performance fixed-medium magnetic disk devices (virtually non-
existent in the late 1970s, but a multibillion dollar business in the mid-
1980s) has driven the development of small computer systems and caused a need
for other classes of devices, such as streaming cartridge tape drives, for
backup and data interchange.
Because device interfaces are very specific to device types, many device level
interface standards would be required to service all small computer device
types. Because backplane buses reside at the center of computers, and have
dramatic performance effects, many different ones are needed for different
system requirements. To connect every backplane bus to every device interface
through a controller would require an almost unbounded number of specific
controller products.
In addition, in many systems today, it is not the computer which is "central",
it is the storage facility. That is, one or two large capacity storage
subsystems serve several computers. An interface adapted to this reality was
needed.
By 1982, all the needs given above were widely recognized in the industry and
by the members of X3T9 and its Task Groups. A commercial small system
parallel bus, the Shugart Associates System Interface (SASI), generally met
the small system requirements for a device-independent peripheral or system
bus and had enjoyed significant market success. It was offered to X3T9.2 as
the basis for a standard. X3T9.2 chose the name Small Computer System
Interface (SCSI) for that standard and began work at its April 1982 meeting.
The present SCSI dpANS is a formalization and extension of the SASI. Many
existing SASI devices are SCSI compatible.
Since April 1982, X3T9.2 has held plenary sessions, at two month intervals,
plus numerous informal working meetings. The original SASI has been extended
in a number of ways, including:
(1) A differential electrical option has been added to allow use of longer
cables (up to 25 meters) in environments where common mode noise is a concern.
(2) A synchronous transfer option has been developed allowing maximum
transfer rates in the 3 to 4 megabyte per second range.
(3) An optional "extended" command set has been added, allowing for very
large capacity storage devices (a block address space of 232 blocks versus 221
for SASI), and Inquiry commands that allow self-configuring driver software.
(4) Command sets for magnetic tape (both start/stop and streaming),
printers, processors, optical disks, and read-only optical disks have been
added to the proposed SCSI standard, in addition to those for magnetic disks.
Although it might have been premature in April 1982 to claim that SASI was
then a de facto standard, this surely is the case for SASI/SCSI today. SCSI
compatible host adapters, controllers, and peripheral devices are now widely
manufactured around the world. Host adapters are available for most small
computers with accessible backplane buses. SCSI controllers are widely
available for all the de jure and de facto standard magnetic disk and magnetic
tape device interfaces. Small high-capacity fixed-medium magnetic disks,
rigid removable-medium magnetic disks, high-capacity Bernoulli-effect flexible
disks, and other closed-loop high-capacity flexible disk products, as well as
optical disk products, are all available with integral SCSI controllers. SCSI
subsystems that integrate both a rigid-disk and a streaming-tape drive into a
single package are also available. SCSI interface chips are available, and
some disk controller chip sets also provide SCSI support.
Since a large number of companies have implemented and tested the SCSI during
the development of the proposed standard, no separate test program has been
deemed necessary. At the February 1984 meeting of X3T9.2, representatives of
the following companies stated, for the record, that their companies had
implemented and tested SCSI: Adaptec, Adaptive Data, Data Technology Corp.,
Fujitsu America, Inc., NCR Corp., and Shugart Corp. This is not a complete
list of companies implementing products using SCSI nor is it a promise by
these companies to offer SCSI products.
The SCSI fills an urgent need, provides for the future, and is consonant with
actual commercial practice. Most important, the timing is right. SCSI
catches the floodtide of new, high-performance storage devices for small
systems, and promises to bring a measure of needed order to what would
otherwise be a chaotic and fragmented market.
This standard specifies the mechanical, electrical, and functional
requirements for a small computer input/output bus interface, and command sets
for peripheral device types, particularly storage devices, commonly used with
small computers.
Suggestions for improvement of this standard will be welcome. They should be
sent to the Computer and Business Equipment Manufacturers Association, 311
First Street, NW, Suite 500, Washington, DC 20001.
This standard was processed and approved for submittal to ANSI by American
National Standards Committee on Computers and Information Processing, X3.
Committee approval of the standard does not imply that all committee members
voted for its approval.
At the time it approved this standard, the X3 Committee had the following
members:
TO BE DETERMINED
Subcommittee X3T9 on I/O interfaces, which reviewed this standard, had the
following members:
Delbert L. Shoemaker (Chairman)
Ron Tranquilli (Vice Chairman)
Bob Bender G. Atterbury (Alt)
John Blagaila Charles Brill (Alt)
Fred Ciechowski William E. Burr (Alt)
George Clark Roger Cormier (Alt)
Stephen W. Cooper Hank Dorris (Alt)
Louis C. Domshy Thomas A. Fiers (Alt)
Robert Dugan Henry Ginter (Alt)
Ross H. Jaibaji William J. McClain (Alt)
Patrick Lannan William Mosenthal, Jr. (Alt)
Gene Milligan Kirk Moulton (Alt)
Tom Morrow
Mike Newton
Gary S. Robinson
Arnold John Roccati
Floyd E. Ross
Holly S. White
(Note: The name lists on this page and the following page are incomplete and
they will be updated upon final approval of this standard.)
Task Group X3T9.2 on Lower-Level Interfaces, which developed this standard,
had the following members:
William E. Burr (Chairman)
John B. Lohmeyer (Vice Chairman)
Ezra R. Alcudia Keith Amundsen (Alt)
J. L. Amstutz Karen Anneberg (Alt)
Bob Bender Charles Brill (Alt)
John Blagaila Larry Boucher (Alt)
Tom Briggs Paul Clement (Alt)
David T. Cornaby George E. Clark (Alt)
David F. Craft, Jr. Steve Cooper (Alt)
Jay Cunningham Gary Crowell (Alt)
Willard S. Davidson Jon Ericson (Alt)
Terry Dawson Tom Fiers (Alt)
Phil Devin Stephen Fitzgerald (Alt)
Louis C. Domshy Marty Francis (Alt)
Norm Dornseif William Homans (Alt)
Alan Ebright J. V. Howell (Alt)
Anita Freeman Skip Kilsdonk (Alt)
Abe Gindi Jim Korpi (Alt)
William A. Horton Lawrence J. Lamers (Alt)
Frank Krulc Keith Mueller (Alt)
Patrick E. Lannan Don Nanneman (Alt)
Daniel Loski Doug Nolff (Alt)
William C. Mavity Richard Reiser (Alt)
Gene Milligan William H. Roberts (Alt)
Bob Mortensen Floyd E. Ross (Alt)
Gary S. Robinson D. Michael Robinson (Alt)
Don Rodgers Jay Seashore (Alt)
Arnold J. Roccati Chuck Spatafore (Alt)
Jack Schiffhauer Jeff Stai (Alt)
Ralph H. Schultz Paul Stavish (Alt)
Moshe Segal
Delbert L. Shoemaker
Tim Slaton
Robert N. Snively
Adrienne Turenne
Norm Zimmerman
T A B L E O F C O N T E N T S
1. Scope...................................................................8
2. Referenced Standard.....................................................9
3. Glossary and Conventions................................................9
3.1 Glossary...........................................................9
3.2 Editorial Conventions.............................................11
4. Physical Characteristics...............................................11
4.1 Physical Description..............................................11
4.2 Cable Requirements................................................11
4.3 Connector Requirements............................................12
4.4 Electrical Description............................................22
4.5 SCSI Bus..........................................................25
4.6 SCSI Bus Signals..................................................27
4.7 SCSI Bus Timing...................................................30
5. Logical Characteristics................................................31
5.1 SCSI Bus Phases...................................................31
5.2 SCSI Bus Conditions...............................................38
5.3 SCSI Bus Phase Sequences..........................................40
5.4 SCSI Pointers.....................................................42
5.5 Message System Specification......................................42
6. SCSI Commands .........................................................49
6.1 Command Implementation Requirements...............................50
6.2 Command Descriptor Block........................................50.1
6.3 Command Examples..................................................55
7. Command Descriptions for All Device Types..............................57
7.1 Group 0 Commands for All Device Types.............................57
7.2 Group 1 Commands for All Device Types.............................76
7.3 Group 2 Commands for All Device Types.............................79
7.4 Group 3 Commands for All Device Types.............................79
7.5 Group 4 Commands for All Device Types.............................79
7.6 Group 5 Commands for All Device Types.............................79
7.7 Group 6 Commands for All Device Types.............................79
7.8 Group 7 Commands for All Device Types.............................79
8. Command Descriptions for Direct-Access Devices.........................80
8.1 Group 0 Commands for Direct-Access Devices........................80
8.2 Group 1 Commands for Direct-Access Devices.......................104
9. Group 0 Command Descriptions for Sequential-Access Devices............117
10. Group 0 Command Descriptions for Printer Devices......................140
11. Group 0 Command Descriptions for Processor Devices....................152
12. Command Descriptions for Write-Once Read-Multiple Devices.............155
12.1 Group 0 Commands for Write-Once Read-Multiple Devices...........155
12.2 Group 1 Commands for Write-Once Read-Multiple Devices...........164
13. Command Descriptions for Read-Only Direct-Access Devices..............170
13.1 Group 0 Commands for Read-Only Direct-Access Devices............170
13.2 Group 1 Commands for Read-Only Direct-Access Devices............171
14. Status ...............................................................172
L I S T O F F I G U R E S
4-1 Nonshielded SCSI Device Connector.....................................13
4-2 Nonshielded Cable Connector...........................................15
4-5 Termination for Single-Ended Devices..................................24
4-6 Termination for Differential Devices..................................24
4-7 Differential Driver Protection Circuit (Optional).....................24
4-8 SCSI ID Bits..........................................................25
4-9 Sample SCSI Configurations............................................26
5-1 Phase Sequences without Arbitration...................................41
5-2 Phase Sequences with Arbitration......................................41
5-3 Simplified SCSI System................................................42
Appendixes
Appendix A................................................................174
SCSI Signal Sequence Example
Appendix A Figures
A1: SCSI Timing Chart ...............................................175
Appendix B................................................................177
Typical Bus Phase Sequence
Appendix C................................................................179
SCSI System Operation
C1. Host Memory / Host Adapter / SCSI Controller Relationship........179
C2. SCSI READ Command Example........................................180
C3. I/O Channel Concept..............................................181
Appendix C Figures
C1: Snapshot Prior to Initial Selection..............................182
C2: Snapshot Prior to Data Transfer..................................183
Appendix D................................................................184
Recommended Shielded Connectors
D1. Shielded Connector, Alternative 1................................184
D2. Shielded Connector, Alternative 2................................184
D3. EUROCARD Boxes...................................................184
Appendix D Figures
D1: Female Shielded SCSI Cable Connector, Alternative 1..............185
D2: Male Shielded SCSI Device Connector, Alternative 1...............187
D3: Shielded SCSI Device Connector, Alternative 2....................189
D4: Shielded SCSI Cable Connector, Alternative 2.....................190
Appendix E................................................................193
Conformance
E1. Alternatives.....................................................193
E2. Levels of Conformance............................................193
E3. Options..........................................................194
E4. Statement of Conformance.........................................194
Appendix F................................................................195
Additional Medium Type and Density Code Standards
Appendix G................................................................197
Future Standardization
NOTE: Revision 17B consists of changes made by the X3T9/84-40 REV 1B
X3T9.2 task group at their December 10, 1985 meeting. X3T9.2/82-2
These changes were made in order to make the X3T9.2 REV 17B
draft proposed standard consistent with the ISO/TC97/SC13
draft proposal. See page 1.1 for a changed page list.
draft proposed
American National Standard
for information systems -
SMALL COMPUTER SYSTEM INTERFACE (SCSI)
December 16, 1985
Secretariat
Computer and Business Equipment Manufacturers Association
Abstract: This standard defines mechanical, electrical, and functional
requirements for attaching small computers with each other and with low- to
medium-performance intelligent peripherals such as rigid disks, flexible
disks, magnetic tape devices, printers, and optical disks. The resulting
interface facilitates the interconnection of small computers and intelligent
peripherals and thus provides a common interface specification for both
systems integrators and suppliers of intelligent peripherals.
POINTS OF CONTACT:
William E. Burr (X3T9.2 Chairman) John B. Lohmeyer (X3T9.2 Vice Chairman)
U.S. Department of Commerce NCR Corporation
National Bureau of Standards 3718 N. Rock Road
Technology A-216 Wichita, KS 67226
Gaithersburg, MD 20899 (316) 688-8703
(301) 921-3723
CHANGED PAGE LIST
At their December 10, 1985 meeting, the X3T9.2 task group made a number of
changes to Revision 17 of this document. (Revision 17A was distributed at the
meeting proposing some of the changes; the remainder of the changes were made
at the meeting.) The primary reason for making these changes is to keep this
document consistent with the ISO/TC97/SC13 SCSI draft proposal. The pages
that have changed since Revision 17 are listed below:
Page Change
------- -------------------------------------------------------------------
1 Changed revision number and date.
1.1 Replaced changed page list.
2 Editorial revisions to the foreword.
7-7.1 Revised the Table of Contents to reflect the document changes.
9 Added description of the contents of appendixes D - G.
12 Moved section 4.3.2, Shielded Connectors into Appendix D. Merged
section 4.3.1 into section 4.3.
12.1-12.2 \
17-19 \ Deleted pages
19.1-19.4 / (Information moved to Appendix D).
21.1-21.2 /
20-21 Deleted second line of Table titles.
24 Redrew figures 4-5 through 4-7.
26 Redrew figure 4-9.
37 Clarified that multiple messages may be sent during a message phase.
38 Clarification to the MESSAGE OUT phase error handling.
41 Redrew figures 5-1 and 5-2.
43 Editorial clarification.
49 Deleted "immediately".
50-50.1 Clarified that unit attention condition is on a per logical unit
basis. Also clarified "other" command is other than REQUEST SENSE.
65-66 Added ISO version field to the INQUIRY data.
93.1 Revised Table 8-14.1 to reference the latest X3B5 document number
and to refer to Appendix F for additional standards.
94-99 Editorial clarifications to the RESERVE and RELEASE commands.
113 Clarified which status codes are to be returned on SEARCH DATA
commands.
119 Clarified that READ BLOCK LIMITS returns the target's capability as
opposed to its current setting.
132 Added code values 0BH through 0DH to Table 9-14.1.
132.2-133 Editorial clarifications to the RESERVE UNIT and RELEASE UNIT
commands.
147-149 Editorial clarifications to the RESERVE UNIT and RELEASE UNIT
commands.
174-176.2 Revised Appendix A to make the figure legible.
182-183 Redrew figures C1 and C2.
184-192 Added Appendix D, Recommended Shielded Connectors. Most of this
information was previously in section 4.3.2.
193-194 Added Appendix E, Conformance.
195-196 Added Appendix F, Additional Medium Type and Density Code Standards.
197 Appendix G was previously Appendix D. Editorial clarification.
FOREWORD
(This Foreword is not part of American National Standard X3.131-198_.)
The development of comparatively inexpensive VLSI device controllers have
recently changed the economics of interfaces for small system storage devices.
Where expensive controller logic was once shared among as many devices as
possible, in many cases it now makes economic sense to build a controller in
each device. This is particularly true for high-performance storage devices,
where the intimate interactions of the recording medium, the recording
mechanism, and the recording code cause intersymbol interference and error
recovery problems that are highly specific to the chosen technologies, and are
best resolved within the device itself.
Moreover, the number of types of storage devices for small computers, and the
industry that builds them, have grown dramatically in the past few years. In
particular, the emergence of physically small, but comparatively high-capacity
and high-performance fixed-medium magnetic disk devices (virtually non-
existent in the late 1970s, but a multibillion dollar business in the mid-
1980s) has driven the development of small computer systems and caused a need
for other classes of devices, such as streaming cartridge tape drives, for
backup and data interchange.
Because device interfaces are very specific to device types, many device level
interface standards would be required to service all small computer device
types. Because backplane buses reside at the center of computers, and have
dramatic performance effects, many different ones are needed for different
system requirements. To connect every backplane bus to every device interface
through a controller would require an almost unbounded number of specific
controller products.
In addition, in many systems today, it is not the computer which is "central",
it is the storage facility. That is, one or two large capacity storage
subsystems serve several computers. An interface adapted to this reality was
needed.
By 1982, all the needs given above were widely recognized in the industry and
by the members of X3T9 and its Task Groups. A commercial small system
parallel bus, the Shugart Associates System Interface (SASI), generally met
the small system requirements for a device-independent peripheral or system
bus and had enjoyed significant market success. It was offered to X3T9.2 as
the basis for a standard. X3T9.2 chose the name Small Computer System
Interface (SCSI) for that standard and began work at its April 1982 meeting.
The present SCSI dpANS is a formalization and extension of the SASI. Many
existing SASI devices are SCSI compatible.
Since April 1982, X3T9.2 has held plenary sessions, at two month intervals,
plus numerous informal working meetings. The original SASI has been extended
in a number of ways, including:
(1) A differential electrical option has been added to allow use of longer
cables (up to 25 meters) in environments where common mode noise is a concern.
(2) A synchronous transfer option has been developed allowing maximum
transfer rates in the 3 to 4 megabyte per second range.
(3) An optional "extended" command set has been added, allowing for very
large capacity storage devices (a block address space of 232 blocks versus 221
for SASI), and Inquiry commands that allow self-configuring driver software.
(4) Command sets for magnetic tape (both start/stop and streaming),
printers, processors, optical disks, and read-only optical disks have been
added to the proposed SCSI standard, in addition to those for magnetic disks.
Although it might have been premature in April 1982 to claim that SASI was
then a de facto standard, this surely is the case for SASI/SCSI today. SCSI
compatible host adapters, controllers, and peripheral devices are now widely
manufactured around the world. Host adapters are available for most small
computers with accessible backplane buses. SCSI controllers are widely
available for all the de jure and de facto standard magnetic disk and magnetic
tape device interfaces. Small high-capacity fixed-medium magnetic disks,
rigid removable-medium magnetic disks, high-capacity Bernoulli-effect flexible
disks, and other closed-loop high-capacity flexible disk products, as well as
optical disk products, are all available with integral SCSI controllers. SCSI
subsystems that integrate both a rigid-disk and a streaming-tape drive into a
single package are also available. SCSI interface chips are available, and
some disk controller chip sets also provide SCSI support.
Since a large number of companies have implemented and tested the SCSI during
the development of the proposed standard, no separate test program has been
deemed necessary. At the February 1984 meeting of X3T9.2, representatives of
the following companies stated, for the record, that their companies had
implemented and tested SCSI: Adaptec, Adaptive Data, Data Technology Corp.,
Fujitsu America, Inc., NCR Corp., and Shugart Corp. This is not a complete
list of companies implementing products using SCSI nor is it a promise by
these companies to offer SCSI products.
The SCSI fills an urgent need, provides for the future, and is consonant with
actual commercial practice. Most important, the timing is right. SCSI
catches the floodtide of new, high-performance storage devices for small
systems, and promises to bring a measure of needed order to what would
otherwise be a chaotic and fragmented market.
This standard specifies the mechanical, electrical, and functional
requirements for a small computer input/output bus interface, and command sets
for peripheral device types, particularly storage devices, commonly used with
small computers.
Suggestions for improvement of this standard will be welcome. They should be
sent to the Computer and Business Equipment Manufacturers Association, 311
First Street, NW, Suite 500, Washington, DC 20001.
This standard was processed and approved for submittal to ANSI by American
National Standards Committee on Computers and Information Processing, X3.
Committee approval of the standard does not imply that all committee members
voted for its approval.
At the time it approved this standard, the X3 Committee had the following
members:
TO BE DETERMINED
Subcommittee X3T9 on I/O interfaces, which reviewed this standard, had the
following members:
Delbert L. Shoemaker (Chairman)
Ron Tranquilli (Vice Chairman)
Bob Bender G. Atterbury (Alt)
John Blagaila Charles Brill (Alt)
Fred Ciechowski William E. Burr (Alt)
George Clark Roger Cormier (Alt)
Stephen W. Cooper Hank Dorris (Alt)
Louis C. Domshy Thomas A. Fiers (Alt)
Robert Dugan Henry Ginter (Alt)
Ross H. Jaibaji William J. McClain (Alt)
Patrick Lannan William Mosenthal, Jr. (Alt)
Gene Milligan Kirk Moulton (Alt)
Tom Morrow
Mike Newton
Gary S. Robinson
Arnold John Roccati
Floyd E. Ross
Holly S. White
(Note: The name lists on this page and the following page are incomplete and
they will be updated upon final approval of this standard.)
Task Group X3T9.2 on Lower-Level Interfaces, which developed this standard,
had the following members:
William E. Burr (Chairman)
John B. Lohmeyer (Vice Chairman)
Ezra R. Alcudia Keith Amundsen (Alt)
J. L. Amstutz Karen Anneberg (Alt)
Bob Bender Charles Brill (Alt)
John Blagaila Larry Boucher (Alt)
Tom Briggs Paul Clement (Alt)
David T. Cornaby George E. Clark (Alt)
David F. Craft, Jr. Steve Cooper (Alt)
Jay Cunningham Gary Crowell (Alt)
Willard S. Davidson Jon Ericson (Alt)
Terry Dawson Tom Fiers (Alt)
Phil Devin Stephen Fitzgerald (Alt)
Louis C. Domshy Marty Francis (Alt)
Norm Dornseif William Homans (Alt)
Alan Ebright J. V. Howell (Alt)
Anita Freeman Skip Kilsdonk (Alt)
Abe Gindi Jim Korpi (Alt)
William A. Horton Lawrence J. Lamers (Alt)
Frank Krulc Keith Mueller (Alt)
Patrick E. Lannan Don Nanneman (Alt)
Daniel Loski Doug Nolff (Alt)
William C. Mavity Richard Reiser (Alt)
Gene Milligan William H. Roberts (Alt)
Bob Mortensen Floyd E. Ross (Alt)
Gary S. Robinson D. Michael Robinson (Alt)
Don Rodgers Jay Seashore (Alt)
Arnold J. Roccati Chuck Spatafore (Alt)
Jack Schiffhauer Jeff Stai (Alt)
Ralph H. Schultz Paul Stavish (Alt)
Moshe Segal
Delbert L. Shoemaker
Tim Slaton
Robert N. Snively
Adrienne Turenne
Norm Zimmerman
T A B L E O F C O N T E N T S
1. Scope...................................................................8
2. Referenced Standard.....................................................9
3. Glossary and Conventions................................................9
3.1 Glossary...........................................................9
3.2 Editorial Conventions.............................................11
4. Physical Characteristics...............................................11
4.1 Physical Description..............................................11
4.2 Cable Requirements................................................11
4.3 Connector Requirements............................................12
4.4 Electrical Description............................................22
4.5 SCSI Bus..........................................................25
4.6 SCSI Bus Signals..................................................27
4.7 SCSI Bus Timing...................................................30
5. Logical Characteristics................................................31
5.1 SCSI Bus Phases...................................................31
5.2 SCSI Bus Conditions...............................................38
5.3 SCSI Bus Phase Sequences..........................................40
5.4 SCSI Pointers.....................................................42
5.5 Message System Specification......................................42
6. SCSI Commands .........................................................49
6.1 Command Implementation Requirements...............................50
6.2 Command Descriptor Block........................................50.1
6.3 Command Examples..................................................55
7. Command Descriptions for All Device Types..............................57
7.1 Group 0 Commands for All Device Types.............................57
7.2 Group 1 Commands for All Device Types.............................76
7.3 Group 2 Commands for All Device Types.............................79
7.4 Group 3 Commands for All Device Types.............................79
7.5 Group 4 Commands for All Device Types.............................79
7.6 Group 5 Commands for All Device Types.............................79
7.7 Group 6 Commands for All Device Types.............................79
7.8 Group 7 Commands for All Device Types.............................79
8. Command Descriptions for Direct-Access Devices.........................80
8.1 Group 0 Commands for Direct-Access Devices........................80
8.2 Group 1 Commands for Direct-Access Devices.......................104
9. Group 0 Command Descriptions for Sequential-Access Devices............117
10. Group 0 Command Descriptions for Printer Devices......................140
11. Group 0 Command Descriptions for Processor Devices....................152
12. Command Descriptions for Write-Once Read-Multiple Devices.............155
12.1 Group 0 Commands for Write-Once Read-Multiple Devices...........155
12.2 Group 1 Commands for Write-Once Read-Multiple Devices...........164
13. Command Descriptions for Read-Only Direct-Access Devices..............170
13.1 Group 0 Commands for Read-Only Direct-Access Devices............170
13.2 Group 1 Commands for Read-Only Direct-Access Devices............171
14. Status ...............................................................172
L I S T O F F I G U R E S
4-1 Nonshielded SCSI Device Connector.....................................13
4-2 Nonshielded Cable Connector...........................................15
4-5 Termination for Single-Ended Devices..................................24
4-6 Termination for Differential Devices..................................24
4-7 Differential Driver Protection Circuit (Optional).....................24
4-8 SCSI ID Bits..........................................................25
4-9 Sample SCSI Configurations............................................26
5-1 Phase Sequences without Arbitration...................................41
5-2 Phase Sequences with Arbitration......................................41
5-3 Simplified SCSI System................................................42
Appendixes
Appendix A................................................................174
SCSI Signal Sequence Example
Appendix A Figures
A1: SCSI Timing Chart ...............................................175
Appendix B................................................................177
Typical Bus Phase Sequence
Appendix C................................................................179
SCSI System Operation
C1. Host Memory / Host Adapter / SCSI Controller Relationship........179
C2. SCSI READ Command Example........................................180
C3. I/O Channel Concept..............................................181
Appendix C Figures
C1: Snapshot Prior to Initial Selection..............................182
C2: Snapshot Prior to Data Transfer..................................183
Appendix D................................................................184
Recommended Shielded Connectors
D1. Shielded Connector, Alternative 1................................184
D2. Shielded Connector, Alternative 2................................184
D3. EUROCARD Boxes...................................................184
Appendix D Figures
D1: Female Shielded SCSI Cable Connector, Alternative 1..............185
D2: Male Shielded SCSI Device Connector, Alternative 1...............187
D3: Shielded SCSI Device Connector, Alternative 2....................189
D4: Shielded SCSI Cable Connector, Alternative 2.....................190
Appendix E................................................................193
Conformance
E1. Alternatives.....................................................193
E2. Levels of Conformance............................................193
E3. Options..........................................................194
E4. Statement of Conformance.........................................194
Appendix F................................................................195
Additional Medium Type and Density Code Standards
Appendix G................................................................197
Future Standardization
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