ISO 9316:1989

Information processing systems — Small Computer System Interface (SCSI)

Systèmes de traitement de l'information — Interface système pour petits ordinateurs (SCSI)

General Information

• Status: Withdrawn
• Publication Date: 26-Jul-1989
• Withdrawal Date: 26-Jul-1989
• ICS: 35.200 - Interface and interconnection equipment
• Technical Committee: ISO/IEC JTC 1/SC 25 - Interconnection of information technology equipment
• Drafting Committee: ISO/IEC JTC 1/SC 25 - Interconnection of information technology equipment
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 02-Nov-1995

Relations

• Revised: ISO/IEC 9316:1995 - Information technology — Small Computer System Interface-2
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL IS0
931 6
STANDARD
First edition
1989-07-1 5
Information processing systems - Small
Computer System Interface (SCSI)
Systèmes de traitement de Sinformation - Interface système pour petits
ordinateurs (SCSI)
Reference number
IS0 9316 : 1989 (E)

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IS0 9316 : 1989 (E)
Contents
Page
1 Scope . 1
*
2 Normative references . 3
3 Definitions, abbreviations and conventions . 5
3.1 Definitions . 5
3.2 Abbreviations . 5
3.3 Editorial conventions . 6
4 Physical Characteristics . 7
4.1 Physical Description . 7
4.2 Cable Requirements . 7
4.3 Connector Requirements . 7
4.4 Electrical Description . 12
4.5 SCSI Bus . 15
4.6 SCSI Bus Signals . 17
4.7 SCSI Bus Timing . 18
5 Logical characteristics . 21
5.1 SCSI Bus Phases . 21
.................................................................................... 26
5.2 SCSI Bus Conditions
5.3 SCSI Bus Phase Sequences .
5.4 SCSI Pointers . 29
6 SCSI commands . 36
6.1 Command Implementation Requirements . 36
6.2 Command Descriptor Block (CDB) . 37

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IS0 9316 : 1989 (E)
6.3 Command Examples . 41
7 Command descriptions for all device types . 43
7.1 Group O Commands for All Device Types . 43
7.2 Group 1 Commands for All Device Types . 59
7.3 Group 2 Commands for All Device Types . 62
.................................................. 62
7.4 Group 3 Commands for All Device Types
7.5 Group 4 Commands for All Device Types . 62
7.6 Group 5 Commands for All Device Types . 62
All Device Types . 62
7.7 Group 6 Commands for
7.8 Group 7 Commands for All Device Types . 62
8 Command descriptions for direct-access devices . 63
8.1 Group O Commands for Direct-Access Devices . 63
8.2 Group 1 Commands for Direct-Access Devices . 86
9 Group O command descriptions for sequential-access devices . 99
9.1 REWIND Command . 100
9.2 READ BLOCK LIMITS Command . 101
9.3 READ Command . 102
9.4 WRITE Command . 103
9.5 TRACK SELECT Command . 104
9.6 READ REVERSE Command . 105
9.7 WRITE FILEMARKS Command . 106
9.8 SPACE Command . 107
9.9 VERIFY Command . 108
9.10 RECOVER BUFFBRED DATA Command . 109
9.11 MODE SELECT Command . 110
9.12 RESERVE UNIT and RELEASE UNIT Commands . 113
9.13 ERASE Command . 114
9.14 MODE SENSE Command . 115
9.15 LOADKJNLOAD Command . 117
9.16 PREVENT/ALLOW MEDIUM REMOVAL Command . 118
iii

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IS0 9316 : 1989 (E)
10 Group O command descriptions for printer devices . 119
10.1 FORMAT Command . 120
10.2 PRINT Command . 121
10.3 SLEW AND PRINT Command . 121
10.4 %USH BUFFER Command . 122
105 RECOVER BUFFERED DATA Command . 123
10.6 MODE SELECT Command . 124
10.7 RESERVE U" and RELEASE UNIT Commands . 125
10.8 MODE SENSE Command . 126
10.9 STOP PRINT Command . 128
11 Group O command descriptions for processor devices . 129
11.1 RECEIVE Command . 130
11.2 SEND Command . 130
12 Command descriptions for write-once read-multiple devices . 132
12.1 Group O Commands for Write-Once Read-Multiple Devices . 132
13 Command descriptions for read-only direct-access devices . 147
13.1 Group O Commands for Read-Only Dkect-Access Devices . 147
13.2 Group 1 Commands for Read-Only Direct-Access Devices . 148
14 Status . 149
Annar«r
SCSI Signal !kquence Example . 151
A
Typical Bus Phase Sequence . 155
B
..
C SCSI System Operation . 157
D Recommended Shielded Connectors . 161
E Conformance . 168
Additionai Medium Type and Density Code Standards . 169
F
iv

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IS0 9316 : 1989 (E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 technical committees. Each member
body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission (IEC) on all
matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
IS0 Council. They are approved in accordance with IS0 procedures requiring at
the
least 75 % approval by the member bodies voting.
International Standard IS0 9316 was prepared by Technical Committee ISO/TC 97,
information processing systems.
Annexes A, B, C, D, E and F are for information only.
O IS0 1989
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any
means, electronic or mechanical, including photocopying and microfilm, without permission in
writing from the publisher.
International Organization for Standardization
Case postale 56 CH-I21 1 Genève 20 Switzerland
Printed in Switzerland
V

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IS0 9316 : 1989 (E)
INTERNATIONAL STANDARD
Information processing systems - Small Computer
System Interface (SCSI)
1 Scope
This International Standard provides the mechanical, electrical, and functional requirements for a small computer
input/output bus and command sets for peripheral device types commonly used with small computers.
The small computer system interface, described in this International Standard, is a local I/O bus that can be operated at
data rates up to 4 Mbytes/s depending upon circuit implementation choices. The primary objective of the interface is to
provide host computers with device independence within a class of devices. Thus, different disk drives, tape drives,
printers, and even communication devices can be added to the host computer(s) without requiring modifications to
generic system hardware or software. Provision is made for the addition of nongeneric features and functions through
vendor unique fields and codes.
The interface uses logical rather than physical addressing for all data blocks. For direct access devices, each logical unit
may be interrogated to determine how many blocks it contains. A logical unit may coincide with all or part of a
peripheral device.
Provision is made for cable lengths up to 25 m using differential drivers and receivers. A single-ended driver and
receiver configuration is defined for cable lengths of up to 6 m and is primarily intended for applications within a
cabinet.
The interface protocol includes provision for the connection of multiple initiators (SCSI devices capable of initiating an
operation) and multiple targets (SCSI devices capable of responding to a request to perform an operation). Optional
distributed arbitration (i.e., bus-contention logic) is built into the architecture of SCSI. A priority system awards inter-
face control to the highest priority SCSI device that is contending for use of the bus. The time to complete arbitration is
independent of the number of devices that are contending and can be completed in less than io ps.
The physical characteristics are described in clause 4. There are two electrical alternatives: single-ended and differen-
tial. Single-ended and differential devices are electricaily different and shall not be mixed on the same bus. In addition,
there are several options: shielded or unshielded connectors may be used and parity may or may not be implemented.
Clause 5 describes the logical characteristics of the interface. An arbitration option is defined to permit multiple in-
itiators and to permit concurrent I/O operations. Ail SCSI devices are required to be capable of operating with the
defined asynchronous transfer protocol. In addition, an optional synchronous transfer protocol is defined. Clause 5 also
specifies a message protocol for control of the interface. In most cases, messages are not directly apparent to the host
computer software. Only one message, COMMAND COMPLETE, is mandatory; all others are optional and are not
necessarily implemented. Note that some options (e.g., synchronous transfer) require the implementation of certain
messages.
The SCSI command structure is specified in clause 6. Commands are classified as mandatory (M), extended (E), op-
tional (O), or vendor unique (V). SCSI devices shall implement all mandatory commands defined for the appropriate
device type and may implement other commands as weli. Extended SCSI devices shali implement all extended plus all
mandatory commands and may implement other commands as weli. Extended SCSI devices contain commands that
facilitate the writing of self-configuring software drivers that can “discover” all necessary attributes without prior
knowledge of specific peripheral characteristics (such as storage capacity). Extended commands for direct access
devices also implement a very large logical block address space (232 blocks although mandatory commands for direct
1i
access devices implement a somewhat smaller logical block address space (2 blocks).
1

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IS0 9310 : 1989 (E)
Clause 7 specifies those commands that have a consistent meaning for aii device types.
Clauses 8 through 13 contain commands for direct-access (e.g., magnetic disk), sequential-access (e.g., magnetic tape),
printer, processor, write-once-read-multiple (e.g., optical disk), and read-only direct-access devices, respectively. The
commands in each of these clauses are unique to the device type, or they have interpretations, fields, or features that are
specific for the device type. Thus, for example, although the WRITE command is used for several device types, it has a
somewhat different form for each type, with different parameters and meanings. Therefore, it is specified separately for
each device type.
Clause 14 describes the status byte for ali device types. Status is returned by targets at the end of each command.
2

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IS0 9316 : 1989 (E)
2 Normative references
The following standards contain provisions, which through reference in this text, constitute provisions of this Internation-
al Standard. At the time of publication, the editions indicated were valid. Ali standards are subject to revision, and par-
ties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most
recent editions of the standards listed below. Members of IEC and IS0 maintain registers of currently valid Internation-
al Standards.
IS0 84821987, Information processing systems - Data communication - Twisted pair multipoint interconnections.
This International Standard defines codes which controllers may use to identify that storage media conform to the fol-
lowing storage media standards.
IS0 18631976, Information processing - 9-track, 12,7 mm (0.5 in) wide magnetic tape for information interchange
recorded at 32 'pmm (800 'pi).
IS0 37881976, Information processing - 9-track, 12,7 mm (0.5 in) wide magnetic tape for information interchange
recorded at 63 'pmm (I 600 rpi), phase encoded.
IS0 40521986, Information processing - Data interchange on 6,30 mm (0.25 in) magnetic tape cartridge 63 bpmm (I 600
bpi) phase-encoded.
IS0 56521984, Information processing - Ptrack, 147 mm (0.5 in) wide magnetic tape for înformation interchange -- For-
mat and recording, using group coding at 246 cpmm (6 250 cpi).
IS0 565411:1984, Information processing - Data interchange on 200 mm (8 in) flexble disk camidges using two-frequency
recording at 13 262fprad 1, 9 tpmm (48 tpi), on one side - Part I: Dimensional, physical and magnetic characteristics.
IS0 5654121985, Information processing - Data interchange on 200 mm (8 in) jiaible disk carbidges using two-frequency
recording at 13 262 ftpraa!, 1, 9 tpmm (48 tpi), on one side - Part 2: Track format.
IS0 65%11:1985, Information processing - Data interchange on 130 mm (5.25 in) flexible disk cartridges using two-fre-
quency recording at 7 958ftpraa!, 1,9 tpmm (48 pi), on one side - Part I: Dimensional, physical and magnetic characteris-
tics.
IS0 6596121985, Information processing - Data interchange on 130 mm (5.25 in) jlaible disk camidges using two-fre-
quency recording at 7 SSSftpraa!, I,9 tpmm (48 tpi) on one side - Part 2: Track format.
IS0 7065k1985, Information processing - Data interchange on 200 mm (8 in) jïeaible disk cartridges using modified fre-
quency modulation recording at I3 262 Brad, 1,9 tpmm (48 pi), on both sides - Part I: Dimensional, physical and mag-
netic characteristics.
IS0 7065/21985, Information processing - Data interchange on 200 mm (8 in) flexible disk carbidges using modified fre-
quency modulation recording at 13 262ftprad 1,9 tpmm 48 (tpi), on both sides - Part 2: Track format.
IS0 7487/1:1985, Information processing - Data interchange on I30 mm (5.25 in) flexible disk cam'dges using modified
frequency modulation recording at 7 958 ftpr& 1,9 tpmm (48 tpi), on both sides - Part 1: Dimensional, physical and
magnetic characteristics.
IS0 7487121985, Information processing - Data interchange on 130 mm (5.25 in) flexible disk camidges using modified
frequency modulation recording at 7 958ftpra4 1,9 tpmm (48 tpi), on both sides - Part 2: Track format.
IS0 7487/3:1986, Information processing - Data interchange on 130 mm (5.25 in) freirible disk camidges using modified
7 958ftpra4 1,9 tpmm (48 tpi), on both sides - Part 3: Tmck fmat B.
frequency modulation recording at
IS0 8063/1:1986, Information processing - Data interchange on 630 mm (0.25 in) wide magnetic tape camldge using
IMFM recording at 252ftpmm (6 400ftpi) - Part I: Mechanical, physical and magnetic propem'es.
3

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IS0 9316 : 1989 (E)
IS0 8063/2:1986, Information pmessing - Data interchange on 430 mm (0.25 in) wide magnetic tape cartridge using
IMFM recording at 252 ftpmm (6 400 fipi) - Part 2: Tmck format and method of recording for data interchange in
startlstop mode.
IS0 8378/1:1906, InfoImatioil processing - Data interchange on 130 mm (5.25 in) frexible disk cartridges using modified
frequency mohtlatioI, recording at 7 958 ftpmd, 3,8 tpmm (96 pi), on both sides - Part I: Dimensional, physical and
magnetic characteristics.
IS0 8378/2:1986, Information processing - Data interchange on 130 mm (5.25 in) flexible disk carhidges using modified
frequency modukrliorr mcording at 7 958Jlpr4 3,8 tpmm (% îpi), on boîh sides - Part 2: Track format A.
IS0 û37~.1986, Infovmcrtion processing - Data interchange on 130 mm (5.25 in) flexibbre disk cartridges using modified
frequency modulation recording at 7 958fiprd $8 tpmm (96 tpi), on both sides - Part 3: Track format B.
Is0 8462W986, Information processing - Data Interchange on 430 mm (0.25 in) magnetic tape cartridge using GCR
recording at 394ftpmm (10 O00 hi)), 39 cpmm (1 O00 cpi) - Part I: Mechanical, physical and magnetic propeniès.
IS0 8462/2:1986, Informaiion processing - Data Interchange on 430 mm (0.25 in) magnetic tape cartridges using GCR
recording at 394ftpmm (10 mftpi), 39 cpmm (I O00 cpi) - Part 2: Streaming mode.
IS0 8630/1:1987, Information processing -- Data interchange on 130 mm (5.25 in) flexible disk cartridges using modified fre-
quency modiùation recording at 13 262 ftprad, on 80 tracks on each side - Part 1: Dimensional, physical and magnetic
chamcteristics.
IS0 8630/2:1987, Information processing -- Data interchange on 130 mm (5.25 in) flm-ble disk cartridges using modified fre-
ai 13 262 &rad, on 80 tracks on each side - Part 2: Track format A for 77 tracks.
quency modulation recording
IS0 86301331987, Information processing -- Data interchange on 130 mm (5.25 in) flexible disk camidges using modified Fe-
quency modulation recording at 13 262ftPrad on 80 tracks on each side - Part 3: Track format B for 80 tracks.
IS0 886011:1987, Information processing - Data interchange on 90 mm (3.5 in) flexible disk cattridges using modified fre-
quency modulation recording ai 7 958fprad on 80 tracks on each side - Part I: Dimensional, physical and magnetic
characteristics.
IS0 8860121987, Information processing -- Data interchange on 90 mm (3.5 in) flexible disk cartridges using modified fre-
quency modulation recordiltg at 7 958ftprad on 80 tracks on each side - Part 2: Track format.
4

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IS0 9316 : 1989 (E)
~
I
3 Definitions, abbreviations and conventions
3.1 Definitions
For the purposes of this International Standard the following definitions apply.
3.1.1 byte: In this standard, this term indicates an %bit (octet) byte.
3.1.2 command descriptor block (CDB): The structure used to communicate requests from an initiator to a target.
3.13 connect: The function that occurs when an initiator selects a target to start an operation.
3.1.4 disconnect: The function that occurs when a target releases control of the SCSI bus, allowing it to go to the BUS
FREE phase.
3.15 initiator: An SCSI device (usually a host system) that requests an operation to be performed by another SCSI
device.
3.1.6 INTERMEDIATE status: A status code sent from a target to an initiator upon completion of each command in a
set of linked commands except the last command in the set.
@
3.1.7 logical unit: A physical or virtual device addressable through a target.
3.1.8 logical unit number: An encoded three-bit identifier for the logical unit.
3.1.9 one: A true signal value.
3.1.10 peripheral device: A peripheral that can be attached to an SCSI device (e.g., magnetic-disk, printer, optical-disk,
or magnetic-tape).
3.1.11 reconnect: The function that occurs when a target selects an initiator to continue an operation after a disconnect.
3.1.12 reserved The term used for bits, bytes, fields, and code values that are set aside for future standardization.
3.1.13 SCSI address: The octal representation of the unique address (0-7) assigned to an SCSI device. This address
would normally be assigned and set in the SCSI device during system installation.
3.1.14 SCSI ID: The bit-significant representation of the SCSI address referring to one of the signal lines DB(7-0).
3.1.15 SCSI device: A host computer adapter or a peripheral controller or an intelligent peripheral that can be attached
to the SCSI bus.
3.1.16 signal assertion: The act of driving a signal to the true state.
3.1.17 signal negation: The act of driving a signal to the false state or allowing the cable terminators to bias the signal to
the false state (by placing the driver in the high impedance condition).
3.1.18 signal release: The act of allowing the cable terminators to bias the signal to the false state (by placing the driver
in the high impedance condition).
3.1.19 status: One byte of information sent from a target to an initiator upon completion of each command.
3.130 targek An SCSI device that performs an operation requested by an initiator.
3.1.21 vendor unique: In this standard, this term indicates bits, fields, or code values that are vendor specific and are
not defrned by this standard.
3.122 zero: A false signal value.
3.2 Abbreviations
33.1 LSB. Least significant byte.
5

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.IS0 9316 : 1989 (E)
32.2 LüN. Logical unit number.
323 MSB. Most significant byte.
33 Editorial conventions
Certain words, terms, and phrases used in this standard have a specific meaning beyond the normal English meaning.
These words, terms, and phrases are defined either in the definitions (see 3.1) or in the text where they fist appear (e.g.,
Arbitration Delay, see 4.7.1). Names of signals, phases, conditions, messages, commands, statuses, and sense keys are in
ali uppercase (e.g., REQUEST SENSE). Lower case is used for words having the normal English meaning.
Hexidecimal numbers are indicated by the digits O, 1,2,3,4,5,6,7,8,9, A, B, C, D, E and F foliowed by the lower case
"h" (e. g. 3F6Ah). AU other numbers are decimal values.
6

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IS0 9316 : 1989 (E)
4 Physical Characteristics
This section contains the physical defuiition of the SCSI. The connectors, cables, signals, terminators, and bus teg
needed to implement SCSI are covered.
4.1 Physical Description
SCSI devices are daisy-chained together using a common cable. Both ends of the cable are terminated. All signals are
common between all SCSI devices. Two driverheceiver alternatives are available:
6 m (primarily for connection
Single-ended drivers and receivers, which allow a maximum cable length of
a)
within a cabinet).
Differential drivers and receivers, which allow a maximum cable length of 25 m (primarily for connection out-
b)
side of a cabinet).
42 Cable Requirements
An ideal impedance match with cable terminators implies a cable characteristic impedance of 132 Cl (singled-ended op-
tion) or 122 fl (differential option). In general, cables with this high of a characteristic impedance are not available;
however, impedances that are somewhat lower are satisfactory. A characteristic impedance of 100 s1 2 10% is recom-
@
mended for unshielded flat or twisted pair ribbon cable. A characteristic impedance greater than 90 Cl is preferred for
shielded cables; however, most available cables have a somewhat lower characteristic impedance. To minimize discon-
tinuities and signal reflections, cables of different impedances should not be used in the same bus. Implementations may
require trade-offs in shielding effectiveness, cable length, the number of loads, transfer rates, and cost to achieve satis-
factory system operation.
A mininimum conductor size of nominal cross section 0,080 42 mm2 shall be employed to minimize noise effects and en-
sure proper distribution of optional terminator power.
42.1 Single-Ended Cable
A 50-conductor flat cable or 25-signal twisted- pair cable shall be used. The maximum cable length shall be 6 m.
A stub length of no more than 0,l m is allowed off the mainline interconnection within any connected equipment.
SCSI bus termination may be internal to the SCSI devices that are at the ends of the cable.
422 Differentia1 Cable
A 50-conductor cable or 25-signal twisted-pair cable shail be used. The maximum cable length shall be 25 m.
A stub length of no more than 0,2 m is allowed off the mainline interconnection within any connected equipment.
SCSI bus termination may be internal to the SCSI devices that are at the ends of the cable.
43 Connector Requirements
Nonshielded connectors are specified. The nonshielded connectors are typicaily used for in-cabinet applications.
Annex D defines recommended shielded connectors and their pin assignments. These connectors are typically used for
external applications where electromagnetic compatibility (EMC) and electrostatic discharge (ESD) protection may be
required. Either type of connector may be used with the single-ended or differential drivers.
The nonshielded SCSI device connector (figure 1) shall be a 50-conductor connector consisting of two rows of 25 male
contacts with adjacent contacts 2,54 mm (0,l in) apart. A shroud and header body should be used. The nonmating por-
tion of the connector is shown for reference only.
be a 50-conductor connector consisting of two rows of 25 female con-
The nonshielded cable connector (figure 2) shali
tacts with adjacent contacts 554 mm (0,l in) apart. It is recommended that keyed connectors be used.
7

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IS0 9316 : 1989 (E)
x -x
Note : Straight
through header
may also be used
3
3
Note : Shrouded header
(recommended)
O O
h
-
Dimensions mm in Comments
D1 2,54 0,100
D2 82,50 3,260 Reference only
D3 2,54 0,100
D4 8,89 0,350 Reference only
D5 72,64 2,860 Reference only
D6 78,74 3,100 Reference only
D7 13,94 0,549 Reference only
D8 4,19 f 0,25 0,165 f 0,Ol
D9 6,lO 0,240
D10 6,60 0,260 Reference only
NOTES :
1) Two rows of twenty five contacts on 2,54 mm (0,100 in) spacing = 60,96 mm
(2,400 in).
2) Tolerances f 0,127 mm (0,005 in) non-cumulative, unless specified otherwise.
Figure 1 - Nonshielded SCSI Device Connector
8

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IS0 9316 : 1989 (E)
Even contacts
are not shown
Contact 1 Contact 50
......................
c2
Dimensions
mm I in I Comments I
2,54 O, 100
60,96
2,400
2,54 O, 100
3,30 0,130
32,39
1,275
C6 68,07
2,680
c7 6,lO
0,240
C8 7,62 0,300 max.
NOTES :
1) Fifty contacts on 1,27 mm (0,05 in) staggered spacing = 62,23 mm (2,450 in)
[reference only].
f 0,127 mm (0,005 in) non-cumulative, unless specified otherwise.
2) Tolerances
...