Seagate ST11200 User manual

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Disc Drive SCSI-2/SCSI-3 Interface
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Family Models:
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ST11200, ST12400, ST12400 Wide,
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ST3600, ST3610,
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ST31200, ST31200 Wide,
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ST32430, ST32430 Wide, ST15230,
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ST3655, ST11950, ST11950Wide,
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ST12450 Wide, ST12550,
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ST12550 Wide, ST15150,
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ST15150 Wide, ST31250
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ST31250 Wide, ST32550
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ST32151, ST31051
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ST32550 Wide, ST410800
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ST34371
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Product Manual, Volume 2; Version 2
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Disc Drive SCSI-2/SCSI-3 Interface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Family Models:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST11200, ST12400, ST12400 Wide,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST3600, ST3610,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST31200, ST31200 Wide,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST32430, ST32430 Wide, ST15230,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST3655, ST11950, ST11950Wide,
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ST12450 Wide, ST12550,
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ST12550 Wide, ST15150,
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ST15150 Wide, ST31250
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ST31250 Wide, ST32550
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ST32151, ST31051
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ST32550 Wide, ST410800
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ST34371
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Product Manual, Volume 2; Version 2
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1995 SeagateTechnology, Inc.All rights reserved
Publication Number: 77738479, Rev E
January 1995
Seagate, SeagateTechnologyand the Seagate logo are registered trademarks of SeagateTechnology,
Inc.HAWKTM, SeaFAX,SeaFone, SeaTDDandSeaBOARDare trademarks of SeagateTechnology,
Inc. Other product names are registered trademarks or trademarks of their owners.
Seagate reserves the right to change, without notice, product offerings or specifications. No part of this
publication may be reproduced in any form without written permission of SeagateTechnology, Inc.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2;Ver. 2), Rev. E v
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Revision Status Summary Sheet
Revision Authority Date Signature Sheets Affected
A Issue 12/18/92 D. Ashby/J. Averyt 1/1, 1 thru 257.
B PLD:83345 8/18/93 1/1, 1 thru 4, 4.1, 5 thru 193
deleted shs 194 thru 257.
Technical changes on pages
5, 9, 10, 78, 93, 94, 104 - 107,
109, 136, 139 - 142, 144, 147,
149, 161 - 164, 166, 167, 181,
185 thru 193.
C PLD: 83534 93 Oct. 19 SS 1/1, Revised sheets v thru ix, 1 thru
193.(Technical changes on pages
v, vii, 1, 4, 5, 7, 8, 47, 70, 73, 78, 79,
83, 84, 86, 87, 90, 91, 93, 94, 104,
105,107, 112, 114, 119,123-131,
136-144, 147-156, 158-160, 162-
170, 176, 178-180, 184, 185, 189
192 and 193).
D PLD:85300 5/26/94 SS 1/1, v thru ix, 1 thru 189; (technical changes
on pages 1, 8, 12, 26, 29, 34, 35, 70, 71, 77,
79, 80, 84, 85, 86, 95, 101, 104, 125, 150,
125, 150, 151, 160, 162, 163 & 164.)
E PLD:87127 01/24/95 1/1, v thru ix, 1 thru 187; deleted shs188 and 189.
Renumbered pages 94 thru 187. (Technical
changes on pages vi, vii, ix, 1, 2, 18, 21, 25, 26,
32, 33, 47, 50, 57, 68, 72, 74, 75, 77, 78, 79, 87,
88 - 90, 94, 105, 110, 114, 122, 124, 126, 127,
133, 135, 136, 139, 140, 143, 150, 152, 154,
158, 160, 162 - 164, 168 - 175, 178, 187.

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Table of contents
1.0 Interface requirements ............................................................................................................ 1
1.1 How to use this interface manual .................................................................................. 1
1.2 General interface description ........................................................................................ 1
1.3 Physical interface characteristics.................................................................................. 3
1.4 Summary of SCSI commands and messages............................................................... 4
2.0 SCSI bus................................................................................................................................... 6
2.1 SCSI bus signals .......................................................................................................... 7
2.1.1 Drive select ...................................................................................................... 8
2.1.2 Signal values.................................................................................................... 8
2.1.3 OR-Tiedsignals ............................................................................................... 8
2.1.4 Signal sources ................................................................................................. 8
2.2 SCSI bus timing ............................................................................................................ 9
2.2.1 Arbitration delay ............................................................................................... 9
2.2.2 Assertion period ............................................................................................... 9
2.2.3 Bus Clear delay................................................................................................10
2.2.4 Bus Free delay.................................................................................................10
2.2.5 Bus Set delay...................................................................................................10
2.2.6 Bus Settle delay ...............................................................................................10
2.2.7 Cable Skew delay ............................................................................................ 10
2.2.8 Data Release delay..........................................................................................10
2.2.9 Deskew delay ..................................................................................................10
2.2.10 Disconnection delay......................................................................................... 10
2.2.11 Hold time..........................................................................................................10
2.2.12 Negation period................................................................................................ 10
2.2.13 Reset Hold time ...............................................................................................11
2.2.14 SelectionAbort time .........................................................................................11
2.2.15 SelectionTimeout delay ...................................................................................11
2.2.16 Transfer Period(negotiated by SDTR message)...............................................11
2.3 Fast synchronous transfer option timing .......................................................................11
2.3.1 Fast Assertion period ....................................................................................... 11
2.3.2 Fast Cable Skew delay ....................................................................................11
2.3.3 Fast Deskew delay...........................................................................................11
2.3.4 Fast Hold time..................................................................................................11
2.3.5 Fast Negation period........................................................................................11
3.0 Logical characteristics ............................................................................................................ 12
3.1 SCSI bus phases ..........................................................................................................12
3.1.1 Bus Free phase................................................................................................12
3.1.2 Arbitration phase ..............................................................................................13
3.1.3 Selection phase ...............................................................................................13
3.1.4 Reselection phase ........................................................................................... 15
3.1.5 Information Transfer phases ............................................................................ 16
3.1.6 Command phase.............................................................................................. 18
3.1.7 Data phase ......................................................................................................18
3.1.8 Status phase (see Section 4.3) ........................................................................18
3.1.9 Message phase................................................................................................19
3.1.10 Signal Restrictions Between phases...... ..........................................................19

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Table of contents
3.2 SCSI bus conditions......................................................................................................20
3.2.1 Attention conditions (see Unit Attention Condition, 4.6).................................... 20
3.2.2 Reset condition ................................................................................................21
3.2.3 ContingentAllegiance condition .......................................................................21
3.3 SCSI bus phase sequences.......................................................................................... 21
3.3.1 Nonarbitrating system ...................................................................................... 21
3.3.2 Arbitrating systems .......................................................................................... 21
3.3.3 All systems....................................................................................................... 22
3.4 SCSI pointers................................................................................................................ 23
3.4.1 Current pointers ...............................................................................................24
3.4.2 Saved pointers ................................................................................................. 24
3.5 Message system specification ...................................................................................... 24
3.5.1 General message protocol ...............................................................................25
3.5.2 Messages - general .........................................................................................25
3.5.3 Message details ...............................................................................................27
3.5.3.1 One and Two Byte message ............................................................ 27
3.5.3.2 Extended message .......................................................(01h) ......... 35
4.0 SCSI commands ...................................................................................................................... 42
4.1 Commandimplementationrequirements ...................................................................... 42
4.1.1 Reserved .........................................................................................................42
4.2 Command descriptor block (CDB) ................................................................................42
4.2.1 Operation code ................................................................................................ 43
4.2.2 Logical Unit Number (LUN) ..............................................................................44
4.2.3 Logical Block Address......................................................................................45
4.2.4 Relative Address Bit.........................................................................................45
4.2.5 Transfer Length................................................................................................45
4.2.6 Control Byte ..................................................................................................... 46
4.3 Status ...........................................................................................................................46
4.4 Command examples ..................................................................................................... 48
4.4.1 Single Command example ............................................................................... 48
4.4.2 Disconnect example......................................................................................... 50
4.5 Timing examples........................................................................................................... 52
4.6 Unit attention condition..................................................................................................67
4.7 Queued I/O processes..................................................................................................68
4.7.1 Untaggedqueuing............................................................................................68
4.7.2 Tagged queuing ...............................................................................................68
4.8 ParameterRounding.....................................................................................................70
4.9 Command Processing considerations and exception conditions...................................70
4.9.1 ProgrammableOperatingdefinition.................................................................. 70
4.9.2 Incorrect initiator connection ............................................................................71
4.9.3 Selection of an Invalid Logical unit ................................................................... 71
5.0 Command descriptions...........................................................................................................72
5.1 Command descriptions for all device types...................................................................72
5.1.1 Group 0 commands for all device types ...........................................................72
5.1.1.1 Test Unit Ready.............................................................(0h) ........... 72
5.1.1.2 Request Sense command.............................................(03h) ......... 73
5.1.1.2.1 Deferred errors.................................................................81
5.1.1.3 Inquiry command ..........................................................(12h) ......... 82
5.1.1.3.1 Vital product data pages...................................................86
5.1.1.4 Copy command.............................................................(18h) .........95
5.1.1.5 Receive Diagnostic results command ...........................(1Ch)......... 95
5.1.1.6 Send Diagnostic command ...........................................(1Dh) .........100

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Table of contents
5.1.2 Group 1 commands for all device types ......................................................... 103
5.1.2.1 Compare command ......................................................(39h) ....... 103
5.1.2.2 Copy and verify command ............................................(3Ah) ....... 103
5.1.2.3 Write Data Buffer command..........................................(3Bh) ....... 103
5.1.2.3.1 Combined Header and Data Mode................(000b) ..... 104
5.1.2.3.2 Write Data Only ............................................................. 105
5.1.2.3.3 Download & Save Microcode Mode ..............(101b) ..... 105
5.1.2.4 Read Data Buffer command..........................................(3Ch)....... 106
5.1.2.4.1 Read Combined Descriptor Header
and Data Mode .............................................(000b) ..... 106
5.1.2.4.2 Read data ...................................................................... 107
5.1.2.4.3 Descriptor mode ...........................................(011b)...... 107
5.1.3 Group 2 Commands for All DeviceTypes....................................................... 108
5.1.3.1 Change Definition command.........................................(40h) ....... 108
5.1.3.2 Log Select command ....................................................(4Ch)....... 109
5.1.3.2.1 Write, Read andVerify Error Counter pages
(code 02, 03, 05h) ......... 116
5.1.3.2.2 Non-Medium Error page ...............................(code 06h) 118
5.1.3.2.3 Cache Statistics page ...................................(code 37h) 118
5.1.3.3 Log Sense command ....................................................(4Dh)....... 119
5.1.3.4 Other Group 2 commands ............................................................. 121
5.1.4 Groups 3 through 5 commands for all device types ....................................... 121
5.1.5 Group 6 commands for all device types ......................................................... 121
5.1.6 Group 7 commands for all device types ......................................................... 121
5.2 Command descriptions for direct access devices ....................................................... 121
5.2.1 Group 0 commands for direct access devices ............................................... 121
5.2.1.1 Rezero Unit command ..................................................(01h) ....... 122
5.2.1.2 Format Unit command ..................................................(04h) ....... 122
5.2.1.3 Reassign Blocks command...........................................(07h). ...... 130
5.2.1.4 Read command ............................................................(08h) ....... 132
5.2.1.5 Write command.............................................................(0Ah) ....... 134
5.2.1.6 Seek command.............................................................(0Bh) ....... 135
5.2.1.7 Mode Select (6) command ............................................(15h) ....... 136
5.2.1.8 Reserve command........................................................(16h) ....... 140
5.2.1.9 Release command ........................................................(17h). ...... 142
5.2.1.10 Mode Sense (6) command............................................(1Ah) ....... 143
5.2.1.11 Start Stop Unit command ..............................................(1Bh) ....... 169
5.2.1.12 Prevent/Allow Medium Removal command...................(1Eh). ...... 170
5.2.2 Group 1 command for direct access devices ................................................. 170
5.2.2.1 Read Capacity command..............................................(25h) ....... 170
5.2.2.2 Read Extended command.............................................(28h) ....... 172
5.2.2.3 Write Extended command .............................................(2Ah) ....... 174
5.2.2.4 Seek Extended command .............................................(2Bh) ....... 175
5.2.2.5 Write andVerify command ............................................(2Eh) ....... 176
5.2.2.6 Verify command ............................................................(2Fh) ....... 177
5.2.2.7 Synchronize Cache command ......................................(35h) ....... 178
5.2.2.8 Read Defect Data command.........................................(37h) ....... 179

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Table of contents
5.2.2.9 Read Long command....................................................(3Eh) ....... 181
5.2.2.10 Write Long command ....................................................(3Fh) ....... 183
5.2.2.11 Reserve (10) command ................................................(56h) ....... 184
5.2.2.12 Release (10) command.................................................(57h) ....... 185
5.2.2.13 Mode Select (10) command ..........................................(55h) ....... 186
5.2.2.14 Mode Sense (10) command..........................................(5Ah) ....... 186
6.0 SeagateTechnical Support Service ..................................................................................... 187

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1.0 Interface requirements
1.1 How to use this interface manual
This specification is designed to provide a universal detailed description of the SCSI interface for those disc
drive products whose Product Manuals (Volume 1) do not contain the details of how the SCSI interface is
implemented by that drive.
Note: Volume 1 Product Manuals have tables in Section 11 that specify which SCSI-1 or SCSI-2/SCSI-
3 features they implement, what the default parameters are for the various features they implement
and which parameters are changeable and which are not.
No method exists at present to inform an initiator if a target supports "SCSI-3" features as opposed
to only SCSI-2 features.A few "SCSI-3" features are supported by Seagate drives,but no attempt has
been made herein to differentiate between SCSI-2 and "SCSI-3" features. Therefore, when an Inquiry
command reports what the ANSI approved version of the drive is, it reports either SCSI-1 or SCSI-2,
where "SCSI-2" means SCSI-2 features plus some "SCSI-3" features.
No attempt is made in this universal specification to specify which descriptions or tables apply to SCSI-1 and
which to SCSI-2 or SCSI-3.The combination of this general specification with the details in the Section 11
tables of the individual drive Product Manual (Volume 1) provides a description of the individual drive imple-
mentation of the SCSI interface.
This interface manual is not intended to be stand-alone text on SCSI-1 or SCSI-2/SCSI-3 features. Refer-
ence must be made back to the individual drive Product Manuals to find out what are SCSI-1 and what are
SCSI-2/SCSI-3features.
Thisspecification isVolume 2 of aset of manualsthat is made upof separatedriveProduct Manuals(Volume
1)andthis manual.ThisVolume 2Manualis referenced by otherVolume 1 ProductManualsrepresenting the
drives listed below.
Product Manuals for the following models reference this volume: ST11200N/ND/NC, ST1980N/ND/NC,
ST1830N,ST1950N, ST3500N,ST3600N, ST3610N/ND/NC,ST12400N/ND/NC,ST12400Wide,ST11900N/
ND/NC, ST31200N/ND/NC, ST31200 Wide, ST11950N/ND, ST11950W/WD, ST12450W/WD,ST12550N/
ND, ST12550W/WD, ST15150N/ND, ST15150W/WD, ST3655N, ST3550W, ST3390N and ST3285N,
ST32430N/ND/NC,ST32430W/WD/WC,ST15230N/ND/NC,ST31250N/ND,ST31250W/WD/WC,ST32151N,
ST31051N, ST32550N/ND, ST32550W/WD/WC, ST3471N, ST410800N/ND, ST410800W/WD.
1.2 General interface description
This Product Manual describes the SeagateTechnology, Inc.subset of the SCSI (Small Computer Systems
Interface) as implemented on the Seagate built disc drives listed above.The interface is compatible with the
SCSI Interface Specifications of the ANSI SCSI-1 standard, the ANSI SCSI-2 Standard and the common
command set (CCS) document, Revision 4.B.The disc drives covered by this Product Manual are classified
as “Intelligent” peripherals.

2 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2;Ver. 2), Rev. E
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TheSeagate SCSI interfacedescribedherein consistsofa 9 or18 bit bidirectionalbus (8 data+ 1 parityor16
data + 2 parity) plus 9 control signals supporting multiple initiators, disconnect/ reconnect, self configuring
host software, automatic features that relieve the host from the necessity of knowing the physical architec-
ture of the target (logical block addressing is used), and some other miscellaneous features.
The SCSI physical interface uses either single ended drivers and receivers or differential drivers and receiv-
ers and uses asynchronous or synchronous communication protocols. The bus interface transfer rate for
asynchronous or synchronous is given in individual disc drive Volume 1 Product Manuals.The bus protocol
supports multiple initiators, disconnect/reconnect, additional messages plus 6 byte and 10 byte Command
Descriptor Blocks.
Unless specified otherwise in the individual drive Product Manuals (Vol.1), the disc drive is always a target,
and never an initiator. For certain commands, which may or may not be supported by a particular drive
model, the drive must act as an initiator, but does not otherwise do so. For purposes of this specification,
“disc drive” may be substituted for the word “target” wherever “target” appears.
GLOSSARY
Arbitration - SCSI bus phase wherein SCSI devices try to gain control of the SCSI bus to operate as an
initiator or target (see Section 3.1.2).
Byte - This term indicates an 8 bit hexadecimal construction.
Command Descriptor Block (CDB) - The structure used to communicate requests from an initiator to a
target.
Connect -The function that occurs when an initiator selects a target to start an operation.
Disconnect -The function that occurs when a target releases control of the SCSI bus, allowing it to go to the
Bus Free phase.
FRU (Field Replaceable Unit) - An assembly that is believed faulty based on test results. A value of 00h
indicates an unknown cause or the end of a list of known possible causes. Nonzero values have product
uniquemeanings.
Initiator -A SCSI device (usuallya host system)thatrequests an operationtobe performed by anotherSCSI
device.
Intermediate Status - A status code sent from a target to an initiator upon completion of each command,
except the last command, in a set of linked commands.
I/O Process- AnI/O process consists ofone initial connectionandzeroor more reconnections,all pertaining
to a single command or group of linked commands.More specifically, the connection(s) pertain to a nexus as
defined below in which one or more command descriptor blocks are usually transferred. An I/O process
begins with the establishment of a nexus.An I/O process normally ends with the BUS Free phase following
successful transfer of a COMMAND COMPLETE, ABORT, ABORTTAG, or CLEAR QUEUE message.An I/
O process also ends when a hard RESET condition occurs, an unexpected BUS FREE phase occurs, or
when the BUS FREE phase occurs following a BUS DEVICE RESET message.
I T nexus - A nexus prior to the successful receipt of an IDENTIFY message, at which time the nexus is
changed to an I T L nexus.(See glossary word “Nexus”).
IT L nexus - A nexus that exists between an initiator and a Logical Unit.This relationship replaces the prior
I T nexus. (See glossary word “Nexus”).
IT L Q nexus - A nexus between an initiator, a Logical Unit, and a queue tag following the successful receipt
ofone of theQUEUE messages.This relationship replacesthe priorIT Lnexus. (See glossary word“Nexus”).
Logical Unit - A physical device or virtual device addressable through a target.The disc drive is a target but
also a Logical Unit.
Logical Unit Number- An encodedthree bit identifierfor thelogical unit.ThediscdriveisconsideredLogical
Unit number zero.
LSB - Least significant byte MSB - Most significant byte ms - millisecond
LUN - Logical unit number mm - Millimetre

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nexus - A relationship that begins with the establishment of an initial connection and ends with the comple-
tion of the I/O process.The relationship starts as an association between the initiator and a selected target.
The relationship may be restricted to specify a single logical unit or target routine by the successful transfer
of an IDENTIFY message.The relationship may be further restricted by the successful transfer of a queue
tag message.
ns - Nanosecond
One - A true signal value, (assertion).
Page - Several commands use regular parameter structures that are referred to as pages.These pages are
identified with a value known as a page code.
Queue -This term refers to the command queue used in tagged queuing (see 4.7.2).
Queue Tag - The value associated with an I/O process that uniquely identifies it from other queued I/O
processes on the logical unit for the same initiator.
Reconnect - The function that occurs when a target selects an initiator to continue an operation after a
disconnect.
Reconnection - A reconnection exists from the assertion of the BSY signal in a RESELECTION phase until
the next BUS FREE phase occurs.A reconnection can only occur between a target and an initiator.
Reserved -Theterm used forbits,bytes,fields,and code valuesthat areset aside for futurestandardization.
SCSI Address - The octal representation of the unique address (0-7) assigned to a SCSI device. This
address would normally be assigned and set in the SCSI device during system installation (see individual
disc drive Product Manuals).
SCSI ID -The bit significant representation of the SCSI address referring to one of the signal lines DB(7-0).
SCSI device - A host computer adapter or a peripheral controller or an intelligent peripheral that can be
attached to the SCSI bus.
Signal Assertion -The act of driving a signal to the true state.
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).
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).
xxh - Numbers followed by lower case h are hexadecimal values.All other numbers are decimal values.
Status - One byte of information sent from a target to an initiator upon completion of each command.
Target - A SCSI device that performs an operation requested by an initiator.
us - Microsecond.
Vendor Unique - In this specification, this term indicates bits, fields, or code values that are vendor specific.
Zero - A logical false signal value, (negation).
1.3 Physical interface characteristics
The physical interface characteristics (cables, connectors, electrical descriptions, termination requirements,
etc.)for the drives coveredbythis Interface Manualarefound in eachindividualProduct Manual, sincethese
features are not the same for all drives.

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1.4 Summary of SCSI commands and messages
Following is an alphabetical table listing the SCSI commands described in this manual. Details are given in
Section 5.
Command name Hex code Group Device type Page number
ChangeDefinition 40 2 All 108
Format Unit 04 0 dir. access 122
Inquiry 12 0 All 83
Log Select 4C 2 All 110
Log Sense 4D 2 All 119
Mode Select (6 byte) 15 0 dir. access 136
Mode Select (10 byte) 55 1 dir. access 186
Mode Sense (6 byte) 1A 0 dir. access 143
Mode Sense (10 byte) 5A 1 dir. access 186
Read 07 0 dir. access 132
Read Capacity 25 1 dir. access 170
Read Data Buffer 3C 1 All 107
Read Defect Data 37 1 dir. access 179
Read Extended 28 1 dir. access 172
Read Long 3E 1 dir. access 181
Reassign Blocks 07 0 dir. access 130
Receive Diagnostic Results 1C 0 All 95
Release (6 byte) 17 0 dir. access 143
Release (10 byte) 57 1 dir. access 185
Reserve (6 byte) 16 0 dir. access 142
Reserve (10 byte) 56 1 dir. access 184
Request Sense 03 0 All 74
Rezero 01 0 dir. access 122
Seek 0B 0 dir. access 135
Seek Extended 2B 1 dir. access 175
Send Diagnostics 1D 0 all 100
Start/Stop Unit 1B 0 dir. access 169
Synchronize Cache 35 1 dir. access 178
Test Unit Ready 00 0 All 73
Verify 2F 0 dir. access 177
Write 0A 0 dir. access 134
Write andVerify 2E 1 dir. access 176
Write Extended 2A 1 dir. access 174
Write Long 3F 1 dir. access 182

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Following is an alphabetical summary of the SCSI messages described in this manual. Details are given in
Section 3.5.
Message Name Hex Code Page number
Abort 06 28
AbortTag 0D 29
Bus Device Reset 0C 29
Clear Queue 0E 29
CommandComplete 00 29
Disconnect 04 30
Extended Message 01 40
Identify 80-FF 30
Ignore Wide Residue 23 41
Initiate Recovery 0F not supported
Initiator Detected Error 05 31
Linked Command Complete 0A 31
Linked Command Complete
(with flag) 0B 31
Message Parity Error 09 31
Message Reject 07 32
Modify Data Pointer 01 32, 35 (extended message)
No Operation 08 32
QueueTag Messages 33
Head of QueueTag 21 33
Ordered QueueTag 22 34
Simple QueueTag 20 34
Release Recovery 10 not supported
Restore Pointers 03 34
Save Data Pointers 02 34
Synchronous Data Transfer
Request 01 34, 36 (extended message)
Terminate I/O Process 11 34 (optional)
Wide Data Transfer Request 01 38 (extended meessage)

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2.0 SCSI bus
This manual discusses only the "logical" and timing characteristics of the SCSI system and interface. The
SCSI bus physical characteristics (voltages, connector configurations, pinouts, etc.) are given in the indi-
vidual disc drive Product Manuals (Volume 1) Section“Interface requirements”, which covers all of the inter-
face requirements and SCSI features supported by the drive described in the particular Product Manual
being referenced.
Communication on the SCSI Bus is allowed between only two SCSI devices at a time. Some Seagate drives
support systems with a maximum of eight SCSI devices including the host computer(s) connected to the
SCSIbus. Some Seagate drivessupportsystems with amaximumof sixteen SCSIdeviceson the SCSIbus.
EachSCSI devicehasaSCSI ID Bitassigned as shownin Figure2.0-1.The SCSI IDisassigned byinstalling
from 0 to 3 (8 device systems) jumper plugs or 0-4 (16 device systems) jumper plugs onto a connector in a
binary coded configuration during system configuration. Some drive models have an interface that includes
the SCSI bus ID lines, so that the host can set the drive ID over the interface. See individual disc drive
Product Manual, Section “Option/configuration headers”.
Whentwo SCSI devicescommunicateon theSCSIBus one actsas an initiatorand the otheracts as atarget.
The initiator (typically a host computer) originates an operation and the target performs the operation.The
disc drive always operates as a target, unless specified otherwise (i.e., certain commands are supported) in
the individual drive Product Manual.
DB(7) DB(6) DB(5) DB(4) DB(3) DB(2) DB(1) DB(0) DATA BUS
SCSI ID = 0
SCSI ID = 1
SCSI ID = 2
SCSI ID = 3
SCSI ID = 4
SCSI ID = 5
SCSI ID = 6
SCSI ID = 7
Additional SCSI ID bits for devices that support 16 devices on the SCSI bus.
DB(15) DB(14) DB(13) DB(12) DB(11) DB(10) DB(9) DB(8) DATA BUS
SCSI ID = 8
SCSI ID = 9
SCSI ID = 10
SCSI ID = 11
SCSI ID = 12
SCSI ID = 13
SCSI ID = 14
SCSI ID = 15
Figure 2.0-1. SCSI ID bits

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The Host Adapter/Initiator must be identified by one of the eight SCSI Device Addresses. Make sure that
none of the devices on the SCSI bus have duplicate addresses.
Certain SCSI bus functions are assigned to the initiator and certain SCSI bus functions are assigned to the
target. The initiator will select a particular target. The target will request the transfer of Command, Data,
Status or other information on the data bus.
Information transfers on the data bus are interlocked and follow a defined REQ/ACK Handshake protocol.
One byte of information will be transferred with each handshake. Synchronous data transfers do not require
a one for one interlocking of REQ/ACK signals, but the total number of REQ pulses in a particular data
transfer event must equal the total number of ACK pulses.Synchronous data transfer option is described in
Paragraph 3.5.3.2 and 3.1.5.2.
The disc drive supports single initiator, single target; single initiator, multiple target; multiple initiator, single
target;or multiple initiator, multiple target bus configurations.
2.1 SCSI bus signals
There are ten control and eighteen data signals, as listed below:
• BSY • C/D • MSG • DIFFSENS
• SEL • I/O • REQ • DB(7-0, P); DB(15-8,P1)
•ACK •ATN •RST
Some drive models have a single 80 pin I/O connector that contains additional interface lines that carry drive
configuration select signals.These are peculiar to certain drives and are not SCSI standard signals.These
are described in the drive model'sVolume 1 Product manual, but not here.
The 28 SCSI standard signals are described as follows:
BSY (Busy) - An “OR-tied” signal to indicate the bus is being used.
SEL (Select) - A signal used by an initiator to select a target, or by a target to reselect an initiator.
C/D (Control/Data)- Asignaldrivenbyatargetto indicate whetherControl or Datainformation ison the Data
Bus.Assertion (see Paragraph 2.1.2) indicates Control.
I/O (Input/Output) - A signal driven by a target to control the direction of data movement on the Data Bus
with respect to an initiator. Assertion indicates input to the initiator.This signal also distinguishes between
Selection and Reselection phases.
MSG (Message) - A signal driven by a target during the Message phase.
REQ (Request) - A signal driven by a target to indicate a request for REQ/ACK data transfer handshake.
ACK (Acknowledge) - A signal driven by an initiator to indicate an acknowledgment for a REQ/ACK data
transfer handshake.
ATN (Attention) - A signal driven by an initiator to indicate the Attention condition. It is used to request to
send a message out to the target. See paragraph 3.2.1. If an initiator asserts ATN while asserting SEL it
indicates to the target that the initiator supports messages other than command complete.
RST (Reset) - An “OR-tied”signal that indicates the Reset condition.

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DIFFSENS (Differential Sense) - When the drive has differential SCSI I/O circuits, the DIFFSENS signal
disables the drive’s differential driver/receiver circuits if the SCSI I/O cable is plugged in upside down, or if a
single-ended SCSI I/O cable is plugged into a differential I/O drive. Disabling the differential I/O drivers/
receiversisnecessary to prevent burning themoutif a groundedI/O lineis connected toanyofthe differential
circuit outputs, which are at a positive voltage (+2 V or +3 V) when not disabled.
DB(7-0,P) and DB(15-8,P1) (Data Bus) - Sixteen data bit signals, plus parity bit signals form a Data Bus.
DB(7) is the most significant bit and has the highest priority during the Arbitration phase (on both eight and
sixteen device systems). Bit number significance, and priority decrease downward to DB(0), and then from
DB15 down to DB8 (DB0 is higher than DB15).A data bit is defined as one when the signal is asserted and
is defined as zero when the signal is negated.
Data parity DB(P) and DB(P1) is odd -The use of parity is a system option.The disc drive always checks
parity on the data bits, but has the capability to enable/disable parity error reporting to the host. See configu-
ration selection in the applicable Product Manual.Parity checking is not valid during the Arbitration phase.
Greater detail on each of the SCSI Bus signals is found in the following sections.
2.1.1 Drive Select
For SCSI ID selection install drive select jumpers as shown in configuration selection figure in applicable
Product Manual. Refer to section 10 of the individual drive Product Manual for the location of the drive select
header.The disc drive using the eight bit data interface can have one of eight ID bits selected by installing 0
to 3 jumpers in a binary coded configuration on the drive select header.Drives using the 16 bit data interface
can have one of sixteen ID bits selected by installing 0 to 4 jumpers in a binary coded configuration on the
drive select header.
2.1.2 Signal Values
Signals may assume true or false values.There are two methods of driving these signals.In both cases, the
signal shall be actively driven true, or asserted. In the case of OR-tied drivers, the driver does not drive the
signal to the false state, rather the bias circuitry of the bus terminators pulls the signal false whenever it is
released by the drivers at every SCSI device. If any driver is asserted, then the signal is true. In the case of
non-OR-tieddrivers,the signal may benegated. Negated means thatthesignal may be activelydriven false,
or may be simply released (in which case the bias circuitry pulls it false), at the option of the implementor.
2.1.3 OR-Tied signals
The BSY and RST signals shall be OR-tied only. In the ordinary operation of the bus, these signals are
simultaneouslydriventrueby several drivers.No signals otherthan BSY, RST, and DB(P) aresimultaneously
driven by two or more drivers, and any signal other than BSY and RST may employ OR-tied or non-OR-tied
drivers. DB(P) shall not be driven false during the Arbitration phase. There is no operational problem in
mixing OR-tied and non-OR-tied drivers on signals other than BSY and RST.
2.1.4 Signal sources
Table 2.1.4-1 indicates which type of SCSI device is allowed to source each signal. All SCSI device drivers
that are not active sources shall be in the passive state. Note that the RST signal may be sourced by any
SCSI device at any time.The disc drive functions as a target.

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2.2 SCSI bus timing
Unlessotherwise indicated, thedelaytime measurementsforeach SCSI device,defined in Paragraphs2.2.1
through 2.2.14, shall be calculated from signal conditions existing at that SCSI device’s own SCSI bus con-
nection. Thus, these measurements (except skew delay) can be made without considering delays in the
cable.
See Section 2.3 for Fast Synchronous transfer option timing.
Table 2.1.4-1. Signal sources
Signals
C/D, I/O,
Bus Phase BSY SEL MSG, REQ ACK/ATN DB(7-0,P) (15-8,P1)
Bus Free None None None None None
Arbitration All Winner None None SCSI ID
Selection I&T Init. None Init. Init.
Reselection I&T Target Target Init. Target
Command Target None Target Init. Init.
Data In Target None Target Init. Target
Data Out Target None Target Init. Init.
Status Target None Target Init. Target
Message In Target None Target Init. Target
Message Out Target None Target Init. Init.
ALL: The signal shall be driven by all actively arbitrating SCSI devices.
SCSI ID: Aunique databit(theSCSI ID) shallbe drivenbyeach activelyarbitratingSCSI device:theother
seven data bits shall be released (i.e., not driven) by this SCSI device. The parity bit [DB(P),
DB(P1)] may be undriven or driven to the true state, but shall never be driven to the false state
during this phase.
I&T: The signal shall be driven by the initiator, target, or both, as specified in the Selection phase and
Reselection phase.
Init: If this signal is driven, it shall be driven only by the active initiator.
None: The signal shall be released;that is, not be driven by any SCSI device.The bias circuitry of the
bus terminators pulls the signal to the false state.
Winner: The signal shall be driven by the one SCSI device that wins arbitration.
Target: If the signal is driven, it shall be driven only by the active target.
2.2.1 Arbitration delay (2.4 us)
The minimum time a SCSI device shall wait from asserting BSY for arbitration until the Data Bus can be
examined to see if arbitration has been won.There is no maximum time.
2.2.2 Assertion period (90 ns)
The minimum time that a target shall assert REQ while using synchronous data transfers.Also, the minimum
time that an initiator shall assert ACK while using synchronous data transfers.

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2.2.3 Bus clear delay (800 ns)
The maximum time for a SCSI device to stop driving all bus signals after:
(1) The Bus Free phase is detected (BSY and SEL both negated for a bus settle delay).
(2) SEL is received from another SCSI device during the Arbitration phase.
(3) The transition of RST to assertion.
Note. Forthe first condition above,the maximum timefora SCSI deviceto clear thebusis 1200 ns
from BSY and SEL first becoming both negated. If a SCSI device requires more than a bus
settle delay to detect Bus Free phase, it shall clear the bus within a Bus Clear delay minus
the excess time.
2.2.4 Bus free delay (800 ns)
The minimum time that a SCSI device shall wait from its detection of the Bus Free phase (BSY and SEL both
negated for a bus settle delay) until its assertion of BSY when going to the Arbitration phase.
2.2.5 Bus set delay (1.8 µs)
The maximum time for a SCSI device to assert BSY and its SCSI ID bit on the Data Bus after it detects Bus
Free phase (BSY and SEL both negated for a bus settle delay) for the purpose of entering the Arbitration
phase.
2.2.6 Bus settle delay (400 ns)
The time to wait for the bus to settle after changing certain control signals as specified in the protocol defini-
tions.
2.2.7 Cable skew delay (10 ns)
The maximum difference in propagation time allowed between any two SCSI bus signals when measured
between any two SCSI devices.
2.2.8 Data release delay (400 ns)
The maximum time for an initiator to release the Data Bus signals following the transition of the I/O signal
from negation to assertion.
2.2.9 Deskew delay (45 ns)
The minimum time required for deskew of certain signals.
2.2.10 Disconnection delay (200 µs)
The minimum time that a target shall wait after releasing BSY before participating in an Arbitration phase
when honoring a Disconnect message from the initiator.
2.2.11 Hold time (45 ns)
Theminimum timeaddedbetween theassertionof REQ or ACKand the changingofthe data linesto provide
hold time in the initiator or target, respectively, while using synchronous data transfers.
2.2.12 Negation period (90 ns)
Theminimumtime that a targetshall negate REQwhileusing synchronous datatransfers.Also,the minimum
time that an initiator shall negate ACK while using synchronous data transfers.