Seagate ST31200, ST32430, ST15230, ST3655, ST11950 Product Manual

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Disc Drive SCSI-2/SCSI-3 Interface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Family Models:

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST11200, ST12400, ST12400 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST3600, ST3610,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST31200, ST31200 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32430, ST32430 Wide, ST15230,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST3655, ST11950, ST11950 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST12450 Wide, ST12550,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST12550 Wide, ST15150,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST15150 Wide, ST31250

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST31250 Wide, ST32550

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32151, ST31051

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32550 Wide, ST410800

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST34371

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Product Manual, Volume 2; Version 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Disc Drive SCSI-2/SCSI-3 Interface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Family Models:

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST11200, ST12400, ST12400 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST3600, ST3610,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST31200, ST31200 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32430, ST32430 Wide, ST15230,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST3655, ST11950, ST11950 Wide,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST12450 Wide, ST12550,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST12550 Wide, ST15150,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST15150 Wide, ST31250

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST31250 Wide, ST32550

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32151, ST31051

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST32550 Wide, ST410800

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ST34371

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Product Manual, Volume 2; Version 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 1995 Seagate Technology, Inc. All rights reserved

Publication Number: 77738479, Rev E
January 1995

Seagate, Seagate Technology and the Seagate logo are registered trademarks of Seagate Technology,
Inc. HA WKTM, SeaF AX, SeaFone , SeaTDD and SeaBOARD are trademarks of Seagate T echnology,

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 Seagate Technology, Inc.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E v
_____________________________________________________________________________________

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, 162­170, 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.

vi Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

T ab le 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-Tied signals ............................................................................................... 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 Selection Abort time ......................................................................................... 11

2.2.15 Selection Timeout delay ................................................................................... 1 1

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

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E vii
_____________________________________________________________________________________

T ab le 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 Contingent Allegiance 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 Command implementation requirements ...................................................................... 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 Untagged queuing............................................................................................68

4.7.2 T agged queuing ............................................................................................... 68

4.8 Parameter Rounding.....................................................................................................70

4.9 Command Processing considerations and exception conditions................................... 70

4.9.1 Programmable Operating definition..................................................................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.................................................................8 1

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

viii Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

T ab le 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 Device Types....................................................... 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 and Verify Error Counter pages

(code 02, 03, 05h) ......... 116

5.1.3.2.2 Non-Medium Error page ...............................(code 06h)11 8

5.1.3.2.3 Cache Statistics page ...................................(code 37h) 11 8

5.1.3.3 Log Sense command ....................................................(4Dh)....... 1 19

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 and Verify command ............................................(2Eh) ....... 176

5.2.2.6 V erify command ............................................................(2Fh) ....... 177

5.2.2.7 Synchronize Cache command ......................................(35h) ....... 178

5.2.2.8 Read Defect Data command.........................................(37h) ....... 179

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E ix
_____________________________________________________________________________________

T ab le 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 Seagate T echnical Support Service ..................................................................................... 187

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 1
_____________________________________________________________________________________

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: V olume 1 Pr oduct Manuals have tables in Section 11 that specify which SCSI-1 or SCSI-2/SCSI­3 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 imple­mentation of the SCSI interface.

This interface manual is not intended to be stand-alone text on SCSI-1 or SCSI-2/SCSI-3 features. Refer­ence must be made back to the individual drive Product Manuals to find out what are SCSI-1 and what are
SCSI-2/SCSI-3 features.

This specification is V olume 2 of a set of man uals that is made up of separate drive Product Manuals (V olume

1) and this manual. This V olume 2 Manual is referenced by other V olume 1 Product Manuals representing 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, ST12400 Wide, 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 Seagate Technology, Inc. subset of the SCSI (Small Computer Systems
Interface) as implemented on the Seagate built disc drives listed abov e . 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
_____________________________________________________________________________________

The Seagate SCSI interface described herein consists of a 9 or 18 bit bidirectional bus (8 data + 1 parity or 16
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 architec­ture of the target (logical block addressing is used), and some other miscellaneous features.

The SCSI physical interface uses either single ended driv ers and receivers or diff erential drivers and receiv­ers 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 dr ive
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 b us, 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
unique meanings.

Initiator - A SCSI device (usually a host system) that requests an operation to be perf ormed by another SCSI
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 - An I/O process consists of one initial connection and z ero or 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, ABORT TAG, 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”).

I T 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”).

I T L Q nexus - A nexus between an initiator , a Logical Unit, and a queue tag f ollowing the successful receipt
of one of the QUEUE messages. This relationship replaces the prior I T L ne xus . (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 encoded three bit identifier for the logical unit. The disc drive is considered Logical
Unit number zero.

LSB - Least significant byte MSB - Most significant byte ms - millisecond
LUN - Logical unit number mm - Millimetre

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 3
_____________________________________________________________________________________

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 ref erred 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 - The term used for bits, b ytes, fields, and code values that are set aside f or future standardization.
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 ref erring 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 allo wing the cable terminators to bias the signal to the false state (by placing the

driver in the high impedance condition).

xxh - Numbers followed by lo wer 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 v alues that are vendor specific.
Zero - A logical false signal v alue, (negation).

1.3 Physical interface characteristics

The physical interface characteristics (cables, connectors, electrical descriptions, termination requirements,
etc.) for the drives covered by this Interface Manual are found in each individual Product Manual, since these
features are not the same for all drives.

4 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

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

Change Definition 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) 1 A 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) 5 6 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
Ver ify 2F 0 dir. access 177
Write 0A 0 dir. access 134

Write and Verify 2E 1 dir. access 176
Write Extended 2A 1 dir. access 174
Write Long 3F 1 dir. access 182

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 5
_____________________________________________________________________________________

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
Abort T ag 0D 29

Bus Device Reset 0C 29
Clear Queue 0E 29

Command Complete 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
Queue T ag Messages 33

Head of Queue Tag 21 33
Ordered Queue Tag 22 34
Simple Queue Tag 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 1 1 34 (optional)
Wide Data Transf er Request 01 38 (extended meessage)

6 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

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 indi­vidual disc drive Product Manuals (V olume 1) Section “Interface requirements”, which covers all of the inter­face 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
SCSI bus. Some Seagate drives support systems with a maximum of sixteen SCSI devices on the SCSI bus.
Each SCSI device has a SCSI ID Bit assigned as shown in Figure 2.0-1. The SCSI ID is assigned by installing
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”.

When two SCSI devices communicate on the SCSI Bus one acts as an initiator and the other acts as a target.
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

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 7
_____________________________________________________________________________________

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 par ticular 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 ev ent m ust 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's Volume 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) - A signal driven b y a target to indicate whether Control or Data information is on the Data

Bus. Assertion (see Parag raph 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. Asser tion 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 dr iven 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 asser ting 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.

8 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

DIFFSENS (Differential Sense) - When the drive has differential SCSI I/O circuits, the DIFFSENS signal

disables the drive’ s diff erential driver/receiv er circuits if the SCSI I/O cab le 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/
receivers is necessary to prevent b urning them out if a grounded I/O line is connected to any of the 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 chec ks
parity on the data bits, but has the capability to enable/disable parity error reporting to the host. See configu­ration 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 hav e 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 interf ace
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 v alues. 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-tied drivers, the signal may be negated. Negated means that the signal may be actively driven 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
simultaneously driven true by se veral drivers. No signals other than BSY, RST , and DB(P) are simultaneously
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 dr iven 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.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 9
_____________________________________________________________________________________

2.2 SCSI bus timing

Unless otherwise indicated, the delay time measurements for each SCSI device, defined in Paragraphs 2.2.1
through 2.2.14, shall be calculated from signal conditions existing at that SCSI device’s own SCSI bus con­nection. 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 T arget None Target Init. Init.
Status Target None T arget Init. Target
Message In Target None Target Init. Target
Message Out T arget None Target Init. Init.

ALL: The signal shall be driven by all actively arbitrating SCSI devices.
SCSI ID: A unique data bit (the SCSI ID) shall be driven by each actively arbitrating SCSI device: the other

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.

10 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

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. For the first condition above, the maximum time for a SCSI device to clear the bus is 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 dela y) 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 defini­tions.

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)

The minimum time added between the assertion of REQ or ACK and the changing of the data lines to provide
hold time in the initiator or target, respectively, while using synchronous data transfers.

2.2.12 Negation period (90 ns)

The minimum time that a target shall negate REQ while using synchronous data transf ers. Also, the minimum
time that an initiator shall negate ACK while using synchronous data transfers .

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 11
_____________________________________________________________________________________

2.2.13 Reset hold time (25 µs)

The minimum time for which RST is asserted. There is no maximum time.

2.2.14 Selection abort time (200 µs)

The maximum time that a target (or initiator) shall take from its most recent detection of being selected (or
reselected) until asserting a BSY response. This timeout is required to ensure that a target (or initiator) does
not assert BSY after a Selection (or Reselection) phase has been aborted. This is not the selection timeout
period; see Sections 3.1.3.5 and 3.1.4.2 for a complete description.

2.2.15 Selection timeout delay (250 ms recommended)

The minimum time an initiator (or target) should wait for a BSY response during the Selection (or Reselection)
phase before starting the timeout procedure. The drive implements this 250 ms selection timeout delay.

2.2.16 Transfer period (negotiated by Synchronous Data Transfer message)

The minimum time allowed between the leading edges of successive REQ pulses and of successive ACK
pulses while using synchronous data transfers. (See Sections 3.1.5.2 and 3.5.3.2)

2.3 Fast synchronous transfer option

When devices negotiate a synchronous data transfer period of less than 200 ns they are said to be using “fast
synchronous data transfers”. Devices which negotiate a synchronous data transfer period greater than or
equal to 200 ns use timing parameters specified in 2.2. When a fast synchronous data transfer period is
negotiated, those specific times redefined in this section are used; those not redefined remain the same. The
minimum synchronous data transfer period is 100 ns.

2.3.1 Fast Assertion period (30 ns)

This value is the minimum time that a target shall assert REQ while using fast synchronous data transfers.
Also, the minimum time that an initiator shall assert ACK while using f ast synchronous data transf ers.

2.3.2 Fast cable skew delay (5 ns)

This value is the maximum difference in propagation time allowed between any two SCSI bus signals mea­sured between any two SCSI devices while using fast synchronous data transfers.

2.3.3 Fast deskew delay (20 ns)

This value is the minimum time required for deskew of certain signals while using fast synchronous data
transfers.

2.3.4 Fast hold time (10 ns)

This value is the minimum time added between the assertion of REQ or ACK and the changing of the data
lines to provide hold time in the initiator or target respectively, while using fast synchronous data transfers .

2.3.5 Fast negation period (30 ns)

This value is the minimum time that a target shall negate REQ while using fast synchronous data transfers.
Also, the minimum time that an initiator shall negate A CK while using fast synchronous data transfers.

12 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

3.0 Logical characteristics

The operations of the SCSI bus as described in Section 3 are supported by the disc drive, as specified in
each drive’s Product Man ual (Vol. 1). The disc drive always functions as the target unless otherwise stated.

3.1 SCSI bus phases

The disc drive responds to 8 distinct bus phases.
Bus Free phase

Arbitration phase
Selection phase
Reselection phase

Command Phase
Data (in and out)

These phases are collectively termed the Information transfer phases
Status (in only)
Message (in and out)

The SCSI Bus can never be in more than one phase at a time.

3.1.1 Bus free phase

The Bus Free phase indicates that no SCSI device is actively using the SCSI bus and it is available for
subsequent users. In some cases a target reverts to the Bus Free phase to indicate an error condition that it
has no other way to handle. This is called an unexpected disconnect.

SCSI devices shall detect the Bus F ree phase after SEL and BSY are both false f or at least a bus settle delay.
SCSI devices shall release all SCSI bus signals within a bus clear delay after BSY and SEL are continuously

negated for a bus settle dela y. If a SCSI de vice requires more than a b us settle delay to detect the Bus Free
phase, it shall release all SCSI bus signals within a bus clear delay minus the excess time to detect the Bus
Free phase. The total time to clear the SCSI bus shall not exceed a bus settle delay plus a bus clear delay.

Initiators normally do not expect BUS FREE phase to begin because of the target's release of the BSY signal
except after one of the following occurrences:

(1) after a reset condition is detected.
(2) after an ABORT message is sucessfully received by a target.
(3) after a BUS DEVICE RESET message is successfully received by a target.
(4) after a DISCONNECT message is successfully transmitted from a target (see 3.5.3.1).
(5) after a COMMAND COMPLETE message is successfully transmitted from a target (see 3.5.3.1).
(6) after a RELEASE RECOVER Y message is successfully received by a target.
(7) after an ABORT TAG message is successfully received by a target.
(8) after a CLEAR QUEUE message is successfully received by a target.

The BUS FREE phase may also be entered after an unsuccessful selection or reselection, although in this
case it is the release of the SEL signal rather than the release of the BSY signal that first establishes the BUS
FREE phase.

If an initiator detects the release of the BSY signal by the target at any other time, the target is indicating an
error condition to the initiator. The target may perform this transition to the BUS FREE phase independent of
the state of the A TN signal. The initiator shall manage this condition as an unsuccessful I/O process termina­tion. The target terminates the I/O process by clearing all pending data and status information for the aff ected
logical unit or target routine. The target may optionally prepare sense data that may be retr ieved by a RE­QUEST SENSE command. When an initiator detects an unexpected disconnect, it is recommended that a
REQUEST SENSE command be attempted to obtain any valid sense data that may be available.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 13
_____________________________________________________________________________________

3.1.2 Arbitration phase

The Arbitration phase allows one SCSI device to gain control of the SCSI b us so that it can assume the role
of an initiator or target. The disc drive arbitrates for the bus as a target implementing reselection or when
performing AEN (if AEN is implemented). The disc drive supports arbitration by multiple SCSI devices .

The procedure for a SCSI device to obtain control of the SCSI bus is as follows:

1. The SCSI device shall first wait for the Bus Free phase to occur. The Bus Free phase is detected when

BSY and SEL are simultaneously and continuously negated for a minimum of a bus settle delay.
(Implementors note: This bus settle delay is necessary because a transmission line phenomenon kno wn
as a “Wire-OR glitch” may cause BSY to briefly appear negated, even though it is being asserted.)

2. The SCSI device shall wait a minimum of a bus free delay after detection of the Bus Free phase (i.e. after

BSY and SEL are both negated for a bus settle delay) before driving any signal.

3. Following the bus free delay in Step (2), the SCSI device may arbitrate for the SCSI bus by asserting both

BSY and its own SCSI ID, however the SCSI device shall not arbitrate (i.e. assert BSY and its SCSI ID)
if more than a bus settle delay has passed since the Bus Free phase was last observed. (Implementors
Note: There is no maxim um delay bef ore asserting BSY and the SCSI ID following the b us free dela y in
Step (2) as long as the bus remains in the Bus Free phase. However, SCSI devices that delay longer
than a bus settle delay plus a bus set delay from the time when BSY and SEL are first negated may fail
to participate in arbitration when competing with faster SCSI devices.)

4. After waiting at least an arbitration delay (measured from its assertion of BSY) the SCSI device shall

examine the Data Bus. If a higher priority SCSI ID bit is true on the Data Bus [DB(7) is the highest], the
SCSI device has lost the arbitration and the SCSI device must release its signals and return to Step (1).
If no higher priority SCSI ID bit is true on the Data Bus, the SCSI device has won the arbitration and it
shall assert SEL. Any other SCSI de vice that is participating in the Arbitration phase has lost the arbitra­tion and shall release BSY and its SCSI ID bit within a bus clear delay after SEL becomes true. A SCSI
device that loses arbitration may return to Step (1).

5. The SCSI device that wins arbitration shall wait at least a bus clear delay plus a bus settle delay after

asserting SEL before changing any signals.

Note. The SCSI ID bit is a single bit on the Data Bus that corresponds to the SCSI device’s

unique SCSI address. All other seven Data Bus bits shall be released by the SCSI device.
Parity is not valid during the Arbitration phase, DB(P) may be undriven or driven to the
true state, but shall not be driven to the false state.

3.1.3 Selection phase

The Selection phase allows an initiator to select a target for the purpose of initiating some target function
(e.g., Read or Write command).

Note. During the Selection phase the I/O signal shall be negated so this phase can be distinguished from

the Reselection phase.

14 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

3.1.3.1 Nonarbitrating system

In systems with the Arbitration phase not implemented, the initiator shall first detect the Bus Free phase and
then wait a minimum of a bus clear dela y. Then, except in certain single initiator environments with initiators
employing the single initiator option (see 3.1.3.4), the initiator shall assert the desired target’s SCSI ID and its
own initiator SCSI ID on the Data Bus. After two deskew delays, the initiator shall assert SEL.

3.1.3.2 Arbitrating systems

In systems with the Arbitration phase implemented, the SCSI device that won the arbitration has both BSY
and SEL asserted and has delayed at least a bus clear delay plus a bus settle delay before ending the
Arbitration phase. The SCSI device that won the arbitration becomes an initiator by releasing I/O. Except in
certain single initiator environments with initiators employing the single initiator option (see 3.1.3.4), the
initiator shall set the Data Bus to a value which is the OR of its SCSI ID bit and the target’ s SCSI ID bit. The
initiator shall then wait at least two deskew dela ys and release BSY. The initiator shall then w ait at least a bus
settle delay before looking for a response from the target.

3.1.3.3 All systems

In all systems, the target shall determine that it is selected when SEL and its SCSI ID bit are true and the BSY
and I/O signals are false for at least a b us settle delay. The selected target will e xamine the Data Bus in order
to determine the SCSI ID of the selecting initiator unless the initiator employed the single initiator option (see

3.1.3.4). The selected target shall then asser t BSY within a selection abor t time of its selection; this is re­quired for correct operation of the timeout procedure. In systems with parity implemented, the target shall not
respond to a selection if bad parity is detected. Also , if more than two SCSI ID bits are on the Data Bus , the
target shall not respond to selection. At least tw o deskew dela ys after the initiator detects BSY is asserted, it
shall release SEL and may change the Data Bus.

3.1.3.4 Single initiator option

Initiators that do not implement the Reselection phase, and do not operate in the multiple initiator environ­ment, are allowed to set only the target’ s SCSI ID bit during the Selection phase. This mak es it impossible for
the target to determine the initiator’s SCSI ID.

3.1.3.5 Selection time out procedure

A Selection timeout procedure is specified for clearing the SCSI bus. If the initiator waits a minimum of a
selection timeout delay and there has been no BSY response from the target, the initiator shall continue
asserting SEL and shall release the Data Bus. If the initiator has not detected BSY to be asserted after at
least a selection abort time plus two deskew delays, the initiator shall release SEL allowing the SCSI bus to
go to the Bus Free phase. SCSI devices shall ensure when responding to selection that the selection was still
valid within a selection abort time of their assertion of BSY. Failure to comply with this requirement could
result in an improper selection (two targets connected to the same initiator, wrong target connected to an
initiator, or a target connected to no initiator).

The disc drive supports systems that implement this procedure.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 15
_____________________________________________________________________________________

3.1.4 Reselection phase

Reselection is a phase that allows a target to reconnect to an initiator for the purpose of continuing some
operation that was previously started by the initiator but was suspended by the target (i.e., the target discon­nected by allowing a Bus Free phase to occur before the operation was complete).

Reselection can be used only in systems that have Arbitration phase implemented.
The disc drive implements the Reselection phase if the system is capable of supporting Reselection.
ATN during Selection implies that the host supports messages other than command complete.

Bit 6 of the Identify message indicates that the Disconnected/Reconnect privilege is granted.
A TN not asserted during Selection means that the host doesn’t support the Identify message, so the Discon-

nected/Reconnect privilege cannot be granted. If a target is not granted disconnect/reconnect privileges, it
shall not disconnect until the current command is completed. None of the Disconnect/Reconnect Control
Page (page 02h) parameters of Mode Select are applicable if disconnect/reconnect privileges are not granted
by the initiator . Operations taking longer than the bus inactivity limit specified do not cause a disconnect.

3.1.4.1 Reselection Procedure

Upon completing the Arbitration phase, the winning SCSI device has both BSY and SEL asserted and has
delayed at least a bus clear delay plus a bus settle delay. The winning SCSI device becomes a target by
asserting the I/O signal. That device shall also set the Data Bus to a value that is the OR of its SCSI ID bit and
the initiator’s SCSI ID bit. The target shall wait at least two deske w dela ys and release BSY. The target shall
then wait at least a bus settle delay before looking for a response from the initiator.

The initiator shall determine that it is reselected when SEL, I/O, and its SCSI ID bit are true and BSY is false
for at least a bus settle dela y. The reselected initiator may e xamine the Data Bus to determine the SCSI ID of
the reselecting target.

The reselected initiator shall then assert BSY within a selection abort time of its most recent detection of
being reselected; this is required for correct operation of the timeout procedure. In systems with parity imple­mented, the initiator shall not respond to Reselection if bad parity is detected. The initiator shall not respond
to a Reselection if more than two SCSI ID bits are on the Data Bus.

After the target detects BSY, it shall also assert BSY and wait at least two deskew delays and then release
SEL. The target may then change the I/O signal and the Data Bus. After the reselected initiator detects SEL
false, it shall release BSY. The target shall continue asserting BSY until the target is ready to relinquish the
SCSI bus.

Note. When the target is asserting BSY, a transmission line phenomenon known as a “Wired-OR

glitch” may cause BSY to appear false for up to a round trip propagation delay following the
release of BSY by the initiator . This is the reason wh y the Bus F ree phase is recognized only
after both BSY and SEL are continuously false for a minim um of a bus settle delay. Cables
longer than 25 metres should not be used even if the chosen driver, receiver, and cable
provide adequate noise margins, because they increase the duration of the glitch and could
cause SCSI devices to inadvertently detect the Bus Free phase.

16 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

3.1.4.2 Reselection timeout procedure

This Reselection timeout procedure is specified for clearing the SCSI bus during a Reselection phase. If the
target waits a minimum of a selection timeout period and there has been no BSY response from the initiator,
the target shall continue asserting SEL and I/O and shall release all Data Bus signals. If the target has not
detected BSY to be true after at least a selection abort time plus two deskew delays, the target shall release
SEL and I/O allowing the SCSI bus to go to the Bus Free phase. SCSI devices that respond to Reselection
shall ensure that the Reselection was still valid within a selection abort time of their assertion of BSY . F ailure
to comply with this requirement could result in an improper Reselection (two initiators connected to the same
target or the wrong initiator connected to a target).

If an initiator times out while waiting to be reselected, the initiator should attempt to select and issue Request
Sense to determine if the previous command is:

1. Still in process (Busy Status is returned),

2. Aborted with valid Request Sense data, or

3. Aborted without valid Request Sense data.

3.1.5 Information transfer phases

NOTE: The Command, Data, Status, and Message phases are grouped together as information transfer
phases because they are all used to transfer data or control information via the Data Bus. The actual con­tents of the information is beyond the scope of this section.

The C/D, I/O, and MSG signals are used to distinguish between the different information transfer phases.
(See T able 3.1.5-1). The target drives these three signals and theref ore controls all changes from one phase
to another. The initiator can request a Message Out phase by asserting ATN, while the target can cause the
Bus Free phase by releasing MSG, C/D, I/O, and BSY.

Table 3.1.5-1. Information transfer phases

Signal

MSG C/D I/O Phase Name Direction of Transfer Comment

000DATA OUT Initiator to target Data
001DATA IN Initiator from target Phase
010COMMAND Initiator to target
011STATUS Initiator from target
100*
101*
1 1 0 MESSAGE OUT Initiator to Target Message

1 1 1 MESSAGE IN Initiator from Target Phase
Key: 0 = False, 1 = Tr ue, * = Reserved
The information transfer phases use one or more REQ/ACK handshak es to control the information transfer.

Each REQ/ACK handshake allows the transfer of one byte of information. During the information transfer
phases BSY shall remain true and SEL shall remain false. Additionally , during the inf ormation transfer phases,
the target shall continuously envelope the REQ/ACK handshake(s) with C/D, I/O, and MSG in such a manner
that these control signals are valid for a bus settle delay before the assertion of REQ of the first handshake
and remain valid until the negation of ACK at the end of the last handshak e.

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 17
_____________________________________________________________________________________

3.1.5.1 Asynchronous information transfer

The target shall control the direction of information transfer by means of the I/O signal. When I/O is true,
information shall be transferred from the target to the initiator. When I/O is false, information shall be trans­ferred from the initiator to the target.

If I/O is true (transfer to the initiator), the target shall first drive DB(7-0,P)* to their desired values, delay at
least one deskew delay plus a cab le skew dela y, then assert REQ. DB(7-0,P)* shall remain valid until ACK is
true at the target. The initiator shall read DB(7-0,P)* after REQ is true, then signal its acceptance of the data
by asserting ACK. When A CK becomes true at the target, the target may change or release DB(7-0, P)* and
shall negate REQ. After REQ is false the initiator shall negate ACK. After ACK is false, the target may con­tinue the transfer by driving DB(7-0,P)* and asserting REQ, as described above.

If I/O is false (transfer to the target) the target shall request information by asserting REQ. The initiator shall
drive DB(7-0,P)* to their desired values, delay at least one deskew delay plus a cable skew delay and assert
ACK. The initiator shall continue to drive the DB(7-0,P)* until REQ is false. When ACK becomes true at the
target, the target shall read DB(7-0,P)*, then negate REQ. When REQ becomes false at the initiator, the
initiator may change or release DB(7-0,P)* and shall negate ACK. The target may continue the transfer by
asserting REQ, as described above.

3.1.5.2 Synchronous data transfer

Synchronous data transfer may be used only in the data phase if previously agreed to by the initiator and
target through the message system (see SYNCHRONOUS D A TA TRANSFER REQUEST message 3.5.3.2).
The messages determine the use of synchronous mode by both SCSI devices and establish a REQ/ACK
offset and a transfer period.

The REQ/ACK offset specifies the maximum number of REQ pulses that can be sent by the target in advance
of the number of ACK pulses received from the initiator, establishing a pacing mechanism. If the number of
REQ pulses exceeds the number of A CK pulses by the REQ/ACK offset, the target shall not assert REQ until
the next ACK pulse is receiv ed. A requirement for successful completion of the data phase is that the number
of ACK and REQ pulses be equal.

The target shall assert the REQ signal for a minimum of an assertion period. The target shall wait at least the
greater of a transfer period from the last transition of REQ to true or a minimum of a negation period from the
last transition of REQ to false before asserting the REQ signal.

The initiator shall send one pulse on the ACK signal for each REQ pulse received. The ACK signal may be
asserted as soon as the leading edge of the corresponding REQ pulse has been received. The initiator shall
assert the ACK signal for a minimum of an assertion period. The initiator shall wait at least the greater of a
transfer period from the last transition of ACK to true or for a minimum of a negation period from the last
transition of ACK to false bef ore asserting the ACK signal.

__________
*And where applicable, DB(15-8, P1).

18 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

If I/O is asserted (transfer to the initiator), the target shall first drive DB(7-0,P)* to their desired values, wait at
least one deskew delay plus one cable skew delay, then assert REQ. DB(7-0,P)* shall be held valid for a
minimum of one deskew dela y plus one cable ske w dela y plus one hold time after the assertion of REQ. The
target shall assert REQ for a minimum of an assertion period. The target ma y then negate REQ and change
or release DB(7-0,P)*. The initiator shall read the v alue on DB(7-0,P)* within one hold time of the transition of
REQ to true. The initiator shall then respond with an ACK pulse.

If I/O is negated (transfer to the target), the initiator shall transfer one b yte for each REQ pulse receiv ed. After
receiving a REQ pulse, the initiator shall first drive DB(7-0,P)* to their desired values, delay at least one
deskew dela y plus one cable ske w delay , then assert ACK. The initiator shall hold DB(7-0,P)* valid f or at least
one deskew dela y plus one cable skew dela y plus one hold time after the assertion of ACK. The initiator shall
assert ACK for a minimum of an assertion period. The initiator may then negate ACK and may change or
release DB(7-0,P)*. The target shall read the value of DB(7-0,P)* within one hold time of the tr ansition of ACK
to true.

3.1.6 Command phase

The Command phase allows the target to request command information from the initiator.
The target shall assert the C/D signal and negate the I/O and MSG signals during the REQ/ACK handshake(s)

of this phase.

3.1.7 Data phase

The Data phase is a term that encompasses both the Data In phase and the Data Out phase.

3.1.7.1 Data in phase

The Data In phase allows the target to request that it send data to the initiator.
The target shall assert the I/O signal and negate the C/D and MSG signals during the REQ/ACK handshake(s)

of this phase.

3.1.7.2 Data out phase

The Data Out phase allows the target to request that data be sent to it from the initiator.
The target shall negate the C/D, I/O, and MSG signals during the REQ/ACK handshake(s) of this phase.

3.1.8 Status phase

The Status phase allows the target to request that it send status information to the initiator.
See section 4.3 for details.
The target shall assert C/D and I/O and negate the MSG signal during the REQ/ACK handshake of this

phase.

__________
*And where applicable, DB(15-8, P1).

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 19
_____________________________________________________________________________________

3.1.9 Message phase

The Message phase is a term that references either a Message In or a Message Out phase. Multiple mes­sages may be sent during either phase. Multiple byte messages shall be wholly contained with a single
message phase. Messages supported by a particular disc drive are listed in the Product Manual for that
drive.

3.1.9.1 Message in phase

The Message In phase allows the target to request that it send message(s) to the initiator.
The target shall assert C/D, I/O, and MSG during the REQ/ACK handshake(s) of this phase.

3.1.9.2 Message out phase

The Message Out phase allows the target to request that message(s) be sent from the initiator to the target.
The target may inv oke this phase at its conv enience in response to the Attention condition (see 3.2.1) created
by the initiator.

The target shall assert C/D and MSG and negate I/O during the REQ/ACK handshake(s) of this phase. The
target shall handshake byte(s) in this phase until ATN goes false, unless an error occurs (see Message
Reject, 3.5.2).

If the target detects one or more parity error(s) on the message byte(s) received, it may indicate its desire to
retry the message(s) by asserting REQ after detecting A TN has gone false and bef ore changing to any other
phase. The initiator, upon detecting this condition, shall resend all of the previous message byte(s) sent
during this phase. When resending more than one message byte, the initiator shall assert ATN before assert­ing ACK on the first byte and shall maintain ATN asserted until the last byte is sent as described in 3.2.1.

If the target receives all of the message byte(s) successfully (i.e., no parity errors), it shall indicate that it shall
not retry by changing to any information transfer phase other than the Message Out phase and transfer at
least one byte. The target ma y also indicate that it has successfully received the message b yte(s) by chang­ing to the Bus Free phase (e.g., Abort or Bus Device Reset messages).

3.1.10 Signal restrictions between phases

When the SCSI bus is between two information transfer phases, the following restrictions shall apply to the
SCSI bus signals:

1. The BSY, SEL, REQ, and ACK signals shall not change.

2. The C/D, I/O, MSG, and Data Bus signals may change. When switching the Data Bus direction from Out

(initiator driving) to In (target driving), the target shall delay driving the Data Bus by at least a data release

delay plus settle delay after asserting the I/O signal and the initiator shall release the Data Bus no later

than a data release delay after the transition of the I/O signal to true. When switching the Data Bus

direction from In (target driving) to Out (initiator driving), the target shall release the Data Bus no later

than a deskew delay after negating the I/O signal.

3. The ATN and RST signals may change as defined under the descriptions for the Attention condition

(3.2.1) and Reset condition (3.2.2).

20 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
_____________________________________________________________________________________

3.2 SCSI bus conditions

The SCSI bus has three asynchronous conditions; the Attention condition, the Reset condition and the Con­tingent Allegiance condition. These conditions cause the SCSI device to perf orm certain actions and can alter
the phase sequence.

3.2.1 Attention condition

The Attention condition allows an initiator to inform a target that the initiator has a message ready. The target
gets this message at its convenience by performing a Message Out phase.

The initiator creates the Attention condition by asserting A TN at any time e xcept during the Arbitration or Bus
Free.

The initiator shall assert the A TN signal tw o deskew delays before negating the ACK signal for the last byte
transferred in a bus phase for the attention condition to be honored before transition to a new bus phase.
Asserting the ATN signal later might not be honored until a later bus phase and then may not result in the
expected action. The initiator shall negate the A TN signal tw o deskew dela ys before asserting the ACK signal
while transferring the last byte of the message. If the target detects that the initiator failed to meet this
requirement, then the target shall go to BUS FREE phase (see unexpected BUS FREE, 3.1.1).

The disc drive responds with MESSAGE OUT phase as follows:

1. If ATN occurs during a Data phase, Message Out occurs at a convenient time. It may not occur until

several logical b locks after ATN is first asserted.

2. If A TN occurs during a Command phase, Message Out occurs after tr ansf er of all Command Descriptor

Block bytes has been completed.

3. If A TN occurs during a Status phase, Message Out occurs after the status b yte has been ackno wledged

by the initiator.

4. If ATN occurs during a Message In Phase, Message Out occurs after the last byte of the current mes-

sage has been acknowledged by the initiator .

5. If ATN occurs during a Selection or Reselection phase, Message Out occurs immediately after that

Selection or Reselection phase. In the Reselection case, the disc drive enters the Message Out phase

after it has sent its Identify message for that Reselection Phase.
The initiator shall keep ATN asserted if more than one byte is to be transferred. The initiator may negate the

A TN signal at an y time except while the ACK signal is asserted during a Message Out phase. Recommended
practice is that the initiator negates ATN while REQ is true and ACK is false during the last REQ/ACK hand­shake of the Message Out phase.