Quantum DAT 24 User's Guide
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DDS-4 and DAT 72 Tape Drives and
Autoloaders
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SCSI Interface Manual
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Copyright © 2003 Certance LLC. All rights reserved
Part Number 50000697
June 2003, Rev.B
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information in this manual.
Contents Page iii
Contents
Introduction 1
Overview......................................................................................................................1
Drive Models ...............................................................................................................1
About This Manual ......................................................................................................1
SCSI Interface Description 2
Overview......................................................................................................................2
ANSI SCSI Bus Standards ...................................................................................2
Cabling and Connectors.......................................................................................2
Signal Descriptions......................................................................................................3
Command Set Description ..........................................................................................4
ANSI X3.131, 199x Conformance Statement (SCSI-2) ..............................................5
General features...................................................................................................5
Interface standards conformance.........................................................................5
Commands............................................................................................................6
* Autoloader only commands................................................................................6
Messages..............................................................................................................6
Vendor-unique commands....................................................................................6
SCSI Bus Protocol.......................................................................................................6
Waiting and Control Phases........................................................................................7
Arbitrating Systems...............................................................................................7
Selection and Reselection Phases..............................................................................9
Select With Attention ..........................................................................................10
Identify Message.................................................................................................10
Information Transfer Phases.....................................................................................11
Asynchronous Data Transfer..............................................................................11
Synchronous Data Transfer................................................................................13
Command Phase.......................................................................................................14
Data Phase................................................................................................................15
Data-In Phase.....................................................................................................15
Data-Out Phase..................................................................................................15
Status Phase.............................................................................................................15
Message Phase.........................................................................................................15
Message-In Phase..............................................................................................15
Page iv DDS-4 SCSI Interface Manual, Rev. B
Message-Out Phase...........................................................................................15
Command Descriptor Block.......................................................................................16
Logical Unit Support..................................................................................................17
SCSI Message Descriptions and Definitions.............................................................18
SCSI Status Code Descriptions and Definitions .......................................................23
Attention Condition....................................................................................................24
Reset Condition.........................................................................................................24
Unit Attention Condition.............................................................................................24
Buffered Mode...........................................................................................................25
Immediate Function...................................................................................................25
Residual Length Function..........................................................................................25
Disconnect/Reconnect Function................................................................................26
SCSI Memory Address Pointers................................................................................27
Current Data Pointers .........................................................................................27
Saved Data Pointers...........................................................................................27
Early Warning Function.............................................................................................27
Error Reporting..........................................................................................................28
Soft Errors...........................................................................................................28
Hard Errors..........................................................................................................28
Variable and Fixed Mode Recording.........................................................................28
Autoloader Operation ................................................................................................29
General SCSI Information...................................................................................29
SCSI Medium Changer Commands ...................................................................29
General Operation ..............................................................................................31
Loading and Initialization ....................................................................................31
Front Panel Operation.........................................................................................32
Cassette Selection..............................................................................................32
Automatic Loading Mode....................................................................................32
Magazine Ejection...............................................................................................33
Stray Tape Recovery..........................................................................................33
Commands 34
Introduction................................................................................................................34
Command Reference List...................................................................................34
Conventions........................................................................................................35
Command Descriptor Blocks (CDBs)........................................................................35
Command Descriptor Block Formats..................................................................35
Command Descriptor Block Field Descriptions..................................................36
Flag and Link Bit Descriptions ............................................................................36
ERASE (19h).............................................................................................................37
Contents Page v
ERASE Command Descriptor Block...................................................................37
Command Descriptor Block Field Description....................................................37
Completion Status ..............................................................................................37
EXCHANGE MEDIUM (AutoLoader Only) (A6h)......................................................39
EXCHANGE MEDIUM Command Descriptor Block...........................................39
Command Descriptor Block Field Descriptions..................................................39
Completion Status ..............................................................................................40
INITIALIZE ELEMENT STATUS (AutoLoader Only) (07h).......................................41
INITIALIZE ELEMENT STATUS Command Descriptor Block............................41
Completion Status ..............................................................................................41
INQUIRY (12h)..........................................................................................................42
INQUIRY Command Descriptor Block................................................................42
Command Descriptor Block Field Description....................................................42
Standard INQUIRY Data Format........................................................................43
Standard INQUIRY Data Format Field Descriptions..........................................43
INQUIRY Drive Serial Number Data Format Page.............................................45
Drive Serial Number Data Format Field Descriptions ........................................45
Completion Status ..............................................................................................45
LOAD/UNLOAD (1Bh)...............................................................................................46
LOAD/UNLOAD Command Descriptor Block.....................................................46
Command Descriptor Block Field Description....................................................46
Completion Status ..............................................................................................47
LOCATE (2Bh)..........................................................................................................48
LOCATE Command Descriptor Block ................................................................48
Command Descriptor Block Field Description....................................................48
LOCATE and the BT Bit......................................................................................49
Completion Status ..............................................................................................50
LOG SELECT (4Ch)..................................................................................................51
LOG SELECT Command Descriptor Block........................................................51
Command Descriptor Block Field Description....................................................52
Errors Detected in the Command Descriptor Block............................................52
Use of the PC Bits...............................................................................................52
LOG SELECT Parameter Data...........................................................................53
LOG SENSE (4Dh)....................................................................................................58
LOG SENSE Command Descriptor Block..........................................................58
Command Descriptor Block Field Description....................................................59
Using Page Control Bits......................................................................................60
Using the Parameter Pointer Field .....................................................................61
Log Sense Pages ...............................................................................................61
Completion Status ..............................................................................................73
Page vi DDS-4 SCSI Interface Manual, Rev. B
MODE SELECT (15h) ...............................................................................................75
MODE SELECT Command Descriptor Block.....................................................75
Command Descriptor Block Field Description....................................................76
MODE SELECT Parameters...............................................................................76
Parameter List Header Field Descriptions..........................................................77
Parameter List—Block Descriptor.......................................................................77
Parameter List—Block Descriptor Field Descriptions.........................................78
Mode Page Format .............................................................................................78
Completion Status...............................................................................................90
MODE SENSE (1Ah).................................................................................................91
MODE SENSE Command Descriptor Block.......................................................91
Command Descriptor Block Field Description....................................................92
MODE SENSE Parameters ................................................................................93
Parameter List Header Field Descriptions..........................................................93
Parameter List—Block Descriptor.......................................................................94
Parameter List Block Descriptor Field Descriptions ...........................................94
Mode Page Format .............................................................................................95
Completion Status.............................................................................................103
MOVE MEDIUM (Autoloader only) (A5h)................................................................104
MOVE MEDIUM Command Descriptor Block...................................................104
Completion Status.............................................................................................105
PREVENT/ALLOW MEDIA REMOVAL (1Eh).........................................................106
PREVENT/ALLOW MEDIA REMOVAL Command Descriptor Block...............106
Command Descriptor Block Field Description..................................................106
Completion Status.............................................................................................106
READ (08h) .............................................................................................................107
READ Command Descriptor Block...................................................................107
Command Descriptor Block Field Description..................................................107
Description of the READ Command .................................................................108
Completion Status.............................................................................................111
READ BLOCK LIMITS (05h) ...................................................................................112
READ BLOCK LIMITS Command Descriptor Block.........................................112
Command Descriptor Block Field Description..................................................112
Block Size Definition .........................................................................................112
Completion Status.............................................................................................113
READ DATA BUFFER (3Ch) ..................................................................................114
READ DATA BUFFER Command Descriptor Block.........................................114
Command Descriptor Block Field Description..................................................114
READ DATA BUFFER Header.........................................................................115
READ DATA BUFFER Header Field Descriptions ...........................................115
Contents Page vii
Completion Status ............................................................................................115
READ ELEMENT STATUS (Autoloader Only) (B8h)..............................................116
READ ELEMENT STATUS Command Descriptor Block .................................116
Element Status Data.........................................................................................116
Element Status Data Header............................................................................117
Completion Status ............................................................................................120
READ POSITION (34h)...........................................................................................121
READ POSITION Command Descriptor Block ................................................121
READ POSITION Command Descriptor Block Field Descriptions...................121
READ POSITION Data Format.........................................................................122
READ POSITION Data Format Field Descriptions...........................................122
READ POSITION Data Format.........................................................................123
READ POSITION Data Format Field Descriptions...........................................123
Completion Status ............................................................................................125
RECEIVE DIAGNOSTIC RESULTS (1Ch) .............................................................126
RECEIVE DIAGNOSTIC RESULTS Command Descriptor Block....................126
Command Descriptor Block Field Description..................................................126
Completion Status ............................................................................................127
RELEASE UNIT (17h / 57h)....................................................................................129
RELEASE UNIT Command Descriptor Block...................................................129
Command Descriptor Block Field Description..................................................130
Completion Status ............................................................................................130
REPORT DENSITY SUPPORT (44h).....................................................................131
REPORT DENSITY SUPPORT Command Descriptor Block...........................131
Command Descriptor Block Field Description..................................................131
REPORT DENSITY Response Data................................................................131
REPORT DENSITY SUPPORT Header...........................................................132
REPORT DENSITY SUPPORT Data block descriptor.....................................132
DENSITY SUPPORT Data Block Descriptor Field Descriptions......................132
Completion Status ............................................................................................133
REQUEST BLOCK ADDRESS (02h)......................................................................134
REQUEST BLOCK ADDRESS Command Descriptor Block............................134
Command Descriptor Block Field Description..................................................134
REQUEST BLOCK ADDRESS Address Data Format.....................................134
REQUEST BLOCK ADDRESS Address Data Field Description......................135
Completion Status ............................................................................................135
REQUEST SENSE (03h) ........................................................................................136
REQUEST SENSE Command Descriptor Block..............................................136
Sense Data Format...........................................................................................136
Sense Data Field Descriptions .........................................................................137
Page viii DDS-4 SCSI Interface Manual, Rev. B
Definition of Sense Keys...................................................................................138
Additional Sense Code and Code Qualifier......................................................138
Vendor-Specific Code Qualifiers.......................................................................143
Completion Status.............................................................................................148
RESERVE UNIT (16h / 56h)....................................................................................149
RESERVE UNIT Command Descriptor Block ..................................................149
Command Descriptor Block Field Description..................................................150
Completion Status.............................................................................................151
REWIND (01h).........................................................................................................152
REWIND Command Descriptor Block ..............................................................152
Command Descriptor Block Field Description..................................................152
Completion Status.............................................................................................152
SEEK BLOCK (0Ch)................................................................................................154
SEEK BLOCK Command Descriptor Block......................................................154
Command Descriptor Block Field Description..................................................154
Completion Status.............................................................................................155
SEND DIAGNOSTIC (1Dh).....................................................................................156
SEND DIAGNOSTIC Command Descriptor Block ...........................................156
Completion Status.............................................................................................157
SPACE (11h)...........................................................................................................158
SPACE Command Descriptor Block.................................................................158
Command Descriptor Block Field Descriptions................................................159
Space-by-Count Functions ...............................................................................159
Space by Position Functions.............................................................................160
Space and the RSMK Bit..................................................................................160
Completion Status.............................................................................................161
TEST UNIT READY (00h).......................................................................................162
TEST UNIT READY Command Descriptor Block.............................................162
TEST UNIT READY Detailed Operation...........................................................162
Completion Status.............................................................................................163
VERIFY (13h) ..........................................................................................................164
VERIFY Command Descriptor Block................................................................164
Command Descriptor Block Field Description..................................................164
Data Blocks Verified..........................................................................................164
Completion Status.............................................................................................165
WRITE (0Ah) ...........................................................................................................166
WRITE Command Descriptor Block .................................................................166
Command Descriptor Block field description....................................................166
Completion Status.............................................................................................166
WRITE DATA BUFFER (3Bh).................................................................................168
Contents Page ix
WRITE DATA BUFFER Command Descriptor Block.......................................168
Command Descriptor Block Field Descriptions................................................169
WRITE DATA BUFFER Data Header...............................................................169
Completion Status ............................................................................................170
WRITE FILEMARKS (10h)......................................................................................171
WRITE FILEMARKS Command Descriptor Block............................................171
Command Descriptor Block Field Description..................................................171
Completion Status ............................................................................................172
Introduction Page 1
Introduction
1
Overview
The Seagate DDS-4 and DAT 72 DAT drives are designed for computer
environments requiring high performance, high capacity data storage. These drives
are available in 3.5-inch or 5.25-inch internal configurations or as an external
subsystem. The Autoloaders contain a DDS-4 or DAT 72 drive with an enclosure
and tape manipulation mechanism.
Seagate DDS-4 and DAT 72 drives contain an embedded Small Computer Systems
Interface (SCSI) controller. These drives provide synchronous or asynchronous
SCSI and a high speed burst synchronous data transfer rate of 80 Mbytes/second.
The internal drive form factors are tailored for easy installation in today's computers
and the full-featured embedded SCSI controller facilitates easy integration into a
variety of systems.
Drive Models
This manual provides detailed information about the SCSI interface and SCSI
commands that apply to Seagate DDS-4 and DAT 72 tape drives and autoloaders.
These drives offer electronically erasable, programmable, read-only memory (flash
EEPROM) for SCSI firmware, which enables qualified Seagate OEMs to download
revised firmware to the drive via two methods: using the SCSI bus or using a
specialized Seagate firmware tape cartridge.
About This Manual
The information in this manual applies to DDS-4 and DAT 72 drives and
autoloaders. For specific installation and operational information—including SCSI
connection information—refer to the Installation Guide or Product Description
Manual for the specific model of your drive or Autoloader. The following table
outlines the chapters in this manual.
Chapter Title Description
1 Introduction Introduces the SCSI interface and explains
2 SCSI Interface
3 Commands Lists and describes the SCSI commands.
Description
the structure of this manual.
Provides general information about the SCSI
interface for the DDS-4 and DAT 72 drives.
Page 2 DDS-4 SCSI Interface Manual, Rev. B
SCSI Interface Description
2
Overview
The Seagate DDS-4 and DAT 72 drives are designed to operate with the Small
Computer System Interface (SCSI) bus. This chapter discusses SCSI bus operation
as it pertains to drive functions.
SCSI is a standard interface established to support peripheral equipment such as
printers, tape drives, magnetic disks, optical disks for microcomputers and other
computer systems. The SCSI bus can support up to eight devices consisting of any
multiple of host adapters and peripheral devices.
The Seagate DDS-4 and DAT 72 drives comply with SCSI-2 and SCSI-3
specifications. In a few cases, vendor unique features are available. These features
are compatible with the SCSI standards.
The interface is a sixteen-port daisy-chained bus using twenty-seven signal lines:
eighteen data-bit signal lines and nine control lines. The eighteen data-bit lines are
made up of two pairs of eight data signal lines and one parity bit line. The remaining
nine lines provide control and status signals to coordinate data transfer operations
between the host controller and the selected drive.
The drives have an internal SCSI controller integrated into the drive electronics.
Each device ID on the SCSI bus may drive up to 8 logical units (LUN). These drives
support only LUN 0, except for the Autoloader, which also uses LUN 1.
ANSI SCSI Bus Standards
In addition to the information presented in this manual, we recommend that for
SCSI-2, read the ANSI Working Draft Revision 10 standard before writing host
software drivers. Also, see the conformance statements, which are given in the
Product Description Manual for the each model of drive or Autoloader.
Cabling and Connectors
The cabling requirements and pin outs for the SCSI connector for the internal drive
models are given in the respective installation guide and Product Description
Manual for each model of DAT drive or Autoloader.
SCSI Interface Description Page 3
Signal Descriptions
The drive SCSI interface consists of eighteen signals. Nine are control lines and
eighteen are data lines. Data lines include the parity signal option. These signals are
described in the following table.
Signal Name Description
-BSY
-SEL
-C/D
-I/O
-MSG
-REQ
-ACK
-ATN
-RST
DB(7-0)
DB(8-15)
DB(P0)
DB(P1)
NOTE: The BSY and RST signals are the only OR-tied signals. In ordinary bus operation, these
signals may be simultaneously driven by two or more drivers. There is no operational problem in mixing
OR-tied and three-state drivers on signals other than BSY and RST.
Busy OR-tied signal used to show that the data bus is in use
Select Signal used by an Initiator to select a Target or by a Target to
reselect an Initiator. SEL is driven by the Initiator during the
Selection Phase and driven by the Target during a Reselection
Phase.
Control/Data Target-driven signal used to indicate whether Control or Data
information is on the data bus. True (low) indicates Control, and
false (high) indicates Data.
Input/Output Target-driven signal used to control data movement direction on
the data bus with respect to an Initiator. This signal is also used to
distinguish between the Selection and Reselection Phases. True
(low) indicates input to the Initiator, and false (high) indicates
output from the Initiator.
Message Target-driven signal used to indicate the presence of a Message
Phase on the bus. True (low) indicates Message Phase, and false
(high) indicates Data, Command, or Status Phase.
Request Target-driven signal used to indicate a request for a REQ/ACK
data transfer handshake.
Acknowledge Initiator-driven signal used to indicate an acknowledgment for a
REQ/ACK data transfer handshake.
Attention Initiator-driven signal used to indicate the Initiator has a message
to communicate to the Target.
Reset OR-tied signal used to indicate a Reset condition.
Data Bus Eight data-bit signals plus a parity bit signal that form the odd
bytes of the data bus. DB (7) is the MSB and has the highest
priority (ID 7) during the Arbitration Phase.
Data Bus Eight data-bit signals that form the even byte of the data bus.
DB(15) is the MSB
Data Bus The data parity bit for the odd byte of the data bus. Parity is odd
and is a jumper-selectable option. Parity is not valid during the
Arbitration Phase. DB (P) is not to be driven False (high) during
the Arbitration Phase.
Data Bus Data parity bit for the even byte of the data bus.
Page 4 DDS-4 SCSI Interface Manual, Rev. B
Command Set Description
The following table shows the SCSI commands for sequential access devices
implemented by the drive and autoloader.
Code Type Command Group
00h M TEST UNIT READY 0
01h M REWIND 0
02h V REQUEST BLOCK ADDRESS 0
03h M REQUEST SENSE 0
05h M READ BLOCK LIMITS 0
07h A INITIALIZE ELEMENT STATUS 0
08h M READ 0
0Ah M WRITE 0
0Ch V SEEK BLOCK 0
10h M WRITE FILEMARKS 0
11h M SPACE 0
12h M INQUIRY 0
13h O VERIFY 0
15h M MODE SELECT 0
16h M RESERVE UNIT 0
17h M RELEASE UNIT 0
19h M ERASE 0
1Ah M MODE SENSE 0
1Bh O LOAD/UNLOAD 0
1CH O RECEIVE DIAGNOSTIC RESULTS 0
1Dh M SEND DIAGNOSTIC 0
1Eh O PREVENT/ALLOW MEDIUM REMOVAL 0
2Bh O LOCATE 1
34h O READ POSITION 1
3Bh O WRITE DATA BUFFER 1
3Ch O READ DATA BUFFER 1
44h M REPORT DENSITY SUPPORT (SCSI-3) 2
4Ch O LOG SELECT 2
4Dh O LOG SENSE 2
56H O RESERVE UNIT (SCSI-3) 2
57H O RELEASE UNIT (SCSI-3) 2
A5H A MOVE MEDIUM 5
A6H A EXCHANGE MEDIUM 5
B8H A READ ELEMENT STATUS 5
M = Mandatory Command V = Vendor Unique Command
O = Optional Command A = Autoloader Command Only
SCSI Interface Description Page 5
ANSI X3.131, 199x Conformance Statement (SCSI-2)
General features
• Disconnect/reconnect, arbitration (required in SCSI-2).
• Supports LVD and single-ended drivers.
• Fixed and variable block transfer lengths.
• Hard reset.
• Synchronous data transfers
• Parity implemented (switch option).
• Space blocks, filemarks, EOD, and setmarks.
• Supports third-party reservation
• Log Sense and Log Select for managing soft errors reporting.
• MODE SENSE/SELECT page to control and report operation of data
compression in sequential access devices.
• Complies with SCSI-2, Section 16, “Medium Changer Devices*.
Interface standards conformance
The Small Computer System Interface is described in standards including several
versions and a number of individual documents. The original Small Computer
System Interface Standard, X3.131-1986, is referred to herein as SCSI-1. SCSI-1
was revised resulting in the Small Computer System Interface – 2 (X3.131-1994),
referred to herein as SCSI-2. The set of SCSI-3 standards are collectively referred
to as SCSI-3. The applicable SCSI-3 standards are as follows:
SCSI-3 Architecture Model (SAM) X3.270:1996
SCSI Architecture Model - 2 (SAM-2) INCITS.366:2003
SCSI Parallel Interface - 2 (SPI-2) X3.302:1998
SCSI Parallel Interface - 3 (SPI-3) NCITS.336:2000
SCSI-3 Primary Commands (SPC) X3.301:1997
SCSI Primary Commands - 2 (SPC-2) NCITS.351:2001
SCSI-3 Medium Changer Commands (SMC) NCITS.314:1998
SCSI-3 Stream Commands (SSC) NCITS.335.2000
The term SCSI is used wherever it is not necessary to distinguish between the
versions of SCSI.
Page 6 DDS-4 SCSI Interface Manual, Rev. B
Commands
Erase Read Position
Exchange Medium* Release Unit
Initialize Element Status* Receive Diagnostic Results
Inquiry Report Density Support
Load/Unload Request Block Address
Locate Request Sense
Log Select Reserve Unit
Log Sense Rewind
Mode Select Seek Block
Mode Sense Send Diagnostic
Move Medium* Space
Prevent/Allow Media Removal Test Unit Ready
Read Verify
Read Block Limits Write
Read Data Buffer Write Data Buffer
Read Element Status* Write Filemarks
* Autoloader only commands
Messages
Abort Linked Command Complete with flag
Bus Device Reset Message Reject
Disconnect No Operation
Identify Parity Error Message
Ignore Wide Residue Save Data Pointer
Initiator Detected Error Synchronous Data Transfer Request
Linked Command Complete Wide Data Transfer Request
Vendor-unique commands
Seek Block Request Block Address
SCSI Bus Protocol
Communication on the SCSI bus occurs between a host computer's SCSI controller
and a peripheral controller. The host controller is the Initiator, and the peripheral
device is the Target.
Some SCSI bus functions are assigned to the Initiator and others to the Target. The
Initiator arbitrates (enters the Arbitration Phase of operation) for control of the SCSI
bus and enters the Selection Phase to select a specific Target such as a DAT drive.
The Target drive can request transfer of command, data, status, information, or
disconnect from the bus. While the tape drive is disconnected, the bus is free to
accomplish other tasks. While disconnected, the Target drive can process
information obtained from the bus. If the Target wants to reconnect, it arbitrates for
bus control. For example, a Target can reselect an Initiator or another Target to
continue an operation.
SCSI Interface Description Page 7
Data-transfer operations on the SCSI bus are either asynchronous or synchronous.
Asynchronous data transfer operations follow a defined request/acknowledge
(REQ/ACK) handshake protocol. Two eight-bit bytes of information can be
transferred with each REQ/ACK handshake. The default data transfer mode is
asynchronous.
Synchronous data transfer operations are initiated through the SYNCHRONOUS
DATA TRANSFER REQUEST message from the Initiator.
The SCSI bus protocol is divided into three modes or phases of operation: Waiting
Phases, Control Phases, and Information Transfer Phases. These phases are
further subdivided into the eight operational phases as listed in the following table.
Information on these operational phases is contained in the following paragraphs.
Waiting Phases Control Phases Information Phases
1. Bus Free 2. Arbitration 5. Command
3. Selection 6. Data (Data In/Data Out)
4. Reselection 7. Status
8. Message (Message In/
Message Out)
Waiting and Control Phases
The status of the SCSI bus is a function of the control signals. These signals define
the SCSI as in the Waiting Phase (Bus Free Phase), the Control Phases
(Arbitration, Selection, or Reselection), or the Information Transfer Phases
(Command, Data, Status, or Message). Seagate DDS-4 and DAT 72 drives support
both a SCSI system with Arbitration Phase and a SCSI system without Arbitration
Phase (non-arbitrating system).
Arbitrating Systems
In arbitration systems (required in SCSI-2), the sequence of SCSI bus phases
follows the sequence shown in Figure 2-1 on the following page. Operation begins
with the Bus Free Phase. Normal progression is from the Bus Free to the Arbitration
Phase. During Arbitration, Initiators and Targets assert for control of the SCSI bus.
The bus is awarded to the device with the highest priority SCSI bus address.
Page 8 DDS-4 SCSI Interface Manual, Rev. B
Figure 2-1
Phase Sequencing with Arbitration
RESET CONDITION
BUS FREE
PHASE
ARBITRATION
PHASE
SELECTION OR
RESELECTION
PHASE
COMMAND,
DATA, STATUS,
OR MESSAGE
PHASE
Arbitration is won by the highest priority SCSI device when both BSY and SEL are
asserted and a delay of at least 1200 nSec (1 bus clear delay + 1 bus settle delay)
occurs before the Arbitration Phase ends and the Selection Phase begins. Signal
timing is shown in Figure 2-3 and the complete Arbitration Phase protocol is
summarized in the following table.
Figure 2-2
Arbitration and Selection Phase Signal Timing
Step Procedure
1.
The SCSI device first waits for a Bus Free Phase to occur. The Bus
Free Phase is detected when both the BSY and SEL signals are
simultaneously and continuously false for a minimum of a bus settle
delay of 400 nSec.
SCSI Interface Description Page 9
2.
3.
4.
5.
NOTE: The single SCSI ID bit on the data bus corresponds to the unique ID code
of the SCSI device. All other SCSI data bus bits are released by the SCSI device.
Parity is not valid during the Arbitration Phase. During the Arbitration Phase, DB(P)
may be undriven or driven true, but not false.
The SCSI device waits a minimum of one bus free delay of 800 nSec
after detection of a Bus Free Phase before driving any signal. The Bus
Free Phase occurs after BSY and SEL are both false for a bus settle
delay of 400 nSec.
Following the 800 nSec Bus Free Delay in Step 2, the SCSI device
Arbitrates for the SCSI bus by asserting both BSY and its own SCSI ID;
however, the SCSI device does not assert a BSY and its SCSI ID if
more than a bus settle delay (1.8 Sec) has passed since the Bus Free
Phase was last observed.
After waiting at least an Arbitration delay (2.2 Sec) measured after
asserting a BSY signal, the SCSI device examines the data bus. If a
higher priority SCSI ID bit is true, then the SCSI device loses the
Arbitration. The SCSI device releases its signals and returns to Step 1. If
no higher priority SCSI ID bit is true on the bus, then the SCSI drive
wins the Arbitration and asserts the SEL signal. Any other device that
participated in the Arbitration Phase and lost Arbitration releases BSY
and its SCSI ID bit within a bus clear delay after SEL becomes true. A
SCSI device that loses Arbitration returns to Step 1.
The SCSI device that wins Arbitration waits at least one bus clear delay
plus a bus settle delay of 1,200 nSec after asserting the SEL signal and
changing the condition of other signals.
Selection and Reselection Phases
The Selection and Reselection Phases provide a method for establishing a link
between the Initiator and Target. When selected by an Initiator that supports
disconnects, the Target has the option of disconnecting from the SCSI bus. When
the Target needs to again establish the link to its original Initiator, the Target
reselects that Initiator.
When selection is made, no restrictions on the sequences between Information
Transfer Phases exist. A phase type may be followed by the same phase type. For
example, a data phase may be followed by another data phase.
A device that wins Arbitration assumes the roll of Initiator by releasing the I/O signal.
The Initiator sets the data bus to a value that is the OR of its SCSI ID bit and the
Targets ID bit. The Initiator waits at least two deskew delays (90 nSec) before
releasing the BSY signal and an additional bus settle delay (400 nSec) before
looking for a response from the Target.
A device that loses Arbitration must release the Select ID and BSY.
Operation enters the Selection or Reselection Phases when a particular device wins
a request in Arbitration and gains control of the SCSI bus. These phases allow the
device in control of the bus to select another specific device connected to the SCSI
bus for communication.
Page 10 DDS-4 SCSI Interface Manual, Rev. B
For example, the Initiator can select a tape drive to begin an operation, or the tape
drive can reselect an Initiator to continue an operation previously disconnected. The
tape drive does not disconnect from the bus unless the host asserted the host ID bit
during selection and the host sent an Identify message of C0h.
The Selection and Reselection Phases can be terminated for either of the following
reasons:
• A Selection/Reselection time-out occurs. A Target or Initiator did not respond to
a Selection or Reselection Phase within a maximum abort time of 200 Sec.
• A reset signal occurs on the SCSI bus. All sequences are terminated, and
signals are released by all Targets and Initiators.
The Initiator can use the ATN signal to notify the DAT drive that an IDENTIFY
message from the Initiator is ready. To ensure that the Target recognizes the
Attention condition before the Command Phase is entered, the ATN signal must be
low before SEL is asserted and BSY de-asserted.
Select With Attention
The host system can select the drive only using Select With Attention. The Select
With Attention allows the host to send the Identify message to specify that the host
supports disconnect.
The host can also use the Select With Attention to send messages other than the
Identify message. For example, a Bus Device Reset or Abort message can be sent
to cause the drive to reset itself without affecting any other device on the SCSI bus.
The DAT drive responds appropriately to the host messages.
If the drive receives an illegal message, it enters the Message Out Phase and sends
the Reject message to the host. If any reserved bit (bits 5, 4, or 3) is set, an Identify
message is rejected.
Responses to Identify messages with a non-zero LUN are described in the following
subsection.
Identify Message
Because the drive only supports Logical Unit 0, the Identify message is used solely
to specify the Disconnect option. The bit map for the Identify message is as follows:
Bits 7 6 5 4 3 2 1 0
| DIS | Reserved | LUN
If bit 7 is set, the Identify message is indicated. Bit 6 (shown as DIS) is set as
follows:
0 The host does not support disconnects. The drive does not disconnect from the
SCSI bus during the current command.
SCSI Interface Description Page 11
1 The host supports disconnects. The drive disconnects from the SCSI bus
appropriately for the command in progress to relinquish the bus for other units.
Note: LUN = 1 is legal for Autoloader drives only.
Information Transfer Phases
The Command, Data, Status, and Message Phases are grouped together as the
Information Transfer Phases because they are all used to transfer data or control
information on the SCSI bus.
The following table shows the Control Data (C/D), Input/Output (I/O), and Message
(MSG) signals used to distinguish between the various Information Transfer Phases.
The Target drives these three signals and thereby controls all changes from one
phase to another.
Signals -MSG -C/D -I/O Phases Direction of Transfer
-I/O
1 1 0 Data Target to Initiator
-C/D
1 0 0 Status Target to Initiator
-MSG
0 0 0 Message Target to Initiator
Key: 1 = False, 0 = True
1 1 1 Data Initiator to Target
1 0 1 Command Initiator to Target
0 0 1 Message Initiator to Target
Information Transfer Phases use one or more REQ/ACK handshakes to control the
information transfer. Each REQ/ACK handshake allows the transfer of one byte of
information. During the information transfer phases, BSY remains true and SEL
remains false. C/D, I/O, and MSG control signals are valid for a bus settle delay of
400 nSec before assertion of REQ signal at the first handshake and remain valid
until negation of ACK at the end of the last handshake.
Asynchronous Data Transfer
The Target controls the direction of information transfer with the I/O signal. When
I/O is asserted (low), information is transferred from the Target to the Initiator. When
I/O is de-asserted (high), information is transferred from the Initiator to the Target.
Figure -4 shows the data transfer signals for information transfer from Target to
Initiator, and Figure 2-5 shows the data transfer signals for information transfer from
Initiator to Target. Each direction of information transfer is discussed in detail in the
following paragraphs.
Transfer from Target to Initiator
The transfer from Target to Initiator is described in the following table and illustrated
in Figure 2-4.
Timing Point Action
t1
t2
The I/O signal is asserted; the Target drives the data (DB7-0)
and parity signals to their desired values.
The Target then asserts the REQ signal.
Page 12 DDS-4 SCSI Interface Manual, Rev. B
t3
The Initiator reads the data and parity signals after REQ is
asserted and then signals its acceptance of the data by asserting
the ACK.
t4
t5
ACK goes low at the Target, and the Target de-asserts REQ.
The REQ signal is false. The Initiator de-asserts ACK. After the
ACK signal is high, the Target can continue the transfer by
repeating the steps from t1.
Figure 2-4
Signals Used in Transfer from Target to Initiator
Transfer from Initiator to Target
Transfer from Initiator to Target is described in the following table and illustrated in
Figure 2-5.
Timing Point Action
t1
The I/O signal is de-asserted, and the Target asserts REQ to
request information.
t2
The Initiator drives the data and parity signals to their desired
values.
t3
t4
The Initiator asserts the ACK.
The Target de-asserts REQ, signaling its acceptance of data.
The Initiator then releases the data and parity signals.
t5
The Initiator de-asserts ACK. The Target can then continue to
transfer by asserting the REQ signal.
SCSI Interface Description Page 13
Figure 2-5
Signals Used in Transfer from Initiator to Target
Synchronous Data Transfer
Both the Initiator and Target must send a SYNCHRONOUS DATA TRANSFER
REQUEST (SDTR) message in order to set up synchronous data transfer
parameters. The drives supports both SDTR WDTR extended (multibyte) messages.
The host may initiate an SDTR to establish a new synchronous data transfer
agreement or to end a previously arranged synchronous data transfer agreement
and return to asynchronous data transfer mode.
The following table shows the format for the SDTR message.
Byte Value Description
0
1
2
3
4
* Transfer Period can be any value between 0Ah and 64h. Exceptions to m x 4 nsec are
made in the following cases: 1) If the value is 0Ch, which is defined in SCSI-3 as a period
of 50 nsec, 2) If the value is 0Bh, which sets the period to 37.5 nsec, and 3) If the value is
0Ah, which sets the period to 25 nsec
** REQ/ACK Offset can be any value between 4 and 32.
01h Extended message
03h Extended message length
01h Synchronous Data Transfer Request Code
m* Transfer Period (m x 4 nsec)
** REQ/ACK Offset
.
The Transfer Period is the minimum time allowed between leading edges of
successive REQ pulses and of successive ACK pulses to meet the requirements of
the drive for successful reception of data. The host and DAT drive can transfer data
with larger, but never smaller, Transfer Period than specified in the SDTR message.
Page 14 DDS-4 SCSI Interface Manual, Rev. B
The minimum value fo the Transfer Period (25 nsec) is determined by the maximum
burst transfer rate of the SCSI interface hardware of the drive and is 80 Mbytes per
second (06h). The host must specify a Transfer Period that allows it to successfully
receive data from the DAT drive during the Data In Phase. Transfer Period
represents the actual transfer period, in nanoseconds, divided by 4.
The REQ/ACK Offset is the maximum number of pulses that can be sent by the DAT
drive in advance of the number of ACK pulses received from the host, establishing a
pacing mechanism. If the number of REQ pulses is greater than the number of ACK
pulses by the REQ/ACK Offset, the DAT drive stops sending data until after the
leading edge of the next ACK is received.
The ACK/REQ Offset is used to prevent an overflow condition in the host's reception
buffer during the Data In Phase. The REQ/ACK Offset should be set to the size of
the host's reception buffer minus one.
To set up a new synchronous data transfer agreement, the host asserts the ATN
signal and sends an SDTR message. The Transfer Period must be set to one of a
set of specific values equal to or greater than 0Ah and less than the maximum rate
of the host’s reception buffer. The ACK/REQ Offset will be set to a nonzero value
between 4 and the size of the host’s reception buffer minus 1, but it must not exceed
32.
If the Transfer Period and the ACK/REQ Offset are within the ranges described
above, the DAT drive goes to the Message In Phase and returns an SDTR message
with the same Transfer Period and ACK/REQ Offset. This return indicates a
successful completion of the SDTR message exchange. The implied synchronous
data transfer agreement remains in effect until:
• A Bus Device Reset message is received.
• A hard reset condition occurs.
• The successful completion of the next SDTR message exchange.
If the Transfer Period is less than 0Ah or the REQ/ACK Offset less than 4 the drive
returns either a Transfer Period of zero or a REQ/ACK Offset of zero to indicate the
request cannot be supported in a synchronous manner and use of asynchronous
transfer is requested.
If the host specifies a REQ/ACK offset of zero, the DAT drive operates in the
asynchronous data transfer mode.
Command Phase
During the Command Phase, the Target requests command information from the
Initiator. The Target asserts the C/D signal and de-asserts the I/O and MSG signals
thus denoting the Command Phase. The REQ/ACK then handshakes the command
bytes across the SCSI bus (Figure 2-5). The command bytes are also called the
Command Descriptor Block (CDB).
SCSI Interface Description Page 15
Data Phase
The Data Phase is subdivided into the Data-In and Data-Out Phases.
Data-In Phase
During the Data-In phase, the Target requests that data be sent to the Initiator from
the Target. The Target asserts the I/O signal and de-asserts the C/D and MSG
signals thus denoting the Data-In Phase. The REQ/ACK handshakes (Figure 2-4)
then transfer the requested byte count.
Data-Out Phase
During a Data-Out phase, the Target requests that data be sent from the Initiator to
the Target. The Target de-asserts the C/D, I/O, and MSG signals thus denoting the
Data-Out Phase. The REQ/ACK handshakes (Figure 2-5) then transfer the
requested byte count across the SCSI bus.
Status Phase
Message Phase
Message-In Phase
Message-Out Phase
During a Status Phase, the Target requests that status information be sent to the
Initiator from the Target. The Target asserts the C/D and I/O signals and de-asserts
the MSG signal thus denoting the Status Phase. The REQ/ACK handshakes the one
byte status code across the SCSI bus (refer to Figure 2-4).
The Message Phase consists of either the Message-In or Message-Out Phases.
The Seagate DDS-4 and DAT 72 drive supports one-byte messages.
During the Message-In Phase, the Target requests that messages be sent to the
Initiator from the Target. The Target asserts the C/D, I/O, MSG signals thus
denoting the Message-In Phase. The REQ/ACK handshakes the one-byte message
across the SCSI bus.
During the Message-Out Phase, the Target requests that messages be sent from
the Initiator to the Target. The Target invokes this phase in response to the Attention
(ATTN) signal asserted by the Initiator. The drive responds to the ATTN signal at
every phase change. The Target asserts the C/D and MSG signals and de-asserts
the I/O signal, denoting the Message-Out Phase. The REQ/ACK handshakes the
one byte message across the SCSI bus. The Target uses REQ/ACK handshakes
(Figure 2-5) until the ATN signal becomes false, unless an error occurs and the
message is rejected.
Page 16 DDS-4 SCSI Interface Manual, Rev. B
Command Descriptor Block
A request to a peripheral device is performed by sending a Command Descriptor
Block (CDB) to the Target. For several commands, the request is accompanied by a
list of parameters sent during a Data Out Phase. If an invalid parameter is contained
in the CDB, the drive terminates the command without altering the medium.
The Seagate DDS-4 and DAT 72 drives implementation supports Group 0 and
selected Group 1 and Group 2 commands. Group 0 CDBs are six-bytes. Group 1
and 2 CDBs are ten-bytes.
The CDB contains both reserved bit fields and defined bit fields. Defined bit fields
are: Group Code, Command Code, Logical Unit Number (LUN), Vendor Unique
(VU), Flag, and Link, whereas reserved bit fields are defined by zeros such as those
appearing on the last line of the following table. This table shows a typical Group 0,
six-byte, Command Descriptor Block.
Note: The LUN field must be 0 in the CDB. Target LUN numbers are sent in the
Identify Message.
Byte
0 Group Code Command Code
1 LUN Command Dependent
2 Command Dependent
3 Command Dependent
4 Command Dependent
5 VU VU 0 0 0 0 Flag Link
7 6 5 4 3 2 1 0
Bits
The following table shows a typical Command Descriptor Block for Group 1 and 2
commands.
Byte
0 Group Code Command Code
1 LUN Command Dependent
2 Command Dependent
3 Command Dependent
4 Command Dependent
5 Command Dependent
6 Command Dependent
7 Command Dependent
8 Command Dependent
9 VU VU 0 0 0 0 Flag Link
7 6 5 4 3 2 1 0
Bits
The following table describes the CDB fields common to all Group 0, 1, and 2
commands.
CDB Field Description
SCSI Interface Description Page 17
Group Code* This field indicates which of eight possible SCSI command groups is specified.
Seagate drives support Group 0.
Command
Code*
Logical Unit The LUN must be set to zero.
Vendor Unique When set, these bits select vendor unique functions in specified commands.
Flag bit The Flag bit is used only in conjunction with the Link bit and must be set to zero if
Link bit** The Link bit is used to indicate that the Initiator desires automatic linking to the next
* Together, group code and command code make up the op code.
** If the Link bit is used, all applicable commands must have the Immediate bit set to zero or a Check
Condition status is returned and Extended Sense Key is set to Illegal Request.
This field indicates which of 32 possible command codes for a particular group
code is specified.
the Link bit is zero. When the Link bit is set, the value of the Flag bit determines the
appropriate message to send to the Initiator when a linked command completes
successfully. A 0 value indicates that the Linked Command Complete message is
required. A 1 value indicates that the Linked Command Complete with Flag
message is required. Typically, the Flag bit is used to cause an interrupt in the
Initiator at the end of, or at logical intervals in, linked command processing.
command on successful completion of the current command. When the Link bit is
one, on successful termination of the command, the drive returns an Intermediate
Status followed by one of the two Command Complete messages as determined by
the Flag bit. (Refer to description of Flag bit above.)
Logical Unit Support
The Seagate DDS-4 and DAT 72 drive only supports Logical Unit (LUN) 0, except
for the Autoloader, which supports both LUN 0 and LUN 1. However, it responds to
a host command that tries to select or identify any other LUN. The response of the
drive to illegal LUNs varies depending on the command and the manner in which the
host specifies the LUN.
The host can specify an LUN I only by sending an Identify message after the
Selection Phase
Because of the redundancy of specifying the LUN, the Seagate DDS-4 and DAT 72
drive responds appropriately if the LUN is specified in both the Identify message and
in the CDB. If the drive is selected and a valid Identify message is received with
LUN = 0 (or LUN = 1 if the drive is an Autoloader), the LUN field of the CDB is
ignored. Thus, the Identify message overrides the CDB LUN specification.
Because the SCSI INQUIRY command determines what LUNs a particular SCSI
device supports, the response from the drive to this command is unique. With the
INQUIRY command when the drive receives an unsupported LUN, the command
completes normally. The drive indicates that it does not support the specified LUN
by returning a 7F hexadecimal value in byte 0 of the INQUIRY data. Regardless of
what method is used to specify the LUN, the 7F hex value is returned.
If an unsupported LUN is specified for a REQUEST SENSE command, the
command completes normally with Good Status, and the sense data is set to Illegal
Request.
For all other commands, the illegal LUN is detected in the Identify message. If an
illegal LUN is specified in the Identify message, the drive enters the Command
Phase and accepts the CDB. It immediately skips to the Status Phase and posts a
Check Condition. The Sense data is set to Illegal Request. If the Identify message is
correct, the CDB LUN is ignored.
Page 18 DDS-4 SCSI Interface Manual, Rev. B
SCSI Message Descriptions and Definitions
The SCSI message codes, descriptions, and directions are given in the following
table. Each of these SCSI messages is supported by the Seagate DDS-4 drive.
Code Description Direction*
00h
02h
03h
04h
05h
06h
07h
08h
0Ah
0Bh
0Ch
80h
C0h
01h**
* Direction: In = Drive to host; Out = Host to drive.
** Supports only two extended messages: Synchronous Data Transfer Request
and Wide Data Transfer Request.
Command Complete In
Save Data Pointer In
Restore data pointers In
Disconnect In
Initiator Detected Error Out
Abort Out
Message Reject In/Out
No Operation Out
Linked Command Complete In
Linked Command Complete with Flag In
Bus Device Reset Out
Identify (when sent by host, disables
Disconnect/Reconnect)
Identify (enable Disconnect/Reconnect) Out
Extended Message In/Out
In/Out
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