
S T 3 2 5 5 0 N   B A R R A C U D A 2 L    SEAGATE
                                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 3.5"/SLIMLINE         Cylinders    3711|     |     |
Capacity form/unform  2147/ 2541 MB        Heads          11|     |     |
Seek time   / track   8.5/ 0.8 ms          Sector/track     |     |     |
Controller           SCSI2 SI/FAST         Precompensation
Cache/Buffer           512 KB SEGMENTED    Landing Zone
Data transfer rate    5.500 MB/S int       Bytes/Sector      512
                     10.000 MB/S ext SYNC
Recording method     RLL 1/7                        operating  | non-operating
                                                  -------------+--------------
Supply voltage     5/12 V       Temperature *C         5 50    |    -40 70
Power: sleep              W     Humidity     %                 |
       standby            W     Altitude    km                 |
       idle           8.8 W     Shock        g                 |
       seek               W     Rotation   RPM      7200
       read/write         W     Acoustic   dBA
       spin-up            W     ECC        Bit
                                MTBF         h     800000
                                Warranty Month        60
Lift/Lock/Park     YES          Certificates


**********************************************************************
                        L   A   Y   O   U   T
**********************************************************************
SEAGATE  ST31250/32550N/ND/W/WC/DC/WD  INSTALL. GUIDE 83328920 REV E


  +---------------------------------------------------------+
  |1-+                                                      |XX
  || |J4                                                    |XXI
  || |                                                      |XXN
  |+-+                                                      |XXT
  |                                                         |XXE
  |        N/ND Models                                      |XXR
  |                                                         |XXF
  |                                                         |XXA
  |                                                         |XXC
  |                                                         |XXE
  |                                                         |XX
  |                                           4 Pins on ND  |XX
  |                                           Models        |XX
  |                                              +--6J1     |
  |                             J2               1--+       |XXPOWER
  |                              +-------1                  |XX
  +------------------------------+-------+------------------+







  +---------------------------------------------------------+
  |1-+                                                      |+--+I
  || |J4                                                    ||XX|N
  || |                                                      ||XX|T
  |+-+                                                      ||XX|E
  |                                                         ||XX|R
  |        W/WD Models                                      ||XX|F
  |                                                         ||XX|A
  |                                                         ||XX|C
  |                                                         ||XX|E
  |                                                         |+--+1
  |                                                         |+-+J5
  |                                            4 Pins on    || |
  |                                            WD Models    || |
  |                                              +--+J1     |+-1
  |                             J2               1--+       |XXPOWER
  |                              +-------1                  |XX
  +------------------------------+-------+------------------+  1



**********************************************************************
                      J   U   M   P   E   R   S
**********************************************************************
SEAGATE  ST31250/32550N/ND/W/WD/WC/DC  INSTALL.GUIDE 83328920 REV.E 95

 Jumper Setting
 ==============

 J4 Setting the SCSI ID jumpers N/ND Models
 ------------------------------------------
 Use the J4 connector to set the SCSI ID. To change the SCSI ID,
 install jumpers on the appropriate pins as shown.

 ---+---------------------+-
    | 2 o o * * * o o o o |    (Front View)
    | 1 o o * * * o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o * * * o o o o |    SCSI ID 0 (DEFAULT)
    | 1 o o * * * o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o X * * o o o o |    SCSI ID 1
    | 1 o o X * * o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o * X * o o o o |    SCSI ID 2
    | 1 o o * X * o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o X X * o o o o |    SCSI ID 3
    | 1 o o X X * o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o * * X o o o o |    SCSI ID 4
    | 1 o o * * X o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o X * X o o o o |    SCSI ID 5
    | 1 o o X * X o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o * X X o o o o |    SCSI ID 6
    | 1 o o * X X o o o o |J4
    +---------------------+

 ---+---------------------+-
    | 2 o o X X X o o o o |    SCSI ID 7
    | 1 o o X X X o o o o |J4
    +---------------------+


 SCSI ID jumpers
 ---------------
 Each device on the SCSI chain must have a unique SCSI ID. The
 host system's SCSI controller usually uses the highest-numbered
 ID available; therefore the lower-numbered SCSI IDs are normally
 used for the other SCSI devices such as this Barracuda disc drive.

 NOTE
 Most SCSI controllers (host adapters) allow you to skip a SCSI ID.
 For example, you can have ID0, ID1, and ID3 (skipping ID2). Other
 controllers do not allow this so be sure to refer to your system or
 controller user's manual for details about its requirements for
 proper SCSI device installation.

 Most Barracuda disc drives are factory set with the SCSI ID set
 at 0. If, after completing the installation process, the drive's
 LED does not show on/off activity when the host is trying to
 communicate with the drive, a duplicate SCSI ID may be the
 problem. If this is the case, change the ID so that each device
 on the SCSI chain has its own unique ID.

 Also check your system or controller user's manual to ensure that
 you have not violated its SCSI ID numbering recommendations.


 WC/DC drives
 ------------
 Setting the SCSI ID jumpers
 The SCSI ID for WC drives is normally set over the SCSI bus by the
 host system using connector contacts 39 (ID0), 40 (ID2), 79 (ID1),
 and 80 (ID3). Systems designers may, optionally, install a remote
 operator panel connection to set the SCSI ID.


 J1 Terminating the drive N/ND
 -----------------------------
 +-------+
 | X * 1 | J1  Enable SCSI terminator (DEFAULT)
 | X * * |
 +-------+
 +-------+
 | * * 1 | J1  Disable SCSI terminator
 | 6 * * |
 +-------+

 If you are installing a Barracuda 2LP drive in a system that has
 other SCSI devices installed, terminate only the end devices on
 the SCSI chain. A SCSI "device" is any disc drive, scanner, tape-
 backup unit, or other piece of hardware connected to your system
 using the SCSI bus.

 N/ND drives
 -----------
 ST31250N and ST32550N drives are terminated with permanently mounted
 IC active terminators. If you install one of these drives and it is
 not on the end of the SCSI bus, disable the terminators by removing
 the jumper from pins 5 and 6 of connector J1. If you install the
 drive on the end of the SCSI bus, enable termination by installing
 a jumper on pins 5 and 6 of connector J1.

 NOTE
 Use active terminators when terminating the bus.

 ST31250ND and ST32550ND drives do not have internal terminators or
 any other way of adding internal termination to the drive. You
 must provide external active termination (ANSI SCSI-2 Alternative
 2) to these drives when termination is required.


 Terminating the drive (W Models)
 --------------------------------
 ST31250W and ST32550W drives are terminated with permanently mounted
 IC active terminators. If you install one of these drives and it is
 not on the end of the SCSI bus, disable the terminators by removing
 the jumper from pins 5 and 6 of connector J1. If you install the
 drive on the end of the SCSI bus, enable termination by installing a
 jumper on pins 5 and 6 of connector J1.

 NOTE
 Use active terminators when terminating the bus.

 ST31250WD and ST32550WD drives do not have internal terminators or
 any other way of adding internal termination to the drive. You must
 provide external active termination (ANSI SCSI-2 Alternative 2) to
 these drives when termination is required.


 Terminating the drive WC Models
 -------------------------------
 ST31250WC and ST32550WC drives do not have internal terminators or
 any other way of adding internal termination to the drive. You must
 provide single-ended external active termination (ANSI SCSI-2
 Alternative 2) to these drives when termination is required.


 Terminator power
 ----------------
 You usually will not need to change this option and can normally
 leave the drive configured as it was shipped from the factory.
 For information about how to change the terminator power option on
 your drive.


 Terminator power W Models
 -------------------------
 There are four possible terminator power configurations for ST31250W
 and ST32550W drives. You will not normally need to change this option
 and can leave the drive configured as it was shipped from the
 factory.

 ST31250WD and ST32550WD drives should be configured with a jumper
 connecting J1 pins 1 and 3 (and no jumper on J1 pins 2 and 4).


 J1 Teminator Power N MODELS
 ---------------------------
 +-------+
 | * * X | J1  Terminator power from drive (DEFAULT)
 | 6 * X |
 +-------+
 +-------+
 | * xxx | J1  Terminator power to SCSI bus
 | 6 * * |
 +-------+
 +-------+
 | * * 1 | J1  Terminator power from SCSI bus
 | 6 xxx |
 +-------+
 +-------+
 | * xxx | J1  Terminator power to SCSI bus and drive
 | 6 xxx |
 +-------+


 J1 Terminator Power ND MODELS
 -----------------------------
 +-----+
 | xxx | J1  Terminator power to SCSI bus
 | * *2|
 +-----+

 There are four possible terminator power configurations for ST31250N
 and ST32550N drives. You will not normally need to change this option
 and can leave the drive configured as it was shipped from the
 factory.

 ST31250ND and ST32550ND drives should be configured with a jumper
 connecting J1 pins 1 and 3 (and no jumper on J1 pins 2 and 4).


 J4 Synchronizing spindles N/ND Models
 -------------------------------------

          + Spindle Sync Reference
 ---+-----+---------------+-
    | 2 o * o o o o o o o |    (Front View)
    | 1 o * o o o o o o o |J4
    +-----+---------------+
          + Spindle Sync Ground

 If you are installing two or more Barracuda drives, you may
 (optionally) synchronize their spindles to reduce the latency
 associated with switching from one drive to another. Spindle sync
 cables are used to connect the drives.

 After connecting each drive with spindle sync cables, designate a
 master spindle sync reference source. This master source is normally
 a disc drive located on the same SCSI bus as the other drives you
 want to synchronize with. To designate a drive as the master, use
 SCSI interface commands.


 Synchronizing spindles WC Models
 --------------------------------
 Spindle synchronization for WC drives is normally handled on the
 SSCI bus by the host system using connector contact 37 for the
 spindle sync reference signal. System designers may, optionally,
 install a spindle sync cable using pin 6 on the J4 connector to
 provide +SSREF.

    +-- Spindle Sync Reference
   ++--J5------1 Power
   |o o o o o o| XXXXXXXX
   |o o o o o o| XXXXXXXX
   ++----------+
    +-- Spindle Sync Ground


 J4 RESERVED
 -----------
 ---+---------------------+-
    | x o o o o o x x x x |    (Front View)
    | x o o o o o x x x x |J4  x = RESERVED
    +---------------------+


 J4 Remote LED
 -------------
        +- GND (Cathode)
 ---+---+-----------------+-
    | 2 o o o o o o o o o |    (Front View)
    | 1 o o o o o o o o o |J4
    +---+-----------------+
        +- POS (Anode)

 NOTE
 Note to subsystem designers: In Europe, a red LED indicates an error
 or warning condition. For this reason, you may want to use a color
 other than red with this connection.


 J2 Other applicable jumper options N/ND Models
 ====================================================================
 ---+-------------------+-
    | x x o o o o x x x |    (Front View)
    | x x o o o o x x x |J2  x = RESERVED
    +-------------------+


 Parity Check Option
 -------------------
 ---+-------------------+-
    | 2 o * o o o o o o |    Enables parity check of SCSI bus
    | 1 o * o o o o o o |J2  (DEFAULT)
    +-------------------+
 ---+-------------------+-
    | 2 o X o o o o o o |    Diables parity check
    | 1 o X o o o o o o |J2
    +-------------------+


 Write Protect Option
 --------------------
 ---+-------------------+-
    | 2 o o * o o o o o |    Write Protect Disabled (Default)
    | 1 o o * o o o o o |J2  Enable writing
    +-------------------+

 ---+-------------------+-
    | 2 o o X o o o o o |    Write Protect Enabled
    | 1 o o X o o o o o |J2  Drive is write protected!
    +-------------------+


 Motor Start Option
 ------------------
 ---+-------------------+-
    | 2 o o o X o o o o |    Enable motor start. The drive waits for
    | 1 o o o X o o o o |J2  the Start Unit command from host before
    +-------------------+    starting the spindle motor.

 ---+-------------------+-
    | 2 o o o * o o o o |    Disable motor start (default). The
    | 1 o o o * o o o o |J2  drive starts according to the Delay
    +-------------------+    Motor Start option.


 Delay Motor Start Option
 ------------------------

 Delay Motor Start option (valid only if the Motor Start jumper is
 not connected)
 ---+-------------------+-
    | 2 o o o o * o o o |   Disable the Delay Motor Start option.
    | 1 o o o o * o o o |J2 DEFAULT
    +-------------------+

 ---+-------------------+-
    | 2 o o o o X o o o |    Motor start delay equal to the SCSI ID
    | 1 o o o o X o o o |J2  multipled by 10 seconds. For example, if
    +-------------------+    the SCSI ID = 2, the drive starts in 20
                             seconds.


  REAR VIEW

         50 pin I/O Cable Connection
         |                         POWER
      +------------------------1+ /---------\    TOP (HDA)
     -+:::::::::::::::::::::::::+-+ O O O O +---------
      +-------------------------+ +-5-G-G-12+    BOTTOM

  These pins not on differential --> (o o)  back
  model ND                  +------   o o
                            |         o o   front
                            |        2   1
                            |
  +- J1 Terminator options -+- (single-ended) -----------+
  |      o o       o o       o o       o o       xxx     |
  |      o o       o x       x o       x x       o o     |
  |      xxx       o X       X o       X X       o o     |
  |     2   1     2   1     2   1     2   1     2   1    |
  |      A         B         C         D         E       |
  +------------------------------------------------------+
  A - Term. power from drive (default)
  B - Term. power to SCSI bus (only option available for differential
      ND)
  C - Term. power from SCSI bus
  D - Term. power to SCSI bus and drive
  E - Enable SCSI terminator (jumper on pins 5-6)


  RIGHT SIDE VIEW  (ST-31250N)


 BACK   +-+      J2  123456789                   TOP (HDA)  FRONT
 OF    I/O+---------------------P-W-A----------------------- OF
 DRIVE  +-+          :::::::::                   BOTTOM     DRIVE
                     |||||||||
      1-2 RESERVED --++||||+++-- RESERVED 7-9
  3 Parity Disable ----+||+----- Delay Motor Start 6
   4 Write Protect -----++------ Motor Start Enable 5


   FRONT VIEW  (ST-31250N)

                                     J4
                      TOP (HDA)  +----------1
    ---P-W-A---------------------+::::::::::+-------
                                 ++++++++++++
                      BOTTOM      ||||||||||
                                  ||||||||||
                        RESERVED -++++|||||+- RESERVED
                            ID 4 -----+|||+-- Remote LED (pin-3 +5V)
                            ID 2 ------+|+--- Spindle Synchronization
                            ID 1 -------+      (pin-6 REF SIG+)


 Enabling write cache
 --------------------
 Write caching is a feature that allows the drive to transfer write
 data to its own cache, tell the controller that the task is complete,
 and then actually complete the write at a later time. This improves
 write performance by freeing the CPU to go on to its next command.

 WARNING
 Information can be lost is you enable write cache and there is a
 system failure (for example, power failure) before the data has
 actually been physically written to the disc.

 OEM drives are shipped with write cache disabled by default. If
 you want to enable the write cache, refer to your system's drive
 controller and software utility documentation. Seagate provides an
 ASPI utility that you can use in a PC compatible system to enable
 the write cache.



**********************************************************************
                      I   N   S   T   A   L   L
**********************************************************************
SEAGATE  ST31250/32550N/ND/W/WD/WC/DC INSTALL. GUIDE 83328920, REV. E

 Notes on installation
 =====================

 Installation direction
 ----------------------

     horizontally                           vertically
   +-----------------+             +--+                       +--+
   |                 |             |  +-----+           +-----+  |
   |                 |             |  |     |           |     |  |
 +-+-----------------+-+           |  |     |           |     |  |
 +---------------------+           |  |     |           |     |  |
                                   |  |     |           |     |  |
                                   |  |     |           |     |  |
 +---------------------+           |  +-----+           +-----+  |
 +-+-----------------+-+           +--+                       +--+
   |                 |
   |                 |
   +-----------------+

 The drive will operate in all axis (6 directions).


 Mounting the drive and connecting cables
 ----------------------------------------
 Do not touch the connector pins or any components on the control
 board without observing static-discharge precautions. Always handle
 the drive by the frame only.

 The drive may be mounted in any orientation (horizontally,
 vertically, and any combination thereof); however, you must ensure
 that the drive receives adequate air flow for cooling.

 1. Mount the drive to the host system's chassis using four 6-32
    UNC screws. Two mounting holes are in each side of the drive
    and there are four mounting holes in the bottom of the drive.

    The maximum length that the screws should extend into the chassis
    mounting holes is 0.15 inch (3.81 mm), measured from the outer
    surface of the chassis. Tighten the screws down evenly. Do not
    overtighten or force the screw if it does not seem to screw in
    easily, because this means the threads are not properly aligned.
    In this case, back the screw out and try again.

 2. Verify that all connections between the drive and the host system
    are correctly installed.

 3. Verify that you have correctly installed jumpers.

 4. Connect the 50-pin SCSI cable into the drive's SCSI connector.
    Take care not to stretch or crimp this cable, and do not block
    the system's cooling air flow with the cable.

   The drive receives DC power through a 4-pin connector mounted next
   to the SCSI connector. The output of a power supply must meet SELV
   (safety extra low voltage) as defined in IEC 950. To connect the
   DC power cable to the drive, insert the cable end into the drive's
   DC power connector.

 NOTE
 Signal ground on the power control board (PCB) and the head and
 disc assembly (HDA) are connected together in this drive and you
 cannot separate them. The equipment in which you have mounted the
 drive is connected directly to the HDA and PCB without electrically
 isolating shock mounts. Maximizing the conductive contact area
 between HDA ground and system ground may reduce radiated emissions.
 If you do not want the system chassis to be connected to the HDA/PCB
 ground, you must provide a nonconductive (electrically isolating)
 method of mounting the drive in the host system. This may increase
 radiated emissions and is the system designer's responsibility.

 5. Replace the host system's cover.

 This mounting procedure does not apply to WC or DC model drives!
 To mount a WC or DC drive, plug the drive into the system's single
 connector attachment (SCA) position on the system's back panel.


 Providing adequate cooling
 --------------------------
 The enclosure design must ensure adequate cooling for the drive.
 The maximum ambient temperature is 50*C.

 We recommend orienting the drive or directing the air flow in a
 way that creates the least amount of air-flow resistance while
 providing air flow above the circuit boards and around the head and
 disc assembly (HDA). Also, choose the shortest possible path between
 the air inlet and exit. This minimizes the distance traveled by air
 that is heated by the drive and by other nearby heat sources.


 DC Power
 --------
  +-----J3-----+   pin 1    +12 VDC
  | 4  3  2  1 |   pin 2    +12 Volts Return
  +------------+   pin 3    + 5 Volts Return
                   pin 4    + 5 VDC



**********************************************************************
                      F   E   A   T   U   R   E  S
**********************************************************************
SEAGATE  ST31250/32550N/ND/W/WD/WC/DC INSTALL.GUIDE 83328920, REV. E

 Preface
 -------
 This manual contains information for users of the Seagate ST31250
 and ST32550 Barracuda 2LP SCSI disc drives. It provides support
 services, performance specifications, and initial setup information.
 Additional information is available in the Barracuda 2LP Product
 Manual (part number 83328930). Contact your Seagate sales
 representative if you need to order this publication.


 Electrostatic discharge protection
 ----------------------------------
 Caution.
 Removal of circuit boards by personnel not performing depot
 repair will damage components and may void the warranty.

 All drive electronic assemblies are sensitive to static electricity,
 due to the electrostatically sensitive devices used within the drive
 circuitry. Although some devices such as metaloxide semiconductors
 are extremely sensitive, all semiconductors, as well as some
 resistors and capacitors, may be damaged or degraded by exposure
 to static electricity.

 Electrostatic damage to electronic devices may be caused by the
 direct discharge of a charged conductor or by exposure to the
 static fields surrounding charged objects. To avoid damaging drive
 electronic assemblies, observe the following precautions when
 installing or servicing the drive:

 - Ground yourself to the drive whenever the drive electronics are
   or will be exposed. Connect yourself to ground with a wrist strap
   (Seagate part number 12263496). Connection may be made to any
   grounded metal assembly. As a general rule, remember that you and
   the drive electronics must all be grounded to avoid potentially
   damaging static discharges.

 - Turn off the power before removing or installing the DC power
   cable.

 - Do not remove any circuit boards from the drive.

 - Never use an ohmmeter on any circuit boards.

 - When installing the drive on a carrier or tray, discharge the
   static electricity from the carrier or tray prior to inserting it
   into the system.


 Important safety information and precautions
 --------------------------------------------
 Caution. Use forced-air ventilation when bench testing the drive to
 ensure proper cooling of drive components.

 Use proper safety and repair techniques for safe, reliable operation
 of this unit. Service should be done only by qualified persons.

 The procedures in this manual and labels on the unit contain warnings
 and cautions that must be carefully read and followed to minimize or
 eliminate the risk of personal injury. The warnings point out condi-
 tions or practices that may endanger you or others. The cautions
 point out conditions or practices that may damage the unit, possibly
 making it unsafe for use.

 Always observe the following warnings and precautions:

 - Perform all maintenance by following the procedures in this manual.

 - Follow all cautions and warnings in the procedures.

 - Use sound safety practices when operating or repairing the unit.

 - Use caution when troubleshooting a unit that has voltages present.
   Turn off power to the unit before servicing it.

 - Wear safety shoes when removing or replacing heavy parts.

 - Ensure that the internal temperature of the rack or cabinet does
   not exceed the limits defined for the drive when the drive is
   mounted in an equipment rack or cabinet. When units are stacked
   vertically, pay special attention to the top where temperatures
   are usually highest.

 - Do not remove any circuit boards from the drive chassis. Return
   the entire drive for depot repair if any circuit board is
   defective. Removal of circuit boards by personnel not performing
   depot repair will damage components and may void the warranty.

 - Do not remove the head and disc assembly (HDA) from the drive
   chassis. Return the entire drive for depot repair if the HDA is
   defective.

 - Do not attempt to disassemble the HDA. It is not field repairable.
   If the sealed HDA is opened by personnel not performing depot
   repair, this will damage compo-nents and void the warranty.

 As a component, this drive is designed to be installed and operated
 in accordance with UL1950, IEC950, EN60950, CSA C22.2 950, and
 VDE0805.

 Typical applications of these disc drives include customer packag-
 ing and subsystem design. Safety agencies conditionally certify
 component assemblies, such as the Barracuda disc drive, based on
 their final acceptability in the end-use product. The subsystem
 designers are responsible for meeting these conditions of accept-
 ability in obtaining safety, regulatory agency compliance in their
 end-use products and for certifying where required by law. A
 necessary part of meeting safety requirements is the provision
 for overcurrent protection on drive SELV supply voltages.

 This unit is a component part and as such is not meant to comply
 with FCC or similar national requirements as a standalone unit.
 Engineering radiated emissions test results are available through
 the Seagate Safety Department to assist the subsystem designer.


 General description
 -------------------
 Barracuda 2LP SCSI disc drives are high-speed, randomaccess digital-
 data storage devices.

 The drive is a component for installation in an enclosure designed
 for the drive. This is often a rack within the system or an external
 enclosure designed to house one or more disc drives or other
 peripheral units. In either case, the disc drive must receive
 adequate cooling and it must be sufficiently grounded and
 shielded from emissions. The Barracuda 2LP Product Manual (part
 number 83328930) contains guidelines for a properly designed
 enclosure.



**********************************************************************
                      G   E   N   E   R   A   L
**********************************************************************
SEAGATE   SCSI

 Interface requirements
 ----------------------
 How to use this interface manual

 This specification is designed to provide a universal detailed
 description of the SCSI interface for those disc drive products whose
 Product Manuals (Volume 1) do not contain the details of how the
 SCSI interface is implemented by that drive.

 Note: Volume 1 Product Manuals have tables in Section 11 that specify
 which SCSI-1 or SCSI-2/SCSI-3 features they implement, what the
 default parameters are for the various features they implement and
 which parameters are changeable and which are not. No method exists
 at present to inform an initiator if a target supports "SCSI-3"
 features as opposed to only SCSI-2 features. A few "SCSI-3" features
 are supported by Seagate drives, but no attempt has been made herein
 to differentiate between SCSI-2 and "SCSI-3" features. Therefore,
 when an Inquiry command reports what the ANSI approved version of the
 drive is, it reports either SCSI-1 or SCSI-2, where "SCSI-2" means
 SCSI-2 features plus some "SCSI-3" features.

 No attempt is made in this universal specification to specify which
 descriptions or tables apply to SCSI-1 and which to SCSI-2 or SCSI-3.
 The combination of this general specification with the details in
 the Section 11 tables of the individual drive Product Manual (Volume
 1) provides a description of the individual drive 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 Volume 2 of a set of manuals that is made up of
 separate drive Product Manuals (Volume 1) and this manual. This
 Volume 2 Manual is referenced by other Volume 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.


 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 above. The interface is compatible
 with the SCSI Interface Specifications of the ANSI SCSI-1 standard,
 the ANSI SCSI-2 Standard and the common command set (CCS) document,
 Revision 4.B. The disc drives covered by this Product Manual are
 classified as "Intelligent" peripherals.

 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 drivers and
 receivers or differential 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 drive model, the drive must act
 as an initiator, but does not otherwise do so. For purposes of this
 specification, "disc drive" may be substituted for the word "target"
 wherever "target" appears.


 GLOSSARY
 --------
 Arbitration - SCSI bus phase wherein SCSI devices try to gain control
 of the SCSI bus to operate as an initiator or target

 Byte - This term indicates an 8 bit hexadecimal construction.

 Command Descriptor Block (CDB) - The structure used to communicate
 requests from an initiator to a target.

 Connect - The function that occurs when an initiator selects a target
 to start an operation.

 Disconnect - The function that occurs when a target releases control
 of the SCSI bus, allowing it to go to the Bus Free phase.

 FRU (Field Replaceable Unit) - An assembly that is believed faulty
 based on test results. A value of 00h indicates an unknown cause or
 the end of a list of known possible causes. Nonzero values have
 product unique meanings.

 Initiator - A SCSI device (usually a host system) that requests an
 operation to be performed 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
 zero 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 following the successful receipt of one of the QUEUE
 messages. This relationship replaces the prior I T L nexus. (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


 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 (Volume 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.

 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.

 The Host Adapter/Initiator must be identified by one of the eight
 SCSI Device Addresses. Make sure that none of the devices on the SCSI
 bus have duplicate addresses. Certain SCSI bus functions are assigned
 to the initiator and certain SCSI bus functions are assigned to the
 target. The initiator will select a particular target. The target
 will request the transfer of Command, Data, Status or other
 information on the data bus.

 Information transfers on the data bus are interlocked and follow a
 defined REQ/ACK Handshake protocol. One byte of information will be
 transferred with each handshake. Synchronous data transfers do not
 require a one for one interlocking of REQ/ACK signals, but the total
 number of REQ pulses in a particular data transfer event must equal
 the total number of ACK pulses.

 The disc drive supports single initiator, single target; single
 initiator, multiple target; multiple initiator, single target; or
 multiple initiator, multiple target bus configurations.


 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 by a target to indicate whether
 Control or Data information is on the Data Bus. Assertion indicates
 Control.

 I/O (Input/Output) - A signal driven by a target to control the
 direction of data movement on the Data Bus with respect to an
 initiator. Assertion indicates input to the initiator. This signal
 also distinguishes between Selection and Reselection phases.

 MSG (Message) - A signal driven by a target during the Message phase.

 REQ (Request) - A signal driven by a target to indicate a request for

 REQ/ACK data transfer handshake.

 ACK (Acknowledge) - A signal driven by an initiator to indicate an
 acknowledgment for a REQ/ACK data transfer handshake.

 ATN (Attention) - A signal driven by an initiator to indicate the
 Attention condition. It is used to request to send a message out to
 the target. If an initiator asserts ATN while asserting SEL it
 indicates to the target that the initiator supports messages other
 than command complete.

 RST (Reset) - An "OR-tied" signal that indicates the Reset condition.

 DIFFSENS (Differential Sense) - When the drive has differential SCSI
 I/O circuits, the DIFFSENS signal disables the drive s differential
 driver/receiver circuits if the SCSI I/O cable is plugged in upside
 down, or if a single-ended SCSI I/O cable is plugged into a
 differential I/O drive. Disabling the differential I/O drivers/
 receivers is necessary to prevent burning 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 checks 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.


 Drive Select
 ------------
 For SCSI ID selection install drive select jumpers as shown in
 configuration selection figure in applicable Product Manual. Refer to
 section 10 of the individual drive Product Manual for the location
 of the drive select header. The disc drive using the eight bit data
 interface can have one of eight ID bits selected by installing 0 to 3
 jumpers in a binary coded configuration on the drive select header.
 Drives using the 16 bit data interface can have one of sixteen ID
 bits selected by installing 0 to 4 jumpers in a binary coded
 configuration on the drive select header.

 Signal Values
 -------------
 Signals may assume true or false values. There are two methods of
 driving these signals. In both cases, the signal shall be actively
 driven true, or asserted. In the case of OR-tied drivers, the driver
 does not drive the signal to the false state, rather the bias
 circuitry of the bus terminators pulls the signal false whenever it
 is released by the drivers at every SCSI device. If any driver is
 asserted, then the signal is true. In the case of non-OR-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.


 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
 several 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 driven false during the Arbitration phase. There is
 no operational problem in mixing OR-tied and non-OR-tied drivers on
 signals other than BSY and RST.


 Signal sources
 --------------
 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.


 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 delay. Then, except in certain single initiator
 environments with initiators employing the single initiator option
 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.


 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, 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 delays and release
 BSY. The initiator shall then wait at least a bus settle delay before
 looking for a response from the target.


 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 bus settle delay. The selected target will
 examine the Data Bus in order to determine the SCSI ID of the
 selecting initiator unless the initiator employed the single
 initiator option. The selected target shall then assert BSY within a
 selection abort 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 two
 deskew delays after the initiator detects BSY is asserted, it shall
 release SEL and may change the Data Bus.


 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 makes
 it impossible for the target to determine the initiator s SCSI ID.


 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.


 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 cable skew delay, 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 ACK 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.


 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. 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 ACK pulses by the
 REQ/ACK offset, the target shall not assert REQ until the next ACK
 pulse is received. 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 before asserting the
 ACK signal.


 Unit attention condition
 ------------------------
 The disc drive sets up the Unit Attention condition when it stores
 (within itself) a Unit Attention condition flag for each device on
 the SCSI bus having an initiator relationship with the disc drive,
 and this Unit Attention condition persists for each initiator until
 the condition is cleared (flag negated) by each initiator
 individually. The Unit Attention condition results when one of the
 following events occur:

  1. A power-on sequence occurs.
  2. A reset is generated internally by the disc drive (caused by a
     power glitch).
  3. A Bus Device Reset message causes the disc drive to reset itself.
  4. The RESET I/O line resets the disc drive.
  5. An initiator changes one or more of the Mode Select parameters in
     the disc drive (these changes could affect one or more of the
     other initiators).
  6. The inquiry data has been changed.
  7. The mode parameters in effect for an initiator have been restored
     from nonvolatile memory.
  8. An event occurs that requires the attention of the initiator.
  9. A Clear Queue message received.
 10. The Log parameters are changed. Unit Attention Condition is
     posted for all initiators in the system other than the one
     that changed the Log Parameters.

 The Unit Attention Parameters page (page 00h, bit 4 of byte 2) of the
 Mode Select Command controls whether or not a Check Condition Status
 is to be reported to affected initiators when a Unit Attention
 condition exists. The Unit Attention condition for a particular
 initiator is cleared when that initiator does one of the following:

 1. It sends a Request Sense Command.
 2. It sends any other legitimate command, with the exception
    of the Inquiry command. The Inquiry command does not clear the
    Unit Attention condition.

 When a Unit Attention condition flag is stored in the disc drive
 for an initiator, the commands that initiator issues to the disc
 drive operate as described in the following paragraphs.

 If an initiator sends an Inquiry command to the disc drive when the
 disc drive has stored a Unit Attention condition flag for that
 initiator before or after the disc drive reports Check Condition
 status), the disc drive shall perform the Inquiry command and shall
 not clear the Unit Attention condition.

 If an initiator sends a Request Sense command to the disc drive when
 a Unit Attention condition flag is stored for that initiator (before
 or after the disc drive reports Check Condition), the disc drive
 shall discard any pending sense data, report the Unit Attention Sense
 Key, and clear the Unit Attention condition (negate the flag) for
 that initiator.

 If an initiator issues a command other than Inquiry or Request Sense
 while a Unit Attention condition flag is stored for that initiator,
 the disc drive may or may not perform the command and report Check
 Condition status, depending on whether or not the Unit Attention bit
 is zero or one in the Unit Attention Mode Parameters page (Page 00h,
 bit 4 of byte 2). If a Request Sense is issued next, the Unit
 Attention condition is reported and cleared (flag negated) as noted
 in the preceding paragraph. If another command other than Request
 Sense or Inquiry is issued instead, the disc drive shall perform the
 command and return the appropriate status. The Unit Attention
 condition for the subject initiator is cleared (flag negated) and the
 sense data and flag indicating there has been a Unit Attention
 condition are lost.


