
S T 1 2 4 0 0 W    SEAGATE
NO MORE PRODUCED                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 3.5"/HH               Cylinders    2626|     |     |
Capacity form/unform  2148/ 2537 MB        Heads          19|     |     |
Seek time   / track   9.0/ 2.0 ms          Sector/track     |     |     |
Controller           SCSI2 SI/WI/FAST      Precompensation
Cache/Buffer           256 KB SEGMENTED    Landing Zone
Data transfer rate    4.000 MB/S int       Bytes/Sector      512
                     20.000 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     %         8 80    |      5 95
       standby            W     Altitude    km    -0.305  3.048| -0.305 12.192
       idle           9.0 W     Shock        g        10       |     60
       seek               W     Rotation   RPM      5411
       read/write         W     Acoustic   dBA
       spin-up            W     ECC        Bit   REED SOLOMON
                                MTBF         h     500000
                                Warranty Month        60
Lift/Lock/Park     YES          Certificates     CSA,EN60950,FCC,UL1950,VDE


**********************************************************************
                        L   A   Y   O   U   T
**********************************************************************
SEAGATE  ST12400W/WD PRODUCT MANUAL 77767457 REV. C 17/3/95

  +---------------------------------------------------------+
  |                                                         |XX1
  |                                                         |XXPower
  |                                                         |1-+
  |                                                         || J5
 ++LED                                                      || |
 ++                                                         |+-+
  |                                                         |+1+
  |                                                         ||X|I/O
  |                                                         ||X|
  |                                                         ||X|
  |                                                         ||X|J1
  |                                                         ||X|
  |+-+                                                      ||X|
  || |J6                                                    ||X|
  |+-1                                8--------1            ||X|
  |                                   +--------+J2          |+-+
  +---------------------------------------------------------+



**********************************************************************
                      J   U   M   P   E   R   S
**********************************************************************
SEAGATE  ST12400W/WD  PRODUCT MANUAL  77767457 REV. C  17/3/95

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



   REAR VIEW                             +------ 5V
                                         | +---- GND
     (TOP)                               | | +-- GND
      34                   1         1   | | | + 12V
      +---------------------+  +-J5---+ +-------+
  ----+|||||||||||||||||||||+--+::::::+-+O O O O+-
      +---------------------+  +------+ +-------+
      68pin I/O Cable           ||||||    Power   SCSI ID = 0 (none)
      Connection                |||||+----------- SCSI ID = 1
                                ||||+------------ SCSI ID = 2
                                |||+---------+--- SCSI ID = 4 or pin-6
                                |||          +--- REFIND+
                                ||+-------------- SCSI ID = 8
                                |+--------------- pin-10 GND
                                +---------------- pin-11 +5V

 J5  SCSI ID
 -----------
   +----------+-------------------------------+
   | SCSI ID  |       Jumper Location         |
   |          |             PINS              |
   |          |  7-8  |  5-6  |  3-4  |  1-2  |
   +----------+-------+-------+-------+-------+
   |    0     | OPEN  | OPEN  | OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    1     | OPEN  | OPEN  | OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |    2     | OPEN  | OPEN  | CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |    3     | OPEN  | OPEN  | CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |    4     | OPEN  | CLOSED| OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    5     | OPEN  | CLOSED| OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |    6     | OPEN  | CLOSED| CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |    7     | OPEN  | CLOSED| CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |    8     | CLOSED| OPEN  | OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    9     | CLOSED| OPEN  | OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |   10     | CLOSED| OPEN  | CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |   11     | CLOSED| OPEN  | CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |   12     | CLOSED| CLOSED| OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |   13     | CLOSED| CLOSED| OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |   14     | CLOSED| CLOSED| CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |   15     | CLOSED| CLOSED| CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+


 RIGHT SIDE VIEW

   +-J1                                  TOP (HDA)
   |X+------------+--------+-----PWA--------------------Front of drive
   +-+            |12345678|J2
                  +--------+
  +Terminator PWR -+||||||+- RESERVED
  +Terminator PWR --+||||+-- Start Delay (12 secs * ID)
  |  Enable T-Res ---+||+--- Motor Start
  | Parity Enable ----++---- Write Protect
  |
  |
  Terminator Power-source Table
  -----------------------------
  1 2             1 2             1 2
 +----           +----           +----
 |X o            |o X            |o o
 |X o            |o X            |xxx
 +------         +------         +-------
 Drive Supplies  Drive Supplies  Bus Supplies
 Bus             Own             Drive (Position A)


 FRONT VIEW                                   J6
                TOP (HDA)                  +-----1+
 -------PWA--------------------------------+::::::+---
              ++                           +------+  SCSI ID = 0 none
              ++LED            pin-11 +5V --+||||+-- SCSI ID = 1
                               pin-10 GND ---+||+--- SCSI ID = 2
                           SCSI ID = 8 or -+--++--+- SCSI ID = 4 or
                           pin-8 BUSY     -+      +- pin-6 REFIND+

 NOTE
 If these ID jumper are used, the ID jumpers J5 ARE NOT USED!!!!!

 J6  SCSI ID
 -----------
   +----------+-------------------------------+
   | SCSI ID  |       Jumper Location         |
   |          |             PINS              |
   |          |  7-8  |  5-6  |  3-4  |  1-2  |
   +----------+-------+-------+-------+-------+
   |    0     | OPEN  | OPEN  | OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    1     | OPEN  | OPEN  | OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |    2     | OPEN  | OPEN  | CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |    3     | OPEN  | OPEN  | CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |    4     | OPEN  | CLOSED| OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    5     | OPEN  | CLOSED| OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |    6     | OPEN  | CLOSED| CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |    7     | OPEN  | CLOSED| CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |    8     | CLOSED| OPEN  | OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |    9     | CLOSED| OPEN  | OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |   10     | CLOSED| OPEN  | CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |   11     | CLOSED| OPEN  | CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+
   |   12     | CLOSED| CLOSED| OPEN  | OPEN  |
   +----------+-------+-------+-------+-------+
   |   13     | CLOSED| CLOSED| OPEN  | CLOSED|
   +----------+-------+-------+-------+-------+
   |   14     | CLOSED| CLOSED| CLOSED| OPEN  |
   +----------+-------+-------+-------+-------+
   |   15     | CLOSED| CLOSED| CLOSED| CLOSED|
   +----------+-------+-------+-------+-------+


 Drive ID/option select header
 -----------------------------
 Both J1-auxiliary and J6 have pins for selecting drive ID and for
 connecting the synchronized spindle cable and the remote LED cable.
 Only one or the other should be used, although using both at the same
 time would not damage the drive. The notes ([1]-[9]) following the
 figures describe the functions of the various jumper positions on the
 three connectors J2, J1-auxiliary and J6. Sug-gested part number for
 the unusual J2 jumper is Molex 52747-0211 (Seagate P/N 77679052).

     Notes explaining the functions of the various jumpers on jumper
     header connectors J2, J1-auxiliary and J6 are given below in
     left to right order of jumper position. The term "default"
     means as standard OEM units are configured when shipped from
     factory. "Off" means no jumper is installed; "On" means a jumper
     is installed. "Off" or "On" underlined is factory default
     condition.

     The PCB on "WC" models does not have connector J1-auxiliary, but
     has a single 80 pin combined SCSI I/O and DC power connector
     instead of the pictured 68 pin SCSI I/O, J1-auxiliary and 4 pin
     DC power connectors. Included among the 80 pins are the SCSI ID,
     Motor Start and Delayed Motor Start select functions, and the
     synchronous spindle master sync signal (REFIND+) and the remote
     LED signals. Do not use J2 and J6 for these five functions if the
     host uses the ones included in the 80 pin connector.

     The drive uses headers J6 or J1-auxiliary for drive ID
     determination only during a 250 ms initialization period
     following power-on or after a drive reset. During this
     initialization period, the drive control logic connects pins
     2, 4, 6 and 8 to ground and checks the logic state of pins 1,
     3, 5 and 7. A ground on a pin 1, 3, 5, 7 indicates an asserted
     low state, while an open circuit, high impedance or +5 V
     indicates a negated high state. The drive user can install jumper
     plugs to connect pins 2, 4, 6 and 8 to pins 1, 3, 5 and 7,
     respectively, in the desired ID pattern.

     The drive only connects ground to pins 2, 4, 6 and 8 during the
     250 ms initialization period. The user may install a cable on J6
     or J1-auxiliary in order to connect the drive ID pattern to pins
     1, 3, 5 and 7 through some external switching circuit. The drive
     ID should be applied for at least the 250 ms period. During the
     remaining operational time of the drive, the drive does not poll
     pins 1, 3, 5 and 7 for drive ID, unless a reset occurs. See Note
     [4] for information on the use of pins 2, 4, 6 and 8 during
     non-initialization periods.

     During non-initialization periods when the drive does not connect
     ground to pins 2, 4, 6 and 8, these pins can be used for
     non-drive ID functions. Therefore, instead of using jumper plugs
     on J1-auxiliary to estab-lish drive ID, a cable can be connected
     to either J6 or J1-auxiliary to connect the drive activity (busy)
     LED and make parallel connections of pins 1, 3, 5 and 7 to
     external drive ID switching or jumpering circuits. If connected
     pin 8 lights the drive busy LED when the drive connects
     ground to that pin. Connection can be made to pin 6 to conduct
     the synchronized spindle reference signal, REFIND+ to the host
     and to other Seagate disk drives. Spindle synchronization
     typically works effectively only if all drives connected through
     pin 6 are identical in make and model. During the 250 ms
     initialization period the LED lights and the REFIND+ signal goes
     to 0 V.

     J6 can be used to establish drive ID using jumpers (or remote ID
     selector) and a cable can be plugged simultaneously to
     J1-auxiliary to connect to the drive activity (busy) LED and the
     synchronized spindle signal SSP. The vice-versa arrangement is
     possible also. Two separate drive ID determining locations should
     not be used, however.

     These jumper positions apply to model ST12400W only.

     This jumper position applies to models ST12400W and ST12400WD
     only.

     These signals are also on J1. The J2 and J6 jumper headers
     are not used if the J1 signals are used.

     Drive is probably shipped with this jumper installed, but it
     should be removed if the system uses REFIND+ on J1-37.

     These jumper positions do not apply to "WC" models.

 J2 Jumper
 Installation |Jumper Function Description
 -------------+----------------------------------------------------
 RES          |
 Off/On       |Reserved. Default is no jumper installed.
 -------------+----------------------------------------------------
 DS  ME       |
 Off Off      |Spindle starts immediately after power up - Default
              |setting.
 -------------+----------------------------------------------------
 Off  On      |Drive spindle does not start until Start Unit command
              |received from host.
 -------------+----------------------------------------------------
 On  Off      |Spindle Startup is delayed by SCSI ID times 12 seconds
              |after power is applied, i.e., drive 0 spindle starts
              |immediately when DC power connected, drive 1 starts
              |after 12 second delay, drive 2 starts after 24 second
              |delay, etc.
 -------------+----------------------------------------------------
 On  On       |Drive spindle starts when Start Unit command received
              |from host. Delayed start feature is overridden and does
              |not apply when ME jumper is installed.
              |
 -------------+----------------------------------------------------
 WP           |
 On           |Entire drive is write protected.
 -------------+----------------------------------------------------
 Off          |Drive is not write protected. Default is no WP jumper
              |installed.
              |
 PE           |
 On           |Parity checking and parity error reporting by the drive
              |is enabled. Default is PE jumper installed.
 -------------+----------------------------------------------------
 Off          |Drive does not report result of parity checking to
              |host.

 J2 Jumper
 Installation  Jumper Function Description
 TE (ST12400W only)
 On            With the jumper installed, the On-board (non-removable)
               terminator circuits are enabled (connected to the I/O
               lines). Default is jumper installed.
 Off           Terminator circuits not connected to I/O lines.

 TP  TP
 Off Off       No terminator power is connected to drive terminators
               or SCSI bus I/O pin 26.
 On  Off       Drive supplies its own terminator power only. Jumper on
               this position is factory default.
 Off On        Drive supplies power to I/O pin 26 of SCSI bus; none to
               internal terminators. When drives have differential I/O
               circuits, a jumper on the right TP position may be
               needed to power external terminators (see system
               documentation). The ST12400WD drive has differential
               I/O circuits which have no terminator circuits on the
               drive. The ST12400WC drive has no provisions for
               terminators and no provisions for terminator power in
               the 80 pin I/O connector. The TP jumpers do not apply
               to model ST12400WC.
 On  On        Drive supplies terminator power to itself (internal
               connection) and to I/O pin 26 of SCSI bus. This is a
               legal jumper setting.
 TP Position A
 On            This horizontally positioned jumper across the two
               TP positions nearest PCB edge, connects terminator
               power from SCSI bus I/O pin 26 to the drive's internal
               terminators (for Model ST12400W only).
 Off           See above explanations for TP jumpers.


 J1-Auxiliary,
 J6 Jumper
 Installation   Jumper Function Description
 A3 ,A2 ,A1 ,A0 Drive ID on SCSI Bus (J1-auxiliary or J6 may be
                used as the ID circuits are wired in parallel). The
                drive ID is binary coded positionwise i.e., jumper in
                position A3 is drive ID 8, A2 is drive ID 4, position
                A1 is ID 2, position A0 is ID 1 and no jumpers is ID
                0. Default is ID = 0. Both J1- auxiliary and J6 should
                not be used at the same time, because at some future
                time when the ID is changed the user could fail to
                configure both J1-auxiliary and J6 the same. Model
                ST12400WC does not have J1-auxiliary.

 SSP
 Used only as a cable connection for the reference index signal
 (REFIND+) (J1-6A and J6 Pin 6, bottom) for sync spindle feature.

 J1-10A or J6-10 provides ground. When no cable is connected, no
 jumpers should be installed. Factory default is no jumper installed.
 If a jumper is installed between pins 5 and 6 it will erroneously
 enable Drive ID bit A2.


 Synchronized spindles interface
 -------------------------------
 The Synchronized Spindles Interface (SSI) allows several drives
 operating from the same host to operate their spindles at a
 synchronized rotational rate. Spindle synchronization typically works
 effectively only if all drives connected to the REFIND+ signal are
 identical in make and model.


 Electrical description
 ----------------------
 The electrical interface consists of one digital TTL reference index
 signal and ground. The reference index signal (REFIND+) is an output
 if the drive is configured as a master and is an input otherwise. The
 reference index signal is connected from drive to drive in a
 daisychain fashion.


 Termination
 -----------
 The reference index signal (REFIND+) is terminated with a 2K ohm
 resistor. Each drive has a termination resistor located on the Main
 PCB. The terminator resistor is not removable and is always in the
 circuit.


 Physical interface
 ------------------
 They are 12 pin, 6 jumper position gold header type connectors. Pins
 6 and 10 are used for connecting the Reference Index signal from
 drive to drive. Pin 6 is REFIND+ and Pin 10 is ground. Either
 J1-auxiliary or J6 may be used. On "WC" models REFIND+ is J6-6 and on
 J1-37.



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                      I   N   S   T   A   L   L
**********************************************************************
SEAGATE  ST12400W/WD/WC  PRODUCT MANUAL 77767457 REV. C  17/03/1995

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

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

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

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


 Installation
 ------------
 The drive is designed, manufactured, and tested with a "Plug in and
 Play" installation philosophy. This philosophy minimizes the
 requirements for highly trained personnel to integrate the drive
 into the OEM's system, whether in a factory or field environment.

 The drive has been low level formatted at the factory and need not be
 reformatted.


 Service tools
 -------------
 No special tools are required for site installation or recommended
 for site maintenance. The depot repair philosophy of the drive
 precludes the necessity for special tools. Field repair of the drive
 is not practical since there are no user purchasable parts in the
 drive.


 Product Warranty
 ----------------
 Beginning on the date of shipment to customer and continuing for a
 period of five years, Seagate warrants that each product (including
 components and sub-assemblies) or spare part that fails to function
 properly under normal use due to defect in materials on workmanship
 or due to non conformance to the applicable specifications will be
 repaired or replaced, at Seagate's option and at no charge to
 customer, if returned by customer at customer's expense to Seagate's
 designated facility in accordance with Seagate's Warranty Procedure.
 Seagate will pay for transporting the repaired or replacement item to
 customer. For more detailed warranty information refer to the
 Standard terms and conditions of Purchase for Seagate products.


 Shock
 -----
 a. Operating
    The drive, as installed for normal operation, shall operate error
    free while subjected to intermittent shock not exceeding 10 g's at
    a maximum duration of 11 ms (half sinewave). Shock may be applied
    in the X, Y, or Z axis.

 b. Nonoperating
    The limits of nonoperating shock shall apply to all conditions of
    handling and transportation. This includes both isolated drives
    and integrated drives.

 The drive subjected to nonrepetitive shock not exceeding 60 g's at a
 maximum duration of 11 ms (half sinewave) shall not exhibit device
 damage or performance degradation. Shock may be applied in the X, Y,
 or Z axis.


 Cooling
 -------
 Cabinet cooling must be designed by the customer so that the ambient
 temperature immediately surrounding the drive will not exceed
 temperature conditions. Specific consideration should be given to
 make sure adequate air circulation is present around the PCBs to meet
 the requirements.


 Drive mounting
 --------------
 When mounting the drive using the bottom holes care must be taken to
 ensure that the drive is not physically distorted due to a stiff
 non-flat mounting surface. The allowable mounting surface stiffness
 is 80 lb/in (14.0 N/mm). The following equation and paragraph define
 the allowable mounting surface stiffness:

                      K*x = 80 lb (14.0 N)

 where 'k' represents the mounting surface stiffness (units of lb/in
 or N/mm), and, 'k' represents the out-of-plane mounting surface
 distortion (units of inches or millimetres). The out-of-plane
 distortion ('x') is deter-mined by defining a plane with three of the
 four mounting points fixed and evaluating the out-of-plane
 deflection of the fourth mounting point when a known force is
 applied to the fourth point.



 General cable characteristics
 -----------------------------
 In general, cables having the characteristic impedance's given above
 are not available; however, impedance's that are somewhat lower are
 satisfactory. A characteristic impedance of 100 ohm  10% is
 recommended for unshielded flat or twisted pair ribbon cable.
 However, most available cables have a somewhat lower characteristic
 impedance. To minimize discontinuities and signal reflections, cables
 of different impedance's should not be used in the same bus.

 Implementations may require tradeoffs in shielding effectiveness,
 cable length, the number of loads, transfer rates, and cost to
 achieve satisfactory system operation. If shielded and unshielded
 cables are mixed within the same SCSI bus, the effect of impedance
 mismatch must be carefully considered. Proper impedance matching is
 especially important in order to maintain adequate margin at FAST
 SCSI transfer rates.


 Cable for "W/WD" model drives
 -----------------------------
 Only nonshielded cable is applicable. A 68 conductor flat cable or
 two, 34 conductor cables shall be used. Conductors should be on 50
 (1.27 mm) mil centers to be used with connector. A minimum conductor
 size of 28 AWG should be used to minimize noise effects.

 Suggested nonshielded flat cable part numbers are:

 Flat cable - 35M-3365-68
 Twisted pair - Spectra Twist in flat 455-248-68
 Equivalent parts may be used.


 Cables for "WC" drive models
 ----------------------------
 The 80 pin connector option is intended for use on drives that plug
 directly into a wall or bracket mounted connector in the host
 equipment. Cable mounted connectors would not be used in such a case.
 Installations with cable mounted connectors are not recommended.


 Mating connectors for model ST12400W/WD
 ---------------------------------------
 The nonshielded cable connector shall be a 68 conductor connector
 consisting of two rows of 34 male contacts with adjacent contacts
 1.27 mm (0.050 inch) apart.

 Recommended Mating Connector Part Numbers for above flat cable are:

 Closed end       Amp Model 749925-5  (50 mil conductor centers for
 (for cable ends)                     28 or 30 AWG wire) This
                                      connector can only be used on
                                      cable ends.

 Open end         Amp limite 88-5870-294-5  W/O Strain Relief, (25 mil
                                            conductor centers, 30 AWG
                                            wire). Use either on cable
                                            ends or in cable middle
                                            section for daisychain
                                            installations.

 The disc drive device connector is a nonshielded 68 conductor
 connector consisting of two rows of 34 female pins with adjacent pins
 1.27 mm (0.050 inches) apart. The connector is keyed by means of its
 shape.


 Mating connectors for "WC" models
 ---------------------------------
 The non-shielded connector shall be an 80 conductor connector
 consisting of two rows of 40 contacts with adjacent contacts 50 mils
 (1.27 mm) apart. The connector is keyed by its shape.


 J2 Jumper plug part number
 --------------------------
 Option select header connector J2 on the PCB uses an unusual type of
 jumper, its part number is given here for reference:

                     Molex 52747-0211 (Seagate P/N 77670952).

 Recommended PCB or bulkhead mounted connectors are:

 Straight-in (most commonly used):   Right angle to PCB connector:
 Seagate P/N: 77678703               Seagate P/N: 77678559
 Amp US P/N: 2-557103-1              Amp US P/N: 2-557101-1
 Amp Japan P/N: 5-175475-9           Amp Japan P/N: 5-175474-9


 Grounding
 ---------
 Signal ground (PCBA) and HDA ground are connected together in the
 ST12400Wx drive and cannot be separated by the user. The equipment
 in which the drive i smounted is connected directly to the HDA and
 PCB with no electrically isolating shock mounts. If itis desired for
 the system chassis to not be connected to the HDA/PCBA ground, the
 systems integrator or user must provide a nonconductive (electrically
 isolating) method of mounting the drive in the host equipment.


 DC cable and connector
 ----------------------
 The model ST12400W/WD drive receives DC power through a 4 pin
 connector mounted at the rear of the main PCB. Recommended part
 numbers of the mating connector are listed below, but equivalent
 parts may be used.


 Mating connector parts
 ----------------------
 Type of cable        Connector      Contacts (20-14 AWG)
 14 AWG AMP           1-480424-0     AMP 60619-4 (Loose Piece)
                                     AMP 61117-4 (Strip)

 The model ST12400WC requires no extra DC power cable since both DC
 power and SCSI I/O signals are all in the single 80 pin connector.


 Physical characteristics
 ------------------------
 This section defines the connectors, cables, signals, terminators and
 bus timing needed to implement SCSI.


 Physical description
 --------------------
 The model W and WD drives may be daisychained together or with other
 compatible SCSI devices using a common cable. Both ends of the cable
 must be terminated. Model ST12400 wide drives do not have on-board
 terminator circuits. The ST12400WD drive implements differential
 drivers and receivers. The model ST12400W/WC drive implements single
 ended drivers and receivers. All signals are common between all SCSI
 devices. The drive may be daisychained only with SCSI devices having
 the same type drivers and receivers. Devices having single ended
 interface circuits cannot be on the same daisychain with devices
 having differential interface circuit. A maximum of 16 SCSI devices
 (including the Host) may be daisychained together. The SCSI Devices
 at both ends of the daisychain are to be terminated. Intermediate
 SCSI devices shall not be terminated. Remove or disable (whichever is
 applicable) the terminators. Do not remove the terminator power
 source selector jumper TP.

 "NC" model drives plug into PCB or bulkhead connectors in the Host.
 They may be connected in a daisy-chain by the host backplane wiring
 or PCB circuit runs that have adequate DC current carrying capacity
 to support the number of drives plugged into the PCB or bulkhead
 connectors. A single 80 pin I/O connector cannot support the DC
 current needs of several drives, so no daisy-chain cables should be
 used. A single drive connected via a cable to a host 80 pin I/O
 connector is not recommended.


 Single ended I/O circuits ("W" models)
 --------------------------------------
 The maximum total cable length for use with "W" model drives (single
 ended I/O driver and receiver circuits) shall be 6 metres (19.7 ft.)
 when operating at line data transfer rates of 5 MBytes/sec or less,
 and 3 metres (9.85 ft.) when operating at transfer rates greater than
 5 Mbytes/sec (FAST SCSI). A stub length of no more than 0.1 metre
 (0.33 ft.) is allowed off the mainline interconnection with any
 connected equipment. An ideal impedance match with cable terminators
 implies a cable characteristic impedance of 132 ohms.


 Differential I/O circuits ("WD" models)
 ---------------------------------------
 The maximum total cable length for use with drives having
 differential I/O drivers and receiver circuits shall be 25 metres (82
 ft.). A stub length of no more than 0.2 metre (0.66 ft.) is allowed
 off the mainline interconnec-tion with any connected equipment. An
 ideal impedance match with cable terminators implies a cable
 characteristic impedance of 122 ohms.



**********************************************************************
                      F   E   A   T   U   R   E  S
**********************************************************************
SEAGATE  ST12400W/WC/WD  PRODUCT MANUAL 77767457  REV. C  17/3/1995

 Scope
 -----
 This specification describes the Seagate Technology, Inc. Hawk 2
 family Model ST12400 Wide SCSI bus Disc Drive. This high capacity,
 high performance member of the Seagate 3.5 inch rigid disc family
 has a new HDA (Head/Disc Assembly) design having improvements over
 previous 3.5-inch Seagate models. It has an embedded SCSI controller.
 The Model Hawk 2 Family (Wide bus) drive interface is defined for
 functional compatibility to a subset of the Seagate SCSI-2/SCSI-3
 Interface Specification 77738479, and the ANSI SCSI-2/SCSI-3
 standards. The Model Hawk 2 Family (Wide bus) drives are classified
 as "Intelligent" peripherals. The Hawk 2 Family (Wide bus) provides
 Level 2 conformance (highest level) with the ANSI SCSI-1 standard.


 General description
 -------------------
 The drives are a member of a family of low cost, high performance,
 highly reliable, random access storage devices designed to meet the
 needs of the OEM marketplace.

 The drive records and recovers data on 3.7 inch (95 mm) fixed discs.

 The drive supports the Small Computer System Interface (SCSI-1,
 SCSI-2 and SCSI-3) as described in the ANSI SCSI Interface
 Specifications to the extent described in this product specification
 (Volume 1). This manual defines the product performance
 characteristics of the ST12400 wide family of drives, together with
 the SCSI-2/SCSI-3 Interface Product Manual P/N 77738479 (Vol. 2,
 Version 2) which describes the general interface characteristics of
 this and other families of Seagate 3.5-inch drives.

 The drive interface supports multiple initiators, disconnect/
 reconnect, self configuring host software and automatic features
 that relieve the host from the necessity of knowing the physical
 characteristics of the targets (logical block addressing is used).

 The Head/Disc Assembly (HDA) is environmentally sealed at the
 factory. Air recirculates within the HDA through a nonreplaceable
 filter to maintain a contamination free head/disc environment.
 NEVER disassemble the Head/Disc Assembly (HDA). This exploded view is
 for information only. Do not attempt to service items in the sealed
 environmental enclosure (heads, media, actuator, etc.) as this
 requires special facilities. The drive contains no parts replaceable
 by the user. The drive warranty is voided if the HDA is opened.

 The ST12400 wide family drives use a dedicated landing zone at the
 innermost radius of the media to eliminate the possibility of
 destroying or degrading data by landing in the data zone. The drive
 automatically goes to the landing zone when the power is removed.

 The ST12400 wide family drives incorporate an automatic shipping lock
 which prevents potential damage to the heads and discs that result
 from movement during shipping and handling. The shipping lock
 disengages when power is applied to the drive and the head load
 process begins.

 The ST12400 wide family drives decode Track 0 location from the
 dedicated servo surface to eliminate mechanical transducer
 adjustments and related reliability concerns.

 The ST12400 wide family drives use a high performance actuator
 assembly that consists of a low inertia, balanced, patented, straight
 arm design that provides excellent performance with minimum power
 dissipation.


 Optional accessories (user installed)
 -------------------------------------
 The following accessories are available. All kits may be installed in
 the field.

 - Front Panel Kit (with green LED)

 - Single Unit shipping pack kit

 - Installation Guide P/N 77767465

 - Adapter Accessory Frame Kit P/N 75790701 (adapts 3.5-inch
   ST12400W/WD drive to fit in 5.25-inch drive mounting space, does
   not work for model ST12400WC).


 Prefetch/multi-segmented cache control
 --------------------------------------
 The drive provides prefetch (read look-ahead) and multi-segmented
 cache control algorithms that in many cases can enhance system
 performance. "Cache" as used herein refers to the drive buffer
 storage space when it is used in "cache" operations. To select
 prefetch and cache features the host sends the Mode Select command
 with the proper values in the applicable bytes in Mode Page 08h*.

 Prefetch and cache operation are independent features from the
 standpoint that each is enabled and disabled independently via the
 Mode Select command.


 Cache operation
 ---------------
 In general, 240 kBytes of the 256 kBytes of physical buffer space in
 the drive can be used as storage space for cache operations (984 KB
 of 1 MB for drives having 1 MB optional buffer). The buffer can be
 divided into logical segments (Mode Select Page 08h, byte 13) from
 which data is read and to which data is written. The drive maintains
 a table of logical block disk medium addresses of the data stored in
 each segment of the buffer. If cache operation is enabled (RCD bit =
 0 in Mode Page 08h, byte 2, bit 0. See SCSI Interface Product
 Manual), data requested by the host with a Read command is retrieved
 from the buffer (if it is there), before any disc access is
 initiated. If cache operation is not enabled, the buffer (still
 segmented with required number of segments) is still used, but only
 as circular buffer segments during disc medium read operations
 (disregarding Prefetch operation for the moment). That is, the drive
 does not check in the buffer segments for the requested read data,
 but goes directly to the medium to retrieve it. The retrieved data
 merely passes through some buffer segment on the way to the host. All
 data transfers to the host are in accordance with "buffer-full" ratio
 rules. See explanations associated with Mode page 02h (disconnect/
 reconnect control) in the SCSI Interface Product Manual.


 Caching write data
 ------------------
 Write caching is a write operation by the drive that makes use of a
 drive buffer storage area where the data to be written to the medium
 is stored in one or more segments while the drive performs the write
 command.

 Write caching is enabled along with read caching. For write caching,
 the same buffer space and segmentation is used as set up for read
 functions. The buffer segmentation scheme is set up or changed
 independently, having nothing to do with whether or not read and
 write caching is enabled or disabled. When a write command is issued,
 the cache is first checked to see if any logical blocks that are to
 be written are already stored in the cache from a previous read or
 write command. If there are, the respective cache segments are
 cleared. The new data is cached for subsequent Read commands.
 If the number of write data logical blocks exceeds the size of the
 segment being written into when the end of the segment is reached,
 the data is written into the beginning of the same cache segment,
 overwriting the data that was written there at the beginning of the
 operation. However, the drive does not overwrite data that has not
 yet been written to the medium.


 Synchronized spindle operation
 ------------------------------
 The synchronized spindles operation allows several drives operating
 from the same host to operate their spindles at the same synchronized
 rotational rate. Drives operating in a system in synchronized mode
 can increase the system capacity and transfer rate in a cost
 effective manner.

 For "W" and "WD" models the interface consists of a twisted pair
 cable that connects the drives in the synchronized system in a
 daisy-chain configuration. For "WC" models the reference index signal
 ("SYNC") signal is on pin J1-37 of the 80-pin I/O connector.

 Master/Slave operation is autoarbitrated by each drive after head
 load. Alternatively, each drive in the system can be configured by
 the host (using the Mode Select command Rigid Disc Drive Geometry
 page) to operate in either the master or slave mode.

 After loading heads, a drive autoarbitrates for occurences of the
 Reference Index Signal (REFIND+). If the drive detects no REFIND+
 signal on the line, it assumes master status and begins generating
 the REFIND+ signal. This signal will not be visible on the line until
 the last drive has powered up, since any unpowered drive holds the
 line low.

 Using Mode Select command, drives can be re-configured by the host to
 be master or slave any time after the last drive has powered up. The
 master provides the reference signal to which all other drives phase
 lock, including the master. The master can be a drive or the host
 computer. All the drives may be configured as slaves, allowing the
 host to provide the REFIND+ signal. All drives default to the
 synchronized mode when powered up, unless J6 pins 5 and 6 are
 jumpered.

 Each drive can be configured (jumpered) for the non-synchronized mode
 in which it ignores any reference signal that might be present. The
 connection of the synchronized reference signal to the host is
 required only if the host is to provide the reference signal. If the
 host does not provide the reference signal, the host should not be
 connected.


 Media description
 -----------------
 The media used on the drive has a diameter of approximately 95 mm
 (approximately 3.7 inches). The aluminum substrate is coated with a
 thin film magnetic material and overcoated with a proprietary
 protective layer for improved durability and environmental
 protection.


 Defect and error management
 ---------------------------
 The drive, as delivered, complies with this specification. The read
 error rate and specified storage capacity are not dependent upon use
 of defect management routines by the host (initiator).
 Defect and error management in the SCSI system involves the drive
 internal defect/error management and SCSI systems error
 considerations (errors in communications between Initiator and the
 drive). Tools for use in designing a defect/error management plan are
 briefly outlined in this section, with references to other sections
 where further details are given.


 Drive internal defects/errors
 -----------------------------
 Identified defects are recorded on the drive defects list tracks
 (referred to as the primary or ETF defect list). These known defects
 are reallocated during the initial drive format operation at the
 factory. Data correction by ECC can be applied to recover data from
 additional flaws if they occur.


 SCSI systems error considerations
 --------------------------------*
 Information on the reporting of operational errors or faults across
 the interface is given in SCSI Interface Product Manual. Message
 Protocol System is described in the SCSI Interface Product Manual.
 Several of the messages are used in the SCSI systems error management
 system. The Request Sense command returns information to the host
 about numerous kinds of errors or faults. The Receive Diagnostic
 Results reports the results of diagnostic operations performed by the
 drive.

 Status returned by the drive to the Initiator is described in the
 SCSI Interface Manual. Status reporting plays a role in the SCSI
 systems error management and its use in that respect is described in
 sections where the various commands are discussed.


 Electrical description
 ----------------------
 The ST12400W/WC models use single ended interface signals. These
 signals must be terminated with 110 ohm active termination circuits
 at each end of the total cable. ST12400WC drives have no provisions
 for terminators on the PCB. On model ST12400WC some method of
 external termination must be provided by the user, systems integrator
 or the host equipment manufacturer. On ST12400W drives terminator
 power can be supplied from the drive to the I/O connector by the
 drive by properly positioning the TP jumper plug and the J2 option
 select header. Single Ended circuits use open collector or three
 state drivers.

 The model ST12400WD uses differential interface signals and each of
 these must be terminated at each end of the total cable with 330 ohms
 to +5 V and 330 ohms to ground with 150 ohms between each
 differential pair. All I/O circuits are open collector, three state
 drivers. ST12400WD drives have no provisions for adding terminators
 on the PCB. Some method of external termination must be provided
 (where needed) by the user, systems integrator or host equipment
 manufacturer. The ST12400WD model drive can furnish terminator power
 to the SCSI I/O cable by properly positioning jumper plug TP.


 Single ended drivers/receivers
 ------------------------------
 Transmitter characteristics
 Single ended drives use an ANSI SCSI compatible open collector single
 ended driver. This driver is capable of sinking a current of 48 mA
 with a low level output voltage of 0.4 volt.

 Receiver characteristics
 Single ended drives use an ANSI SCSI single ended receiver with
 hysteresis gate or equivalent as a line receiver.


 Differential drivers/receivers
 ------------------------------
 The drive has no provisions for terminator circuits on the drives.

 Differential signals
 All differential interface signals consist of two lines denoted
 +SIGNAL and -SIGNAL. A signal is true when +SIGNAL is more positive
 than -SIGNAL, and a signal is false when -SIGNAL is more positive
 than +SIGNAL. All assigned signals shall be terminated at each end
 of the cable. Drive user, systems integrator or OEM manufacturer must
 provide some external means of termination. Terminator power can be
 supplied by the drive to the I/O cable by properly positioning a
 jumper plug.

 Output characteristics
 Each signal driven by differential interface drives shall have the
 following output characteristics when measured at the disc drive
 SCSI connector:

 Low-level output voltage* = 2.0 V maximum at
 Low-level output current  = 55 milliamps.
 High-level output voltage* = 3.0 V minimum at
 High-level output current  = -55 milliamps
 Differential voltage = 1.0V minimum with common-mode voltage ranges
                        from -7 V dc to +12 V dc.

 These voltages shall be measured between the output terminal and the
 SCSI device's logic ground reference.

 The output characteristics shall additionally conform to EIA
 RS-485-1983.

 Input characteristics
 Each signal received by differential interface drives shall have the
 following input characteristics when measured at the disc drive SCSI
 connector:

 Input current on either input = +2.0 milliamps maximum (includes both
                                 receivers and passive drivers).

 This requirement shall be met with the input voltage varying between
 -7 V dc and +12 V dc, with power on or off, and with the hysteresis
 equaling 35 mv, minimum.

 The input characteristics shall additionally conform to EIA
 RS-485-1983.


 Terminator requirements
 -----------------------
 Drive I/O termination is not provided internally on ST12400WD or
 ST12400WC drives. Terminator circuits, must be provided in some
 manner external to the ST12400WD/WC drives by the user, systems
 integrator or OEM manufacturer. It is highly recommended that ANSI
 SCSI-2 Standard's Alternative 2 termination (active termination) be
 used for single-ended ST12400W and ST12400WC applications, especially
 if the bus will be operated at transfer rates above 5 Mbytes/sec. The
 ST12400W provides on-board active termination that can be disabled by
 removal of the enable jumper TE. Power for the external terminators
 may be taken from the drive by installing a jumper plug on one of the
 J2-TP. If the TP jumper is not installed terminator power must be
 supplied by some other source. All single initiator/single target
 (nondaisychain) applications require that the Initiator and disc
 drive be terminated. Daisychain applications require that only the
 units at each end of the daisychain be terminated. All other
 peripherals on the chain should not be terminated.

 Note. Where terminators are not required, remove external terminator
       modules or disable terminators on the model ST12400W by
       removing the TE jumper from header J2. Removal of terminator
       power source selection jumper TP does not disconnect the
       terminators from the circuit.

 Note. ACTIVE TERMINATORS ARE HIGHLY RECOMMENDED FOR USE IN THE
       DAISYCHAIN AS DESCRIBED ABOVE. ACTIVE AND PASSIVE TERMINATORS
       SHOULD NOT BE MIXED ON THE SAME SCSI BUS.


 Terminator power
 ----------------
 The model ST12400W/WD drives may be configured to provide terminator
 power via pins 17, 18, 51 and 52 of the SCSI Bus, to supply power to
 the SCSI bus. The drive can provide power both to external
 terminators at the drive end and to the SCSI Bus terminator power
 lines to provide power for terminators at the other end of the I/O
 cable.

 SCSI devices providing terminator power (TERMPWR) shall have the
 following characteristics:

 V TERM = 4.50V to 5.25V
 800 mA min source drive capability
 1.0 A maximum

 The model ST12400WC drive cannot furnish terminator power, because no
 pins in the 80 pin I/O connector are devoted to terminator power.


 Options
 -------
 All options are incorporated or packaged at the manufacturing
 facility.


 Front panel
 -----------
 The normal front panel available is black plastic. Other panel colors
 may be special ordered. Each panel has a single rectangular green LED
 indicator lens which, when glowing, indicates the drive is selected.



**********************************************************************
                      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.


