
S T 3 6 1 0 N D    SEAGATE
NO MORE PRODUCED                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 3.5"/SLIMLINE         Cylinders    1872|     |     |
Capacity form/unform   535/  635 MB        Heads           7|     |     |
Seek time   / track  11.0/ 2.0 ms          Sector/track     |     |     |
Controller           SCSI2 DI/FAST         Precompensation
Cache/Buffer           256 KB              Landing Zone
Data transfer rate    4.000 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           6.5 W     Shock        g        10       |     75
       seek           7.0 W     Rotation   RPM      5411
       read/write         W     Acoustic   dBA
       spin-up            W     ECC        Bit
                                MTBF         h     200000
                                Warranty Month        24
Lift/Lock/Park     YES          Certificates     CSA,FCC,IEC950,UL1950,VDE


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SEAGATE  ST3600N/ND FAMILY INSTALLATION GUIDE 77738481, REV. A

  +---------------------------------------------------------+
  |1-+                                      +------1 J5     |XX
  || |J6                                    +------+        |XX SCSI
  |+-+                                                  +1  |XX I/O
  |                                                     ||  |XX
  |                                                     ||  |XX
  |                                          I/O        ++  |XX
  |                                          Terminators++  |XX
  |                                                     ||  |XX
  |                                                     ||  |XX
  |                                                     ++  |XX
  |                                                     ++  |XX
  |                                                     ||  |XX
  |                                                     ||  |XX
  |                                                     ++  |X1
  |                                                         |
  |                               +---------1 J2            |XX Power
  |                               +---------+               |XX
  +---------------------------------------------------------+



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                      J   U   M   P   E   R   S
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SEAGATE  ST3600N/ND FAMILY  INSTALLATION GUIDE 77738481, REV. A

 Jumper setting
 ==============

 Each disk drive has one or more option select header connectors on
 the back, side or front where jumper plugs are installed to select
 the way that the drive is to be configured or to select its ID on the
 I/O bus.


 J2  Motor Start/Write Protect/Terminator Power
 ----------------------------------------------

          +-1--2--3--4--5--6--7--8-+
          | o  X  o  o  o  o  o  1 |
          | o  X  o  o  o  o  xxxx |
          +----+-------------------+ \ Position A
              Position 2

     1   for Factory use only.

     2   Jumper installed in position 2 enables the Delayed Motor
         Start option (if jumper in position 3 is off). Motor start
         delays is 12 times the drive ID number in seconds; i.e. drive
         ID 0 starts immediately. drive one starts 12 seconds later,
         etc.
         Not factory installed.

     3   Jumper installed enables Motor Start option. The drive waits
         for the Start unit command from the host before starting the
         spindle motor. If no jumper is installed, drive operation de-
         pends on wether or not there is a jumper in position 2.
         Not factory installed.

         If jumpers 2 and 3 are both off, drive spins up with no delay
         when power is applied.

     4   Jumper installed means entire drive is write protected.
         Not factory installed.

     5   Jumper installed means parity checking by the drive is
         enabled.
         Not factory installed.

     6   Reserved for later use.

     7   Select terminator power source. In position 8 the drive
     8   supplies power to the SCSI bus, pin 26. In position 7 drive
         supplies power only to its own terminators. (Factory setting)
         Jumper horizontally between positions 7 and 8 (position A)
         means the drive takes power from the SCSI bus, pin 26.
         Jumpers installed on both 7 and 8 at same time is allowed.
         Default is jumper on position 7.


 J5 SCSI ID
 ----------
           SCSI ID 0        SCSI ID 1        SCSI ID 2
          +---------+      +---------+      +---------+
          | o  o  1 |      | X  o  o |      | o  X  o |
          | o  o  o |      | X  o  o |      | o  X  o |
        A +-0--1--2-+      +---------+      +---------+

           SCSI ID 3        SCSI ID 4        SCSI ID 5
          +---------+      +---------+      +---------+
          | X  X  o |      | o  o  X |      | X  o  X |
          | X  X  o |      | o  o  X |      | X  o  X |
          +---------+      +---------+      +---------+

           SCSI ID 6        SCSI ID 7
          +---------+      +---------+
          | o  X  X |      | X  X  X |
          | o  X  X |      | X  X  X |
          +---------+      +---------+

 Drive ID on SCSI Bus (J6 may be used instead). The drive ID is binary
 coded positionwise.


 J6 SCSI ID (optional)
 ---------------------

       A  A  A                         SCSI ID 0
     +-2--1--0----------+             +------------------+
     | o  o  o  o  o  1 |             | o  o  o  o  o  o |
     | o  o  o  o  o  o |             | o  o  o  o  o  o |
     +-1--2--3--4--5--6-+             +------------------+

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

      SCSI ID 3                        SCSI ID 4
     +------------------+             +------------------+
     | o  X  X  o  o  o |             | X  o  o  o  o  o |
     | o  X  X  o  o  o |             | X  o  o  o  o  o |
     +------------------+             +------------------+

      SCSI ID 5                        SCSI ID 6
     +------------------+             +------------------+
     | X  o  X  o  o  o |             | X  X  o  o  o  o |
     | X  o  X  o  o  o |             | X  X  o  o  o  o |
     +------------------+             +------------------+


      SCSI ID 7                        Sync Spindle
     +------------------+             +------------------+
     | X  X  X  o  o  o |             | o  o  o  X  o  o |
     | X  X  X  o  o  o |             | o  o  o  X  o  o |
     +------------------+             +------------------+


      Remote LED
     +------------------+
     | o  o  o  o  X  o |
     | o  o  o  o  X  o |
     +------------------+

 1,2,3  Either J5 or J6 (optional) may be used to select drive ID.
        Both should not be used at same time, because at some future
        time, settings may be changed, causing the drive to not
        respond correctly. The factory installs no ID jumpers on J5 or
        J6 (drive ID 0).

     4  Used as a cable connection for the Ref Index/+L signal for
        sync spindle feature.

     5  Used if needed for a connection to a remote LED indicator.
        Pin 10 (lower row), connects in the drive to the +5 V supply.
        Pin 9 (closest to drive HDA), connects in the drive to ground.

     6  Reserved.


 On SCSI I/O drives either J6 (on the front of the drive) or J5 (on
 the side behind the DC Power connector) may be used to set the drive
 ID. To avoid possible incorrect ID setting, do not use both J5 and
 J6 for ID selection.



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SEAGATE  ST3600 FAMILY  INSTALLATION GUIDE 77738481, REV. A

 Installation
 ============

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

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

 The drive may be mounted in any orientation.

 Mount to host system chassis using four 6-32 UNC screws. Three
 mounting holes are in each side and four in the bottom of the drive.
 The maximum length that the screws should extend into the side
 chassis mounting holes is 0.15 inch (3.81 mm), and 0.20 inch (5.1 mm)
 into bottom holes, measured from the outer surfce of the chassis.
 Tighten the screws down evenly to approximately 8 inch-Ibl. Do not
 over tigthen or force when screw does not seem to screw in easily
 (threads not correctly engaged).

 Verify that all connections between the drive and the host system are
 correctly installed. Most cables have a contrasting color stripe
 indicating pin 1.

 The disc drive(s) are to be installed in a customer supplied
 enclosure where the surrounding air does not exceed 50* C.


 Grounding
 ---------
 Signal ground (PCB) and HDA ground are connected together in the
 ST3600 drive and cannot be separated by the user. The equipment in
 which the drive is mounted is connected directly to the HDA and PCB
 with no electrically isolating shock mounts. If it is desired for the
 system chassis to not be connected to the HDA/PCB ground, the systems
 integrator or user must provide a nonconductive (electrically
 isolating) method of mounting the drive in the host equipment.


 SCSI interface cable connection
 -------------------------------
 Models ST3600N/ND are SCSI interface drives. System connection is
 via a 50-pin SCSI connector. Some cables have a contrasting color
 stripe on one edge to indicate pin 1. Strain relief is recommended
 at the cable. Do not block system cooling air flow in routing of
 cables.


 AT (IDE) interface cable connection
 -----------------------------------
 Model ST3600A Family drives AT (IDE) interface drive. System
 connection is via a 40 pin AT (IDE) connector. Some cables have a
 contrasting color strip on one edge to indicate pin 1. Use a strain
 relief device at the cable. Do not block system cooling air with the
 routing of cables.

 Connect the AT (IDE) I/O connector cable end to drive 0 (master) and
 if there is a drive 1 (slave) connect it to the connector in the
 middle of the cable.

 Order of locating the drives in the daisychain is not as important as
 getting proper drive ID set up for the drives intended for drive 0
 and drive 1.


 DC Power connection
 -------------------
 The drive receives DC power through a 4 pin connector mounted on the
 PCB next to the SCSI or AT (IDE) I/O connector.

 Pin 1    +12 V
     2    +12 V Return
     3    + 5 V Return
     4    + 5 V


 SCSI Resistor terminator packs
 ------------------------------
 If you are installing a single drive, the resistor terminator packs
 must remain installed. If you are installing multiple hard disc
 drives, remove the resistor termination packs from all the drives but
 the one connected to the end of the SCSI I/O cable.

 When reinstalling a resisor pack, note that pin 1 end on the pack is
 denoted by a dot, a number one or a notch. Usually, a square pad on
 the disc drive printed wiring assembly indicates pin 1 at the socket.

 Model numbers that end in "ND" have differential I/O circuits and
 these drives have no provisions for terminators that plug into the
 drive PCB. The system manufacturer must provide some external means
 of I/O line termination.

 The AT (IDE) interface drives have permanent internal I/O line
 termination and do not have removable terminators.



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                      F   E   A   T   U   R   E  S
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SEAGATE  ST3600 FAMILY  INSTALLATION GUIDE 77738481, REV. A

 Electromagnetic interference (EMI) considerations
 -------------------------------------------------
 The drive(s) described herein, as delivered, are designed for system
 integration and installing into a suitable enclosure prior to use.
 As such, the drive(s) described herein are supplied as a sub-assembly
 and are not subject to Subpart J of Part 15 of the FCC Rules and
 Regulations nor the radio Interference Regulations of the Canadian
 Department of Communications.

 However, the unit has been tested using proper shielding and ground-
 ing and found to be compliant with the Class A limits of the FCC
 Rules and the Regulations of the Canadian Department of
 Communications.

 Safety instructions
 -------------------
 The power supply must satisfy the safety requirements for SELV
 (Safety Extra Low Voltage) circuits.

 The incorporation of the disc drives listed in this guide into a
 customer enclosure must meet the appropriate safety requirements of
 the country in which it is used (e.g. UL 1950, CAN/CSA-C22.2 No. 950-
 M89, DIN VDE 0805/05.90 and EN 60950:1988 (IEC 950).


 Low Level formatting
 --------------------
 All ST3600 family drive models are low-level formatted at the factory
 and do not require this step during installation. If an installed
 drive is low-level formatted, all user data will be lost.


 Partitioning and high level formatting
 --------------------------------------
 A drive can be sub-divided into "partitions" which behave as
 individual drives within the system.


 Read/Write head auto-park
 -------------------------
 Seagate disc drives described herein mentioned in this drive park the
 heads automatically at power off. This feature requires no operator
 intervention.


 Write precompensation and reduced write current
 -----------------------------------------------
 Not required on Seagate SCSI or AT (IDE) interface drives covered by
 this manual.


 SCSI interface drives
 ---------------------
 The SCSI interface handles both drive geometry and defect management
 internally. In AT systems a drive type of zero, or the "no drive
 installed" option is selected for systems with SCSI drives.

 All SCSI interface drives are low-level formatted at the factory. You
 may wish to low-level format the drive to optimize performance for
 your system. Consult the controller documentation for information on
 low-level formatting. Partitioning and high-level formatting can be
 done through DOS by way of the FDISK utility for partiioning, and
 FORMAT for high-level formatting.


 AT (IDE) interface drives
 -------------------------
 Seagate AT interface drives mimic (translate) other drive geometries.
 If none of the drive types offered by the CMOS supports the number of
 heads, cylinders and sectors shown by the table, and your system
 does not support a "user-defined" drive type, then select a drive
 type in your system CMOS with a capacity which is less than or
 equal to the capacity given in the "MBytes" section of the table.

 Model       MBytes (F)    Cylinders   R/W Heads    Sectors/Track
 ST3600A     528           1024        16           63
 ST3500A     426            895        15           62

 When specifying drive geometry to the systems CMOS different values
 may be used for the Cylinders, Read/Write Heads and Sectors/Track
 than those given below. However, the final drive capacity shown by
 the CMOS cannot exceed the capacity shown in the MBytes column of the
 table.

 If your BIOS offers a "custom drive" or a "user-defined" drive type,
 use one of the configurations listed in the previous table.

 The CMOS calculation of drive capacity is based on a variation of the
 number of bits in a megabyte, for purposes related to hexadecimal
 addressing. When the drive geometry has been entered into the "user
 defined" or "custom" drive type. This number should correspond with
 the capacity listed in the MBytes column of the table.

 Note that the drive will provide the user with full capacity as
 specified in the MBytes (F) column of the table. The drive capacity
 can be verified by using the CHKDSK utility provided with DOS after
 the high-level formatting has been completed.



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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.


