S T 3 6 5 5 N SEAGATE NO MORE PRODUCED Native| Translation ------+-----+-----+----- Form 3.5"/SLIMLINE Cylinders 2676| | | Capacity form/unform 545/ MB Heads 5| | | Seek time / track 12.0/ 4.0 ms Sector/track | | | Controller SCSI2 SI/FAST Precompensation Cache/Buffer 256 KB SEGMENTED Landing Zone Data transfer rate 3.000 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 55 | -40 70 Power: sleep 0.9 W Humidity % | standby W Altitude km | idle 3.2 W Shock g | seek 5.6 W Rotation RPM 4500 read/write 5.4 W Acoustic dBA spin-up W ECC Bit MTBF h 250000 Warranty Month 24 Lift/Lock/Park YES Certificates CSA,FCC,TUV,UL1950,VDE
SEAGATE ST3390N/ST3655N PRODUCT MANUAL 36224-001, REV. A, 7/21/93
+---------------------------------------------------------+ | +----J5 |XX | +----+ |XX | ++ |XX | || |XX | || |XX | 1++ |XX | ++ |XX | Terminator || |XX |+--J12 Resistor || |XX || | Packs 1++ |XX J4 || | ++ |XX I/O |+--+ || |XX |+--J8 || |X1 || | 1++ | || | |XX || | J9+------+ +--+J6 |XX Power |+--+ +------+ +--+ |XX J3 +---------------------------------------------------------+
SEAGATE ST3390N/3655N PRODUCT MANUAL 36224-001, REV. A, 7/21/93
J3 DC Power and Pin Connector Assignment
+------------+ | 1 2 3 4 | +-+--+--+--+-+ | | | +----- + 5 VDC | | +-------- + 5 Volts Return | +----------- +12 Volts Return +-------------- +12 VDC
J5 SCSI ID Address Jumper Block
Ground+-2--4--6-+--- --+---------+--Circuit board MSB | o o o | SCSI ID = 0 | o o X | SCSI ID = 1 Signal| o o o | | o o X | +-1--3--5-+ +---------+
Ground+---------+ +---------+ MSB | o X o | SCSI ID = 2 | o X X | SCSI ID = 3 Signal| o X o | | o X X | +---------+ +---------+
Ground+---------+ +---------+ MSB | X o o | SCSI ID = 4 | X o X | SCSI ID = 5 Signal| X o o | | X o X | +---------+ +---------+
Ground+---------+ +---------+ MSB | X X o | SCSI ID = 6 | X X X | SCSI ID = 7 Signal| X X o | | X X X | +---------+ +---------+
Each device on the SCSI bus must have a unique SCSI ID. SCSI ID 7 is
typically reserved for the SCSI host adapter.
When selecting the SCSI ID, you can install jumpers on either (not
both) of the following jumper blocks:
- The SCSI ID jumper block
- The user-configuratin jumper block (pins 1-6 only)
J6 Terminator Power Jumper Block
-+3--1+-Circuit board |o o| |o o| +4--2+
+3--1+ From SCSI +3--1+ From Power +3--1+ To SCSI Connector |o X| Conector |xxxx| Connector |X o| Only |o X| |o o| |X o| +4--2+ +4--2+ +4--2+
+3--1+ From Power +3--1+ Terminating |X X| Connector |o o| Resistors |X X| and to SCSI |xxxx| not Installed +4--2+ Bus +4--2+
J9 Active/passive terminaton jumper block
+-5-3-1-+ | o o X | +2.85V to 110ohms | o o X | +-------+
+-5-3-1-+ | X o * | Power and ground to 220/330 ohms | X xxx | +-------+
J8 User-configuration jumper block
-+-------------------1+---Circuit board | o o o o o o o o o *| | o o o o o o o o o o| +20-----------------2+
Pin Function 01 SCSI ID bit 2 (MSB) 02 Ground 03 SCSI ID bit 1 04 Ground 05 SCSI ID bit 0 (LSB) 06 Ground 07 Ext. Spindle sync. 08 Clock ground 09 Remote LED+ 10 Remote LED- 11-20 RESERVED. Do not use.
--5--3--1-+--- --5--3--1-+--- o o * | SCSI ID = 0 X o * | SCSI ID = 1 o o o | X o o | -6--4--2-+ -6--4--2-+
--5--3--1-+--- --5--3--1-+--- o X * | SCSI ID = 2 X X * | SCSI ID = 3 o X o | X X o | -6--4--2-+ -6--4--2-+
--5--3--1-+--- --5--3--1-+--- o o X | SCSI ID = 4 X o X | SCSI ID = 5 o o X | X o X | -6--4--2-+ -6--4--2-+
--5--3--1-+--- --5--3--1-+--- o X X | SCSI ID = 6 X X X | SCSI ID = 7 o X X | X X X | -6--4--2-+ -6--4--2-+
When installing jumpers on the options jumper block and the user-
configuration jumper block, be careful to install jumpers on the
correct pins. Install jumpers only on pins 1 through 4 of the options
jumper block and pins 1 through 6 of the user configuration jumper
Remote LED connection
Remote LED pins are located on two separate jumper blocks: the
options jumpers block and the user-configuration jumper block. Attach
a two-pin remote LED connector to either jumper block, as follows:
- User-configuration jumper block, pins 9 and 10. Use any 2-pin, 2-mm connector and an LED from LiteOn(TM), part number LTL-3231A.
- Options jumper block, pins 7 and 8. Use any 2-pin, 0.1-inch connector and an LED from LiteOn(TM), part number LTL-3231A.
External spindle synchronization option
You can synchronize the spindle motors of an array of drives by
connecting a twisted pair to each drive. The maximum cable length is
6 feet (1.8 meters).
Spindle synchronization pins are located on two separate jumper
blocks: the options jumper block and the user-configuration jumper
block. Use either jumper to synchronize an array of drives, as
- User-configuration jumper block. Use one strand of the twisted pair to connect together pin 7 of the user-configuration jumper block of each drive. Use the other strand to connect together pin 8 of the user-configuration jumper block of each drive.
- Options jumper block. Use one strand of the twisted pair to connect together pin 5 of the options jumper block of each drive. Use the other strand to connect together pin 6 of the options jumper block of each drive.
The spindle-synchronization characteristics can be controlled by the
Mode Select command using the RPL bits in byte 17 of the Rigid Disc
In the default mode, all drives arbitrate during startup see which
drive will be the synchronized master. When the drives are
calibrating their heads, they each check for a reference signal
pulse. The drive that becomes ready first checks for the reference
signal first, and when it does not detect a pulse, it takes over as
the master and begins sending reference pulses. All other drives
synchronize their spindles to the reference signal as they in turn
Parity enable option
When a jumper is installed on pins 1 and 2 of the options jumper
block, the parity bit is used. When a jumper is not installed on pins
1 and 2 of the options jumper block, the parity bit is not used.
When a jumper is installed on pins 3 and 4 of the options jumper
block, the drive waits for a Start/Stop Unit command from the host
before starting or stopping the spindle motor.
Terminator power Source jumper block
To select the termination power source, install jumpers as follows:
- To select the drive power connector as the termination power source for the resistor packs, install a jumper on pins 1 and 3 of the terminator power source jumper block.
- To select the SCSI connector as the termination power source for the resistor packs, install a jumper on pins 1 and 3 of the terminator power source jumper block.
- To provide terminator power to the SCSI connector from the drive terminator packs, install jumpers on pins 1 and 2 and pins 3 and 4 of the terminator power source jumper block.
Active/passive termination jumper block
To select active termination, install a jumper on pins 1 and 2 of the
active/passive termination jumper block. To select passive termina-
tion, install jumpers on pins 5 and 6 and pins 2 and 4 of the active/
passive termination jumper block and change the terminating resistor
SEAGATE ST3390N/3655N PRODUCT MANUAL 36224-001, REV. A, 07/21/93
horizontally vertically +-----------------+ +--+ +--+ | | | +-----+ +-----+ | | | | | | | | | +-+-----------------+-+ | | | | | | +---------------------+ | | | | | | | | | | | | | | | | | | +---------------------+ | +-----+ +-----+ | +-+-----------------+-+ +--+ +--+ | | | | +-----------------+
The drive will operate in all axis (6 directions).
You can mount the drive in any orientation. Follow the guidelines
below appropriate to the set of mounting holes you select to use:
either bottom mounting holes or side mounting holes.
Do not remove factory-installed labels from the drive or cover them
with additional labels. If you do, you could void your warranty.
Factory installed labels contain information required when servicing
Bottom mounting holes
Use 6-32 UNS screws in three of the four available bottom mounting
Do not insert the bottom mounting screws more than 0.20 inches (6
turns) into the drive frame. If you use a screw that is too long, you
could damage the drive.
Side mounting holes
Use 6-32 UNS screws in three of the six available side mounting
Do not insert side mounting screws more than 0.13 inches (4 turns)
into the drive frame. If you use a screw that is too long, you cold
damage the drive.
If there is more than one SCSI device daisy-chained on the bus, you
can connect and disconnect the drive I/O connector and power
connector if the following conditions are met:
- The drive you are disconnecting (or connecting) is not the device supplying terminator power or terminating resistance to the bus.
- Terminator power or resistors must not be added or removed from the bus during hot-plugging.
- The bus must not be used for I/O transactions during hot-plugging. If you are installing a drive on the bus, there must be no I/O transactions until the drive is connected and ready. If you are removing a drive from the bus, there must be no I/O transactions until the drive is completely disconnected.
To avoid damage to the disc and head, th espindle must be completely
stopped and the heads must be parked before you remove the drive from
the system. There are two ways to stop the spindle and park the
- If the drive is not configured to use the remote start/stop feature, disconnect the DC power cable from the drive DC power connector and wait 30 seconds.
- If the drive is configured to use the remote start/stop feature, issue the SCSI stop command and wait 30 seconds.
You can daisy-chain the drive with a maximum of 7 other SCSI devices
(including the host) that have single-ended drivers and receivers
using a common cable. SCSI ID 7, by convention, is usually used for
the host adapter. No drive can have the same SCSI ID as the host
All signals are common between all SCSI devices. The SCSI devices at
both ends of the daisy-chain must be terminated; the intermediate
SCSI devices should not be terminated.
The 50-conductor, nonshielded mating cable connector consists of two
rows of 25 female contacts with adjacent contacts 0.100 inches apart.
The recommended mating cable connector part numbers are shown in the
The following table shows 3M(TM) connector part numbers for interface cable connectors compatible with the drive. These connectors do not have a center key; they are available with or without a strain relief. No strain relief With strain relief No center key No center key Closed end 3M 3M (for cable ends) 3425-7000 3425-7050
Open end 3M 3M
(for daisy-chain) 3425-6000 3425-6050
The following table shows Molex(TM) connector part numbers for
connector that have a center key.
Two strain reliefs, shown in the following table, are available for
the connectors referred to in the previous table.
Molex strain relief, Molex 90170-0050
Molex strain relief, Molex 15-25-1503
The characteristic impedance of the cable should be betwenn 90 ohms
and 140 ohms. However, most available cables have a somewhat lower
characteristic impedance. To minimize discontiniuties and signal
reflections, do not use cables of different impedances on the bus.
Your design may require trade-offs in shielding effextiveness, the
length of the interface cable, the number of loads, and the transfer
rates. If your design uses both shielded and nonshielded cables
within the same SCSI bus, you must allow for the effects of impedance
To minimize noise effects, use a minimum conductor size of 28 AWG.
Use only nonshielded cable connectors. Use a 50-conductor flat cable
or 25-conductor twisted-pair cable.
When using a single-ended SCSI cable, the following requirements
must be met:
- The cable cannot be longer than 6.0 meters.
- A cable stub cannot be longer than 0.1 meter, from the mainline interconnection to any device.
- Stubs must be separated by at least 0.3 meter.
Fast synchronous data transfer
When using fast synchronous data transfer rates, the SCSI interface
cable must meet the following additional requirements:
- The cable cannot be longer than 3.0 meters.
- A characteristic impedance of 90 ohms to 132 ohms is recommended fror nonshielded flat cable or twisted-pair ribbon cable.
- The signal attenuation at 5 MHz must not be greater than 0.095 dB per meter.
- The DC resistance at 20*C must not exceed 0.230 ohms per meter.
- The propagation delay delta of a shielded, twisted-pair cable must not exceed 20 nsec per meter.
The recommended nonshielded flat cable part numbers are shown in the
Part Manufacturer Flat Cable 3M-3365-50 Twisted Pair Spectra Twist-N-Flat 455-248-50
DC power connector
The drive is equipped with s 4-pin power connector.
Internal drive I/O termination consists of three SIP resistor modules
that plug into sockets on the printed circuit boad. You can order
the drive in the active or passive configuration, or without
terminators, depending on your application. When installing or
removing terminators, follow these guidelines:
- All applications involving a single-initiator and a single-target require that both the initiator and the target drive have termiators.
- In daisy-chain application, only the devices at each end of the daisy chain be terminated. All other devices in the chain shoulld not be terminated.
- If your application requires no terminators, remove the terminators from the drive circuit board. Removing the terminator power source selection jumper does not disconnect the terminator resistors from the circuit.
- If you use Fasr SCSI transfer rates, then you must use the active termination options. If the transfer rate is 5.0MB per second or less, you can use either method of termination.
Active termination ------------------ All interface signals are single-ended and must be terminated at the drive with a 110-ohm resistor to +2.85V. The Seagate part number for the 110-ohm terminator is 502155-001.
Passive termination ------------------- All interface signals with the drive are single-ended and must be terminated with 220 ohms to +5V and 330 ohms to ground at each end of the cable. All signals use open-collector drivers or three-state drivers. The Seagate part number for the 220/330-ohm terminator is 75916526-9.
Single-ended SCSI devices providing termination power have the
Terminator voltage (V) 4.0 to 5.25
Source drive capability (mA, min) 800
Single-ended drivers and receivers
The drive uses singled-ended drivers and receivers.
- Transmitter characteristics. The drive uses 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 volts.
- Receiver characteristics. The drive uses an ANSI SCSI single-ended receiver with hysteresis gate or equivalent as a line receiver.
The loss in the cable is defined as the difference between the
voltages of the input and output signals, as shown below:
Logic level Driver output (x) Receiver input (x)
Asserted (1) 0.0V x 0.4V 0.0V x 0.8V Negated (0) 2.5V x 5.25V 2.0V x 5.25V
Jumper Part Numbers
The jumper specifications are described in the table below:
Jumper size Part number Application 2-mm Seagate PN 13211-001 J5 and J8 only Dupont PN 89133-001 Methode PN 8618-202-70, or equivalent
0.1-inch Seagate PN 10562-001 All jumper blocks DuPont PN 86214 except J5 and J8 Molex PN 87092-3013, or equivalent
SEAGATE ST3390N/3655N PRODUCT MANUAL 36224-001, REV. A 21/07/1993
The capacities specified here do not include spare sectors and
cylinders. The media contains one spare sector per track and two
spare cylinders per drive.
Formatted capacity (Mbytes*) ST3390N 344.31 ST3655N 545.29
Total sectors 672,480 1,065,036
* One Mbyte equals one million bytes.
Read error rates are measured with automatic retries and data
correction with ECC enabled and all flaws reallocated. MTBF is
measured at nominal power at sea level and 40*C ambient temperature.
Nonrecoverable read errors 1 per 10(13) bits transferred
Seek errors 1 per 10(7) physical seeks
MTBF 250,000 power-on hours
Service life 5 years
All seek time measurements are taken under nominal conditions of
temperature and voltage with the drive mounted horizontally.
- Track-to-track seek time is the average of all possible single-track seeks in both directions.
- Average/typical seek time is a true statistical random average of at least 5,000 measurements of seeks in both directions between random cylinders, less overhead.
- Full-stroke seek time is one-half the time needed to seek from logical block address zero (LBA 0) to the maximum LBA and back to LBA 0.
- Read/Write. The drive is reading or writing. All electronics are active and the heads are on track. The drive enters this mode from the Idle mode.
- Standby. This mode is not implemented.
The thermal compensation operation compensates for thermal-related
position offset on the selected head. Thermal compensation is
performed during startup and every 2 minutes thereafter. This
periodic compensation coincides with a host command service
operation. The last command execution time increases by 100 msec
typical or 350 msec maximum.
Except during the write procedure, pwoer can be applied or removed
from the drive in any sequence without losing data or damaging the
drive. If you remove the power from the drive during the write
procedure, you may lose the data currently beeing written. A voltage
tolerance of 5% must be maintained under all conditions, including
The drive interface is described in the Seagate SCSI-2 Interface
Manual, publication number 77765466-B. The interface is compatible
with the mandatory subset of the ANSI SCSI-2 Interface.
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,
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.
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
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
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
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
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
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:
- DB(7-0, P); DB(15-8,P1)
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
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
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.
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.
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.
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.
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.
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.
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
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
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
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
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.