Category : HD Utilities
Archive   : SCSI-2.ZIP
Filename : ATA-R23.TXT

Copies of this proposal may be purchased from: BSR X3.***
Global Engineering, 2805 McGaw St, Irvine, CA 92714 X3T9.2/90-143
800-854-7179 714-261-1455





working draft proposed American National
Standard for Information Systems -

ATA (AT Attachment)

Rev 2.3 January 30, 1991




Secretariat

Computer and Business Equipment Manufacturers Association (CBEMA)

Abstract: This standard defines the software interface between device drivers
and the Host Bus Adapters or other means by which SCSI peripherals are
attached to a host processor. The software interface defined provides a common
interface specification for systems manufacturers, system integrators,
controller manufacturers, and suppliers of intelligent peripherals.

This is an internal working document of X3T9.2, a Task Group of Accredited
Standards Committee X3. As such this is not a completed standard. The
contents are actively being modified by the X3T9.2 Task Group. This document
is made available for review and comment only.





POINTS OF CONTACT:

John B. Lohmeyer I. Dal Allan
Chairman X3T9.2 Vice-Chairman X3T9.2
NCR ENDL
3718 N Rock Rd 14426 Black Walnut Court
Wichita KS 67226 Saratoga CA 95070

316-636-8703 408-867-6630



An electronic copy of this document is available from the SCSI Bulletin Board
(316-636-8700).

This document has been prepared according to the style guide of the ISO
(International Organization of Standards).


If this document was printed in a 2-up form directly from the printer, NOTEs
had to be adjusted to fit into a half-page, which may have resulted in an
imperfect representation of the format within the NOTE. This is most likely to
occur if a series of NOTEs are mixed in without any line separation.






This document identifies all changes made since Rev 2.1 of June, 1990.










Foreword (This Foreword is not part of American National Standard X3.***-
199x.)

When the first IBM PC (Personal Computer) (tm) was introduced, there was no
hard disk capability for storage. Successive generations of product resulted
in the inclusion of a hard disk as the primary storage device. When the PC AT
(tm) was developed, a hard disk was the key to system performance, and the
controller interface became a de facto industry interface for the inclusion of
hard disks in PC ATs.

The price of desktop systems has declined rapidly because of the degree of
integration to reduce the number of components and interconnects required to
build a product. A natural outgrowth of this integration was the inclusion of
controller functionality into the hard disk.

In October 1988 a number of peripheral suppliers formed the Common Access
Method Committee to encourage an industry-wide effort to adopt a common
software interface to dispatch input/output requests to SCSI peripherals.
Although this was the primary objective, a secondary goal was to specify what
is known as the AT Attachment interface.

Suggestions for improvement of this standard will be welcome. They should be
sent to the Computer and Business Equipment Manufacturers Association, 311
First Street N.W., Suite 500, Washington, DC 20001.

This standard was processed and approved for submittal to ANSI by the
Accredited Standards Committee on Information Processing Systems, X3.
Committee approval of this standard does not necessarily imply that all
committee members voted for its approval. At the time it approved this
standard, the X3 Committee had the following members:

X3 Committee list goes here:


Subcommittee X3T9 on I/O interfaces, which reviewed this standard, had the
following members:

X3T9 Committee list goes here:




Task Group X3T9.2 on Lower-Level Interfaces, which completed the development
of this standard, had the following members:

X3T9.2 Committee list goes here:



The initial development work on this standard was done by the CAM Committee.

The membership of the CAM Committee consisted of the following organizations:

Adaptec Data Technology NCR
AMD Eastman Kodak Olivetti
Apple Emulex Quantum
AT&T Bell Labs Fujitsu uElectronics Scientific Micro Systems
Caliper Future Domain Seagate
Cambrian Systems Hewlett Packard Sony
Cipher Data IBM Storage Dimensions
Cirrus Logic Imprimis Sun Microsystems
Columbia Data Interactive Systems Syquest Technology
CompuAdd JVC Sytron
Conner Peripherals LMS OSD Trantor
Dell Computer Maxtor Western Digital
Digital Equipment Micropolis
DPT Miniscribe

TABLE OF CONTENTS

1. Scope 1
1.1 Description of Clauses 1

2. References 1
3. General Description 1
3.1 Structure 2

4. Definitions and Conventions 2
4.1 Definitions 2
4.2 Conventions 2

5. Interface Cabling Requirements 3
5.1 Configuration 3
5.2 Addressing Considerations 4
5.3 DC Cable and Connector 4
5.3.1 4-Pin Power 4
5.3.2 3-Pin Power 5
5.3.3 Device Grounding 5

5.4 I/O Connector 5
5.5 I/O Cable 6

6. Physical Interface 6
6.1 Signal Conventions 6
6.2 Signal Summary 7
6.3 Signal Descriptions 9
6.3.1 CS1FX- (Drive chip Select 0) 9
6.3.2 CS3FX- (Drive chip Select 1) 9
6.3.3 DA0-2 (Drive Address Bus) 10
6.3.4 DASP- (Drive Active/Drive 1 Present) 10
6.3.5 DD0-DD15 (Drive Data Bus) 10
6.3.6 DIOR- (Drive I/O Read) 10
6.3.7 DIOW- (Drive I/O Write) 10
6.3.8 DMACK- (DMA Acknowledge) (Optional) 10
6.3.9 DMARQ (DMA Request) (Optional) 11
6.3.10 INTRQ (Drive Interrupt) 11
6.3.11 IOCS16- (Drive 16-bit I/O) 11
6.3.12 IORDY (I/O Channel Ready) (Optional) 12
6.3.13 PDIAG- (Passed Diagnostics) 12
6.3.14 RESET- (Drive Reset) 12
6.3.15 SPSYNC (Spindle Synchronization) (Optional) 12

7. Logical Interface 13
7.1 General 13
7.1.1 Bit Conventions 13
7.1.2 Environment 13

7.2 I/O Register Descriptions 14
7.2.1 Alternate Status Register 14
7.2.2 Command Register 15
7.2.3 Cylinder High Register 15
7.2.4 Cylinder Low Register 15
7.2.5 Data Register 15
7.2.6 Device Control Register 15
7.2.7 Drive Address Register 16
7.2.8 Drive/Head Register 16
7.2.9 Error Register 16
7.2.10 Features Register 17
7.2.11 Sector Count Register 17
7.2.12 Sector Number Register 17
7.2.13 Status Register 18

8. Programming Requirements 19
8.1 Reset Response 19
8.2 Translate Mode 20
8.3 Power Conditions 20
8.4 Error Posting 20

9. Command Descriptions 21
9.1 Check Power Mode 24
9.2 Execute Drive Diagnostic 24
9.3 Format Track 24
9.4 Identify Drive 25
9.4.1 Number of fixed cylinders 27
9.4.2 Number of heads 27
9.4.3 Number of unformatted bytes per track 27
9.4.4 Number of unformatted bytes per sector 27
9.4.5 Number of sectors per track 27
9.4.6 Serial Number 27
9.4.7 Buffer Type 27
9.4.8 Firmware Revision 27
9.4.9 Model Number 27
9.4.10 PIO data transfer cycle timing mode 27
9.4.11 DMA data transfer cycle timing mode 28

9.5 Idle 28
9.6 Idle Immediate 28
9.7 Initialize Drive Parameters 28
9.8 Recalibrate 28
9.9 Read Buffer 29
9.10 Read DMA 29
9.11 Read Long 29
9.12 Read Multiple Command 29
9.13 Read Sector(s) 30
9.14 Read Verify Sector(s) 31
9.15 Seek 31
9.16 Set Features 31
9.17 Set Multiple Mode 31
9.18 Sleep 32
9.19 Standby 32
9.20 Standby Immediate 32
9.21 Write Buffer 32
9.22 Write DMA 33
9.23 Write Multiple Command 33
9.24 Write Same 34
9.25 Write Long 34
9.26 Write Sector(s) 34
9.27 Write Verify 35

10. Protocol Overview 35
10.1 PIO Data In Commands 35
10.1.1 PIO Read Command 36
10.1.2 PIO Read Aborted Command 36

10.2 PIO Data Out Commands 36
10.2.1 PIO Write Command 37
10.2.2 PIO Write Aborted Command 37

10.3 Non-Data Commands 37
10.4 Miscellaneous Commands 37
10.5 DMA Data Transfer Commands (Optional) 38
10.5.1 Normal DMA Transfer 38
10.5.2 Aborted DMA Transfer 38
10.5.3 Aborted DMA Command 39

11. Timing 39
11.1 Deskewing 39
11.2 Symbols 39
11.3 Terms 39
11.4 Data Transfers 40
11.5 Power On and Hard Reset 42

FIGURES

FIGURE 5-1: ATA INTERFACE TO EMBEDDED BUS PERIPHERALS 3
FIGURE 5-2: HOST BUS ADAPTER AND PERIPHERAL DEVICES 4
FIGURE 5-3: ATA INTERFACE TO CONTROLLER AND PERIPHERAL DEVICES 4
FIGURE 5-4: 40-PIN CONNECTOR MOUNTING 6
FIGURE 11-1: PIO DATA TRANSFER TO/FROM DRIVE 40
FIGURE 11-2: IORDY TIMING REQUIRMENTS 41
FIGURE 11-3: DMA DATA TRANSFER 41
FIGURE 11-4 RESET SEQUENCE 42

TABLES

TABLE 5-1: DC INTERFACE 5
TABLE 5-2: DC INTERFACE 5
TABLE 5-3: CABLE PARAMETERS 6
TABLE 6-1: INTERFACE SIGNALS 8
TABLE 6-2: INTERFACE SIGNALS DESCRIPTION 9
TABLE 7-1: I/O PORT FUNCTIONS/SELECTION ADDRESSES 14
TABLE 8-1: POWER CONDITIONS 20
TABLE 8-2: REGISTER CONTENTS 21
TABLE 9-1: COMMAND CODES AND PARAMETERS 23
TABLE 9-2: DIAGNOSTIC CODES 24

Information Processing Systems --

AT Attachment Interface


1. Scope

This standard defines the AT Attachment Interface.

The CAM Committee was formed in October, 1988 and the first working document
of the AT Attachment was introduced in March, 1989.

1.1 Description of Clauses

Clause 1 contains the Scope and Purpose.

Clause 2 contains Referenced and Related International Standards.

Clause 3 contains the General Description.

Clause 4 contains the Glossary.

Clause 5 contains the electrical and mechanical characteristics; covering the
interface cabling requirements of the DC, data cables and connectors.

Clause 6 contains the signal descriptions of the AT Attachment Interface.

Clause 7 contains descriptions of the registers of the AT Attachment
Interface.

Clause 8 describes the programming requirements of the AT Attachment
Interface.

Clause 9 contains descriptions of the commands of the AT Attachment Interface.

Clause 10 contains an overview of the protocol of the AT Attachment Interface.

Clause 11 contains the interface timing diagrams.

Annex A is informative.

Annex B is informative.

2. References

None.

3. General Description

The application environment for the AT Attachment Interface is any computer
which uses an AT Bus or 40-pin ATA interface.

The PC AT Bus (tm) is a widely used and implemented interface for which a
variety of peripherals have been manufactured. As a means of reducing size and
cost, a class of products has emerged which embed the controller functionality
in the drive. These new products utilize the AT Bus fixed disk interface
protocol, and a subset of the AT bus. Because of their compatibility with
existing AT hardware and software this interface quickly became a de facto
industry standard.

The purpose of the ATA standard is to define the de facto implementations.

Software in the Operating System dispatches I/O (Input/Output) requests via
the AT Bus to peripherals which respond to direct commands.

3.1 Structure

This standard relies upon specifications of the mechanical and electrical
characteristics of the AT Bus and a subset of the AT Bus specifically
developed for the direct attachment of peripherals.

Also defined are the methods by which commands are directed to peripherals,
the contents of registers and the method of data transfers.

4. Definitions and Conventions

4.1 Definitions

For the purpose of this standard the following definitions apply:

4.1.1 ATA (AT Attachment): ATA defines a compatible register set and a 40-pin
connector and its associated signals.

4.1.2 Data block: This term describes a data transfer, and is typically a
single sector, except when declared otherwise by use of the Set Multiple
command.

4.1.3 DMA (Direct Memory Access): A means of data transfer between peripheral
and host memory without processor intervention.

4.1.4 Optional: This term describes features which are not required by the
standard. However, if any feature defined by the standard is implemented, it
shall be done in the same way as defined by the standard. Describing a feature
as optional in the text is done to assist the reader. If there is a conflict
between text and tables on a feature described as optional, the table shall be
accepted as being correct.

4.1.5 PIO (Programmed Input/Output): A means of data transfer that requires
the use of the host processor.

4.1.6 Reserved: Where this term is used for bits, bytes, fields and code
values; the bits, bytes, fields and code values are set aside for future
standardization, and shall be zero.

4.1.7 VU (Vendor Unique): This term is used to describe bits, bytes, fields,
code values and features which are not described in this standard, and may be
used in a way that varies between vendors.

4.2 Conventions

Certain terms used herein are the proper names of signals. These are printed
in uppercase to avoid possible confusion with other uses of the same words;
e.g., ATTENTION. Any lowercase uses of these words have the normal American-
English meaning.

A number of conditions, commands, sequence parameters, events, English text,
states or similar terms are printed with the first letter of each word in
uppercase and the rest lowercase; e.g., In, Out, Request Status. Any lowercase
uses of these words have the normal American-English meaning.

The American convention of numbering is used i.e., the thousands and higher
multiples are separated by a comma and a period is used as the decimal point.
This is equivalent to the ISO convention of a space and comma.

American: 0.6 ISO: 0,6
1,000 1 000
1,323,462.9 1 323 462,9

5. Interface Cabling Requirements

5.1 Configuration

This standard provides the capability of operating on the AT Bus in a daisy
chained configuration with a second drive that operates in accordance with
these standards. One drive (selected as Drive 0) has been referred to as the
master in industry terms and the second (selected as Drive 1) has been
referred to as the slave (see Figure 5-3).

The designation as Drive 0 or Drive 1 is made by a jumper plug or switch on
the drive.

Data is transferred in parallel (8 or 16 bits) either to or from host memory
to the drive's buffer under the direction of commands previously transferred
from the host. The drive performs all of the operations necessary to properly
write data to, or read data from, the disk media. Data read from the media is
stored in the drive's buffer pending transfer to the host memory and data is
transferred from the host memory to the drive's buffer to be written to the
media.

+-----------------------------------------------------+
| |
| HOST |
| |
+---------------^-------------------------------------+
| ATA Interface
| _____________________
|/ |
+------v--+ +------v--+
| DRIVE 0 | | DRIVE 1 |
+---------+ +---------+

FIGURE 5-1: ATA INTERFACE TO EMBEDDED BUS PERIPHERALS

+-----------------------------------------------------+
| |
| HOST |
| |
+------+====== AT Bus ======+-------------------------+
| |
| ADAPTER |
| |
+--------^-----------+
| ATA Interface
| _____________________
|/ |
+------v--+ +------v--+
| DRIVE 0 | | DRIVE 1 |
+---------+ +---------+

FIGURE 5-2: HOST BUS ADAPTER AND PERIPHERAL DEVICES

+-----------------------------------------------------+
| |
| HOST |
| |
+---------------^-------------------------------------+
| ATA Interface
+------v-----+
| |
| CONTROLLER |
| |
+-^----^---^-+
| | |__________________ Device Interface
| ___|_________________ | e.g. ESDI, SCSI
|/ | | |
+-v----v--+ +-v----v--+
| DRIVE | | DRIVE |
+---------+ +---------+

FIGURE 5-3: ATA INTERFACE TO CONTROLLER AND PERIPHERAL DEVICES

5.2 Addressing Considerations

In traditional controller operation, only the selected controller receives
commands from the host following selection. In this standard, the register
contents go to both drives (and their embedded controllers). The host
discriminates between the two by using the DRV bit in the Drive/Head Register.

5.3 DC Cable and Connector

The drive receives DC power through a 4-pin or a low-power application 3-pin
connector.

5.3.1 4-Pin Power

The pin assignments are shown in Table 5-1. Recommended part numbers for the
mating connector to 18AWG cable are shown below, but equivalent parts may be
used.

Connector (4 Pin) AMP 1-480424-0 or equivalent.
Contacts (Loose Piece) AMP 60619-4 or equivalent.
Contacts (Strip) AMP 61117-4 or equivalent.

TABLE 5-1: DC INTERFACE
+------------------------+------------+
| POWER LINE DESIGNATION | PIN NUMBER |
+------------------------+------------+
| +12 V | 1-01 |
| +12 V RETURN | 1-02 |
| +5 V RETURN | 1-03 |
| +5 V | 1-04 |
+------------------------+------------+

5.3.2 3-Pin Power

The pin assignments are shown in Table 5-2. Recommended part numbers for the
mating connector to 18AWG cable are shown below, but equivalent parts may be
used.

Connector (3 Pin) Molex 5484 39-27-0032 or equivalent.

TABLE 5-2: DC INTERFACE
+------------------------+------------+
| POWER LINE DESIGNATION | PIN NUMBER |
+------------------------+------------+
| +12 V | 1-01 |
| Ground | 1-02 |
| +5 V | 1-03 |
+------------------------+------------+

5.3.3 Device Grounding

System ground may be connected to a "quick-connect" terminal equivalent to:

Drive Connector Terminal AMP 61664-1 or equivalent.
Cable Connector Terminal AMP 62137-2 or equivalent.

Provision for tying the DC Logic ground and the chassis ground together or for
separating these two ground planes is vendor specific.

5.4 I/O Connector

The I/O connector is a 40-pin connector as shown in Figure 5-4, with pin
assignments as shown in Table 6-1.

The connector should be keyed to prevent the possibility of installing it
upside down. A key is provided by the removal of Pin 20. The corresponding pin
on the cable connector should be plugged.

The pin locations are governed by the cable plug, not the receptacle. The way
in which the receptacle is mounted on the Printed Circuit Board affects the
pin positions, and pin 1 should remain in the same relative position. This
means the pin numbers of the receptacle may not reflect the conductor number
of the plug. The header receptacle is not polarized, and all the signals are
relative to Pin 20, which is keyed.

By using the plug positions as primary, a straight cable can connect drives.
As shown in Figure 5-4, conductor 1 on pin 1 of the plug has to be in the same
relative position no matter what the receptacle numbering looks like. If
receptacle numbering was followed, the cable would have to twist 180 degrees
between a drive with top-mounted receptacles, and a drive with bottom-mounted
receptacles.

+-----------------------+
| 1|
|40 20 2|
==+==== Circuit Board ====+== ==+==== Circuit Board ====+==
| 1|
|40 20 2|
+-----------------------+
FIGURE 5-4: 40-PIN CONNECTOR MOUNTING

Recommended part numbers for the mating connector are shown below, but
equivalent parts may be used.

Connector (40 Pin) 3M 3417-7000 or equivalent.
Strain relief 3M 3448-2040 or equivalent.
Flat Cable (Stranded 28 AWG) 3M 3365-40 or equivalent.
Flat Cable (Stranded 28 AWG) 3M 3517-40 (Shielded) or equivalent.

5.5 I/O Cable

The cable specifications affect system integrity and the maximum length that
can be supported in any application.

TABLE 5-3: CABLE PARAMETERS
+-------------------------------------+------+--------+
| Cable length of 0.46m (18 inches) * | Min | Max |
+-------------------------------------+------+--------+
| Driver IoL Sink Current | 12mA | |
| Driver IoH Source Current | | -400uA |
| Cable Capacitive Loading | | 200pF |
+-------------------------------------+------+--------+
* This distance may be exceeded in circumstances where the
characteristics of both ends of the cable can be controlled.

6. Physical Interface

6.1 Signal Conventions

Signal names are shown in all upper case letters. Signals can be asserted
(active, true) in either a high (more positive voltage) or low (less positive
voltage) state. A dash character (-) at the beginning or end of a signal name
indicates it is asserted at the low level (active low). No dash or a plus
character (+) at the beginning or end of a signal name indicates it is
asserted high (active high). An asserted signal may be driven high or low by
an active circuit, or it may be allowed to be pulled to the correct state by
the bias circuitry.

Control signals that are asserted for one function when high and asserted for
another function when low are named with the asserted high function name
followed by a slash character (/), and the asserted low function name followed
with a dash (-) e.g. BITENA/BITCLR- enables a bit when high and clears a bit
when low. All signals are TTL compatible unless otherwise noted. Negated means
that the signal is driven by an active circuit to the state opposite to the
asserted state (inactive, or false) or may be simply released (in which case
the bias circuitry pulls it inactive, or false), at the option of the

implementor.

6.2 Signal Summary

The physical interface consists of single ended TTL compatible receivers and
drivers communicating through a 40-conductor flat ribbon nonshielded cable
using an asynchronous interface protocol. The pin numbers and signal names are
shown in Table 6-1. Reserved signals shall be left unconnected.

TABLE 6-1: INTERFACE SIGNALS
+----------------------------------+ +-----------+
| HOST I/O | | DRIVE I/O |
| CONNECTOR | | CONNECTOR |
| | | |
| HOST RESET 1 | ----- RESET- -------->| 1 |
| 2 | ----- Ground -------- | 2 |
| HOST DATA BUS BIT 7 3 |<----- DD7 ----------->| 3 |
| HOST DATA BUS BIT 8 4 |<----- DD8 ----------->| 4 |
| HOST DATA BUS BIT 6 5 |<----- DD6 ----------->| 5 |
| HOST DATA BUS BIT 9 6 |<----- DD9 ----------->| 6 |
| HOST DATA BUS BIT 5 7 |<----- DD5 ----------->| 7 |
| HOST DATA BUS BIT 10 8 |<----- DD10 ---------->| 8 |
| HOST DATA BUS BIT 4 9 |<----- DD4 ----------->| 9 |
| HOST DATA BUS BIT 11 10 |<----- DD11 ---------->| 10 |
| HOST DATA BUS BIT 3 11 |<----- DD3 ----------->| 11 |
| HOST DATA BUS BIT 12 12 |<----- DD12 ---------->| 12 |
| HOST DATA BUS BIT 2 13 |<----- DD2 ----------->| 13 |
| HOST DATA BUS BIT 13 14 |<----- DD13 ---------->| 14 |
| HOST DATA BUS BIT 1 15 |<----- DD1 ----------->| 15 |
| HOST DATA BUS BIT 14 16 |<----- DD14 ---------->| 16 |
| HOST DATA BUS BIT 0 17 |<----- DD0 ----------->| 17 |
| HOST DATA BUS BIT 15 18 |<----- DD15 ---------->| 18 |
| 19 | ----- Ground -------- | 19 |
| 20 | ----- (keypin) ------ | 20 |
| DMA REQUEST 21 |<----- DMARQ --------- | 21 |
| 22 | ----- Ground -------- | 22 |
| HOST I/O WRITE 23 | ----- DIOW- --------->| 23 |
| 24 | ----- Ground -------- | 24 |
| HOST I/O READ 25 | ----- DIOR- --------->| 25 |
| 26 | ----- Ground -------- | 26 |
| I/O CHANNEL READY 27 |<----- IORDY --------- | 27 |
| SPINDLE SYNC 28 |*----- SPSYNC --------*| 28 |
| DMA ACKNOWLEDGE 29 | ----- DMACK- -------->| 29 |
| 30 | ----- Ground -------- | 30 |
| HOST INTERRUPT REQUEST 31 |<----- INTRQ --------- | 31 |
| HOST 16 BIT I/O 32 |<----- IOCS16- ------- | 32 |
| HOST ADDRESS BUS BIT 1 33 | ----- DA1 ----------->| 33 |
| PASSED DIAGNOSTICS 34 |*----- PDIAG- --------*| 34 |
| HOST ADDRESS BUS BIT 0 35 | ----- DAO ----------->| 35 |
| HOST ADDRESS BUS BIT 2 36 | ----- DA2 ----------->| 36 |
| HOST CHIP SELECT 0 37 | ----- CS1FX- -------->| 37 |
| HOST CHIP SELECT 1 38 | ----- CS3FX- -------->| 38 |
| DRIVE ACTIVE/DRIVE 1 PRESENT 39 |<----- DASP- ---------*| 39 |
| 40 | ----- Ground -------- | 40 |
+----------------------------------+ +-----------+

* Drive Intercommunication Signals

+---HOST---+ +-Drive 0-+ +-Drive 1-+
| 28 | ----->| 28 28 |<----- SPSYNC ---->| 28 |
| 34 | ----- | 34 34 |<----- PDIAG- ---- | 34 |
| 39 |<----- | 39 39 |<----- DASP- ----- | 39 |
+----------+ +---------+ +---------+

6.3 Signal Descriptions

The interface signals and pins are described in more detail than shown in
Table 6-1. The signals are listed according to function, rather than in
numerical connector pin order. Table 6-2 lists signal name mnemonic, connector
pin number, whether input to (I) or output from (O) the drive, and full signal
name.

TABLE 6-2: INTERFACE SIGNALS DESCRIPTION
+--------+----+-----+
| Signal | Pin| I/O |
+--------+----+-----+-----------------------------------------------------+
| CS1FX- | 37 | I | Drive chip Select 0 |
| CS3FX- | 38 | I | Drive chip Select 1 |
| DA0 | 35 | I | Drive Address Bus - Bit 0 |
| DA1 | 33 | I | - Bit 1 |
| DA2 | 36 | I | - Bit 2 |
| DASP- | 39 | I/O | Drive Active/Drive 1 Present |
| DD0 | 17 | I/O | Drive Data Bus - Bit 0 |
| DD1 | 15 | I/O | - Bit 1 |
| DD2 | 13 | I/O | - Bit 2 |
| DD3 | 11 | I/O | - Bit 3 |
| DD4 | 9 | I/O | - Bit 4 |
| DD5 | 7 | I/O | - Bit 5 |
| DD6 | 5 | I/O | - Bit 6 |
| DD7 | 3 | I/O | - Bit 7 |
| DD8 | 4 | I/O | - Bit 8 |
| DD9 | 6 | I/O | - Bit 9 |
| DD10 | 8 | I/O | - Bit 10 |
| DD11 | 10 | I/O | - Bit 11 |
| DD12 | 12 | I/O | - Bit 12 |
| DD13 | 14 | I/O | - Bit 13 |
| DD14 | 16 | I/O | - Bit 14 |
| DD15 | 18 | I/O | - Bit 15 |
| DIOR- | 25 | I | Drive I/O Read |
| DIOW- | 23 | I | Drive I/O Write |
| DMACK- | 29 | I | DMA Acknowledge |
| DMARQ | 21 | O | DMA Request |
| INTRQ | 31 | O | Drive Interrupt |
| IOCS16-| 32 | O | Drive 16-bit I/O |
| IORDY | 27 | O | I/O Channel Ready |
| PDIAG- | 34 | I/O | Passed Diagnostics |
| RESET- | 1 | I | Drive Reset |
| SPSYNC | 28 | - | Spindle Sync |
| keypin | 20 | - | Pin used for keying the interface connector. |
+--------+----+-----+-----------------------------------------------------+

6.3.1 CS1FX- (Drive chip Select 0)

This is the chip select signal decoded from the host address bus used to
select the Command Block Registers.

6.3.2 CS3FX- (Drive chip Select 1)

This is the chip select signal decoded from the host address bus used to
select the Control Block Registers.

6.3.3 DA0-2 (Drive Address Bus)

This is the 3-bit binary coded address asserted by the host to access a
register or data port in the drive.

6.3.4 DASP- (Drive Active/Drive 1 Present)

This is a time-multiplexed signal which indicates that a drive is active, or
that Drive 1 is present. This signal shall be an open collector output and
each drive shall have a 10K pull-up resistor.

During power on initialization or after RESET- is negated, DASP- shall be
asserted by Drive 1 within 400 msec to indicate that Drive 1 is present.

Drive 0 shall allow up to 450 msec for Drive 1 to assert DASP-. If Drive 1 is
not present, Drive 0 may assert DASP- to drive an activity LED.

DASP- shall be negated following acceptance of the first valid command by
Drive 1 or after 31 seconds, whichever comes first.

Any time after negation of DASP-, either drive may assert DASP- to indicate
that a drive is active.

NOTE: Prior to the development of this standard, products were introduced
which did not time multiplex DASP-. Some used two jumpers to indicate
to Drive 0 whether Drive 1 was present. If such a drive is jumpered to
indicate Drive 1 is present it should work successfully with a Drive 1
which complies with this standard. If installed as Drive 1, such a
drive may not work successfully because it may not assert DASP- for a
long enough period to be recognized. However, it would assert DASP- to
indicate that the drive is active.

6.3.5 DD0-DD15 (Drive Data Bus)

This is an 8- or 16-bit bidirectional data bus between the host and the drive.
The lower 8 bits are used for 8-bit transfers e.g. registers, ECC bytes.

6.3.6 DIOR- (Drive I/O Read)

This is the Read strobe signal. The falling edge of DIOR- enables data from a
register or the data port of the drive onto the host data bus, DD0-DD7 or DD0-
DD15. The rising edge of DIOR- latches data at the host.

6.3.7 DIOW- (Drive I/O Write)

This is the Write strobe signal. The rising edge of DIOW- clocks data from the
host data bus, DD0-DD7 or DD0-DD15, into a register or the data port of the
drive.

6.3.8 DMACK- (DMA Acknowledge) (Optional)

This signal shall be used by the host in response to DMARQ to either
acknowledge that data has been accepted, or that data is available.

6.3.9 DMARQ (DMA Request) (Optional)


This signal, used for DMA data transfers between host and drive, shall be
asserted by the drive when it is ready to transfer data to or from the host.
The direction of data transfer is controlled by DIOR- and DIOW-. This signal
is used in a handshake manner with DMACK- i.e. the drive shall wait until the
host asserts DMACK- before negating DMARQ, and re-asserting DMARQ if there is
more data to transfer.

When a DMA operation is enabled, IOCS16-, CS1FX- and CS3FX- shall not be
asserted and transfers shall be 16-bits wide.

NOTE: ATA products with DMA capability require a pull-down resistor on this
signal to prevent spurious data transfers. This resistor may affect
driver requirements for drives sharing this signal in systems with
unbuffered ATA signals.

6.3.10 INTRQ (Drive Interrupt)

This signal is used to interrupt the host system. INTRQ is asserted only when
the drive has a pending interrupt, the drive is selected, and the host has
cleared nIEN in the Device Control Register. If nIEN=1, or the drive is not
selected, this output is in a high impedance state, regardless of the presence
or absence of a pending interrupt.

INTRQ shall be negated by:

- assertion of RESET- or
- the setting of SRST of the Device Control Register, or
- the host writing the Command Register or
- the host reading the Status Register

NOTE: Some drives may negate INTRQ on a PIO data transfer completion, except
on a single sector read or on the last sector of a multi-sector read.

On PIO transfers, INTRQ is asserted at the beginning of each data block to be
transferred. A data block is typically a single sector, except when declared
otherwise by use of the Set Multiple command. An exception occurs on Format
Track, Write Sector(s), Write Buffer and Write Long commands - INTRQ shall not
be asserted at the beginning of the first data block to be transferred.

On DMA transfers, INTRQ is asserted only once, after the command has
completed.

6.3.11 IOCS16- (Drive 16-bit I/O)

Except for DMA transfers, IOCS16- indicates to the host system that the 16-bit
data port has been addressed and that the drive is prepared to send or receive
a 16-bit data word. This shall be an open collector output.

- When transferring in PIO mode, If IOCS16- is not asserted, transfers shall
be 8-bit using DD0-7.
- When transferring in PIO mode, if IOCS16- is asserted, transfers shall be
16-bit using DD0-15. for 16-bit data transfers.
- When transferring in DMA mode, the host shall use a 16-bit DMA channel and
IOCS16- shall not be asserted.

6.3.12 IORDY (I/O Channel Ready) (Optional)

This signal is negated to extend the host transfer cycle of any host register
access (Read or Write) when the drive is not ready to respond to a data
transfer request. When IORDY is not negated, IORDY shall be in a high
impedance state.

6.3.13 PDIAG- (Passed Diagnostics)

This signal shall be asserted by Drive 1 to indicate to Drive 0 that it has
completed diagnostics. A 10K pull-up resistor shall be used on this signal by
each drive.

Following a power on reset, software reset or RESET-, Drive 1 shall negate
PDIAG- within 1 msec (to indicate to Drive 0 that it is busy). Drive 1 shall
then assert PDIAG- within 30 seconds to indicate that it is no longer busy,
and is able to provide status. After the assertion of PDIAG-, Drive 1 may be
unable to accept commands until it has finished its reset procedure and is
Ready (DRDY=1).

Following the receipt of a valid Execute Drive Diagnostics command, Drive 1
shall negate PDIAG- within 1 msec to indicate to Drive 0 that it is busy and
has not yet passed its drive diagnostics. If Drive 1 is present then Drive 0
shall wait for up to 5 seconds from the receipt of a valid Execute Drive
Diagnostics command for Drive 1 to assert PDIAG-. Drive 1 should clear BSY
before asserting PDIAG-, as PDIAG- is used to indicate that Drive 1 has passed
its diagnostics and is ready to post status.

If DASP- was not asserted by Drive 1 during reset initialization, Drive 0
shall post its own status immediately after it completes diagnostics, and
clear the Drive 1 Status Register to 00h. Drive 0 may be unable to accept
commands until it has finished its reset procedure and is Ready (DRDY=1).

6.3.14 RESET- (Drive Reset)

This signal from the host system shall be asserted for at least 25 usec after
voltage levels have stabilized during power on and negated thereafter unless
some event requires that the drive(s) be reset following power on.

6.3.15 SPSYNC (Spindle Synchronization) (Optional)

This signal may be either input or output to the drive depending on a vendor-
defined switch. If a drive is set to Master the signal is output, and if a
drive is set to slave the signal is input.

There is no requirement that each drive implementation be plug-compatible to
the extent that a multiple vendor drive subsystem be operable. Mix and match
of different manufacturers drives is unlikely because rpm, sync fields, sync
bytes etc need to be virtually identical. However, if drives are designed to
match the following recommendation, controllers can operate drives with a
single implementation.

There can only be one master drive at a time in a configuration. The host or
the drive designated as master can generate SPSYNC at least once per rotation,
but may be at a higher frequency.

SPSYNC received by a drive is used as the synchronization signal to lock the
spindles in step. The time to achieve synchronization varies, and is indicated
by the drive setting DRDY i.e. if the drive does not achieve synchronization
following power on or a reset, it shall not set DRDY.

A master drive or the host generates SPSYNC and transmits it.

A slave drive does not generate SPSYNC and is responsible to synchronize its
index to SPSYNC.

If a drive does not support synchronization, it shall ignore SPSYNC.

In the event that a drive previously synchronized loses synchronization, but
is otherwise operational, it does not clear DRDY.

Prior to the introduction of this standard, this signal was defined as DALE
(Drive Address Latch Enable), and used for an address valid indication from
the host system. If used, the host address and chip selects, DAO through DA2,
CS1FX-, and CS3FX- were valid at the negation of this signal and remained
valid while DALE was negated, therefore, the drive did not need to latch these
signals with DALE.

7. Logical Interface

7.1 General

7.1.1 Bit Conventions

Bit names are shown in all upper case letters except where a lower case n
precedes a bit name. This indicates that when nBIT=0 (bit is zero) the action
is true and when nBIT=1 (bit is one) the action is false. If there is no
preceding n, then when BIT=1 it is true, and when BIT=0 it is false.

A bit can be set to one or cleared to zero and polarity influences whether it
is to be interpreted as true or false:

True BIT=1 nBIT=0
False BIT=0 nBIT=1

7.1.2 Environment

The drives using this interface shall be programmed by the host computer to
perform commands and return status to the host at command completion. When two
drives are daisy chained on the interface, commands are written in parallel to
both drives, and for all except the Execute Diagnostics command, only the
selected drive executes the command. On an Execute Diagnostics command
addressed to Drive 0, both drives shall execute the command, and Drive 1 shall
post its status to Drive 0 via PDIAG-.

Drives are selected by the DRV bit in the Drive/Head Register (see 7.2.8), and
by a jumper or switch on the drive designating it as either a Drive 0 or as
Drive 1. When DRV=0, Drive 0 is selected. When DRV=1, Drive 1 is selected.
When drives are daisy chained, one shall be set as Drive 0 and the other as
Drive 1. When a single drive is attached to the interface it shall be set as
Drive 0.

Prior to the adoption of this standard, some drives may have provided jumpers
to indicate Drive 0 with no Drive 1 present, or Drive 0 with Drive 1 present.

Throughout this document, drive selection always refers to the state of the
DRV bit, and the position of the Drive 0/Drive 1 jumper or switch.

7.2 I/O Register Descriptions

Communication to or from the drive is through an I/O Register that routes the
input or output data to or from registers (selected) by a code on signals from
the host (CS1FX-, CS3FX-, DA2, DA1, DA0, DIOR- and DIOW-).

The Command Block Registers are used for sending commands to the drive or
posting status from the drive.

The Control Block Registers are used for drive control and to post alternate
status.

Table 7-1 lists these registers and the addresses that select them.

Logic conventions are: A = signal asserted
N = signal negated
x = does not matter which it is

TABLE 7-1: I/O PORT FUNCTIONS/SELECTION ADDRESSES
+-------------------------------+-----------------------------------------+
| Addresses | Functions |
|CS1FX-|CS3FX-| DA2 | DA1 | DA0 | READ (DIOR-) | WRITE (DIOW-) |
+------+------+-----+-----+-----+---------------------+-------------------+
| Control Block Registers |
+------+------+-----+-----+-----+---------------------+-------------------+
| N | N | x | x | x | Data Bus High Imped | Not used |
| N | A | 0 | x | X | Data Bus High Imped | Not used |
| N | A | 1 | 0 | x | Data Bus High Imped | Not used |
| N | A | 1 | 1 | 0 | Alternate Status | Device Control |
| N | A | 1 | 1 | 1 | Drive Address | Not used |
+------+------+-----+-----+-----+---------------------+-------------------+
| Command Block Registers |
+------+------+-----+-----+-----+---------------------+-------------------+
| A | N | 0 | 0 | 0 | Data | Data |
| A | N | 0 | 0 | 1 | Error Register | Features |
| A | N | 0 | 1 | 0 | Sector Count | Sector Count |
| A | N | 0 | 1 | 1 | Sector Number | Sector Number |
| A | N | 1 | 0 | 0 | Cylinder Low | Cylinder Low |
| A | N | 1 | 0 | 1 | Cylinder High | Cylinder High |
| A | N | 1 | 1 | 0 | Drive/Head | Drive/Head |
| A | N | 1 | 1 | 1 | Status | Command |
| A | A | x | x | x | Invalid Address | Invalid Address |
+------+------+-----+-----+-----+---------------------+-------------------+

7.2.1 Alternate Status Register

This register contains the same information as the Status Register in the
command block. The only difference being that reading this register does not
imply interrupt acknowledge or clear a pending interrupt.

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| BSY | DRDY | DWF | DSC | DRQ | CORR | IDX | ERR |
+-------+-------+-------+-------+-------+-------+-------+-------+

See 7.2.13 for definitions of the bits in this register.

7.2.2 Command Register

This register contains the command code being sent to the drive. Command
execution begins immediately after this register is written. The executable
commands, the command codes, and the necessary parameters for each command are
listed in Table 9-1.

7.2.3 Cylinder High Register

This register contains the high order bits of the starting cylinder address
for any disk access. At the end of the command, this register is updated to
reflect the current cylinder number. The most significant bits of the cylinder
address shall be loaded into the cylinder high Register.

NOTE: Prior to the introduction of this standard, only the lower 2 bits of
this register were valid, limiting cylinder address to 10 bits i.e.
1,024 cylinders.

7.2.4 Cylinder Low Register

This register contains the low order 8 bits of the starting cylinder address
for any disk access. At the end of the command, this register is updated to
reflect the current cylinder number.

7.2.5 Data Register

This 16-bit register is used to transfer data blocks between the device data
buffer and the host. It is also the register through which sector information
is transferred on a Format Track command. Data transfers may be either PIO or
DMA.

7.2.6 Device Control Register

The bits in this register are as follows:

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| x | x | x | x | 1 | SRST | nIEN | 0 |
+-------+-------+-------+-------+-------+-------+-------+-------+

- SRST is the host software reset bit. The drive is held reset when this bit
is set. If two disk drives are daisy chained on the interface, this bit
resets both simultaneously. Drive 1 is not required to execute the DASP-
handshake procedure.
- nIEN is the enable bit for the drive interrupt to the host. When nIEN=0,
and the drive is selected, INTRQ shall be enabled through a tri-state
buffer. When nIEN=1, or the drive is not selected, the INTRQ signal shall
be in a high impedance state.

7.2.7 Drive Address Register

This register contains the inverted drive select and head select addresses of
the currently selected drive. The bits in this register are as follows:

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| HiZ | nWTG | nHS3 | nHS2 | nHS1 | nHS0 | nDS1 | nDS0 |
+-------+-------+-------+-------+-------+-------+-------+-------+

- HiZ shall always be in a high impedance state.
- nWTG is the Write Gate bit. When writing to the disk drive is in progress,
nWTG=0.
- nHS3 through nHS0 are the one's complement of the binary coded address of
the currently selected head. For example, if nHS3 through nHS0 are 1100b,
respectively, head 3 is selected. nHS3 is the most significant bit.
- nDS1 is the drive select bit for drive 1. When drive 1 is selected and
active, nDS1=0.
- nDS0 is the drive select bit for drive 0. When drive 0 is selected and
active, nDS0=0.

NOTE: Care should be used when interpreting these bits, as they do not
always represent the expected status of drive operations at the
instant the status was put into this register. This is because of the
use of cacheing, translate mode and the Drive 0/Drive 1 concept with
each drive having its own embedded controller.

7.2.8 Drive/Head Register

This register contains the drive and head numbers. The contents of this
register define the number of heads minus 1, when executing an Initialize
Drive Parameters command.

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| 1 | 0 | 1 | DRV | HS3 | HS2 | HS1 | HS0 |
+-------+-------+-------+-------+-------+-------+-------+-------+

- DRV is the binary encoded drive select number. When DRV=0, Drive 0 is
selected. When DRV=1, Drive 1 is selected.
- HS3 through HS0 contain the binary coded address of the head to be selected
e.g. if HS3 through HS0 are 0011b, respectively, head 3 will be selected.
HS3 is the most significant bit. At command completion, this register is
updated to reflect the currently selected head.

7.2.9 Error Register

This register contains status from the last command executed by the drive or a
Diagnostic Code.

At the completion of any command except Execute Drive Diagnostic, the contents
of this register are valid when ERR=1 in the Status Register.

Following a power on, a reset, or completion of an Execute Drive Diagnostic
command, this register contains a Diagnostic Code (see Table 9-2).

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| BBK | UNC | 0 | IDNF | 0 | ABRT | TK0NF | AMNF |
+-------+-------+-------+-------+-------+-------+-------+-------+

- BBK (Bad Block Detected) indicates a bad block mark was detected in the
requested sector's ID field.
- UNC (Uncorrectable Data Error) indicates an uncorrectable data error has
been encountered.
- IDNF (ID Not Found) indicates the requested sector's ID field could not be
found.
- ABRT (Aborted Command) indicates the requested command has been aborted due
to a drive status error (Not Ready, Write Fault, etc.) or because the
command code is invalid.
- TK0NF (Track 0 Not Found) indicates track 0 has not been found during a
Recalibrate command.
- AMNF (Address Mark Not Found) indicates the data address mark has not been
found after finding the correct ID field.
- Unused bits are cleared to zero.

7.2.10 Features Register

This register is command specific and may be used to enable and disable
features of the interface e.g. by the Set Features Command to enable and
disable cacheing.

This register may be ignored by some drives.

Some hosts, based on definitions prior to the completion of this standard, set
values in this register to designate a recommended Write Precompensation
Cylinder value.

7.2.11 Sector Count Register

This register contains the number of sectors of data requested to be
transferred on a read or write operation between the host and the drive. If
the value in this register is zero, a count of 256 sectors is specified.

If this register is zero at command completion, the command was successful. If
not successfully completed, the register contains the number of sectors which
need to be transferred in order to complete the request.

The contents of this register may be defined otherwise on some commands e.g.
Initialize Drive Parameters, Format Track or Write Same commands.

7.2.12 Sector Number Register

This register contains the starting sector number for any disk data access for
the subsequent command. The sector number may be from 1 to the maximum number
of sectors per track.

See the command descriptions for contents of the register at command
completion (whether successful or unsuccessful).

7.2.13 Status Register

This register contains the drive status. The contents of this register are
updated at the completion of each command. When BSY is cleared, the other bits
in this register shall be valid within 400 nsec. If BSY=1, no other bits in
this register are valid. If the host reads this register when an interrupt is
pending, it is considered to be the interrupt acknowledge. Any pending
interrupt is cleared whenever this register is read.

NOTE: If Drive 1 is not detected as being present, Drive 0 clears the Drive
1 Status Register to 00h (indicating that the drive is Not Ready).

7 6 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| BSY | DRDY | DWF | DSC | DRQ | CORR | IDX | ERR |
+-------+-------+-------+-------+-------+-------+-------+-------+

NOTE: Prior to the definition of this standard, DRDY and DSC were unlatched
real time signals.

- BSY (Busy) is set whenever the drive has access to the Command Block
Registers. The host should not access the Command Block Register when
BSY=1. When BSY=1, a read of any Command Block Register shall return the
contents of the Status Register. This bit is set by the drive (which may be
able to respond at times when the media cannot be accessed) under the
following circumstances:
a) within 400 nsec after the negation of RESET- or after SRST has been set
in the Device Control Register. Following acceptance of a reset it is
recommended that BSY be set for no longer than 30 seconds by Drive 1 and
no longer than 31 seconds by Drive 0.
b) within 400 nsec of a host write of the Command Register with a Read,
Read Long, Read Buffer, Seek, Recalibrate, Initialize Drive Parameters,
Read Verify, Identify Drive, or Execute Drive Diagnostic command.
c) within 5 usecs following transfer of 512 bytes of data during execution
of a Write, Format Track, or Write Buffer command, or 512 bytes of data
and the appropriate number of ECC bytes during the execution of a Write
Long command.
- DRDY (Drive Ready) indicates that the drive is capable of responding to a
command. When there is an error, this bit is not changed until the Status
Register is read by the host, at which time the bit again indicates the
current readiness of the drive. This bit shall be cleared at power on and
remain cleared until the drive is ready to accept a command.
- DWF (Drive Write Fault) indicates the current write fault status. When an
error occurs, this bit shall not be changed until the Status Register is
read by the host, at which time the bit again indicates the current write
fault status.
- DSC (Drive Seek Complete) indicates that the drive heads are settled over a
track. When an error occurs, this bit shall not be changed until the Status
Register is read by the host, at which time the bit again indicates the
current Seek Complete status.
- DRQ (Data Request) indicates that the drive is ready to transfer a word or
byte of data between the host and the drive.
- CORR (Corrected Data) indicates that a correctable data error was
encountered and the data has been corrected. This condition does not
terminate a data transfer.
- IDX (Index) is set once per disk revolution.
- ERR (Error) indicates that an error occurred during execution of the
previous command. The bits in the Error Register have additional
information regarding the cause of the error.

8. Programming Requirements

8.1 Reset Response

A reset is accepted within 400 nsec after the negation of RESET- or within 400
nsec after SRST has been set in the Device Control Register.

When the drive is reset by RESET-, Drive 1 shall indicate it is present by
asserting DASP- within 400 msec, and DASP- shall remain asserted for 30
seconds or until Drive 1 accepts the first command. See also 6.3.4 and 6.3.13.

When the drive is reset by SRST, the drive shall set BSY=1.

See also 7.2.6.

When a reset is accepted, and with BSY set:

a) Both drives perform any necessary hardware initialization
b) Both drives clear any previously programmed drive parameters
c) Both drives may revert to the default condition
d) Both drives load the Command Block Registers with their default values
e) If a hardware reset, Drive 0 waits for DASP- to be asserted by Drive 1
f) If operational, Drive 1 asserts DASP-
g) Drive 0 waits for PDIAG- to be asserted if Drive 1 asserts DASP-
h) If operational, Drive 1 clears BSY
i) If operational, Drive 1 asserts PDIAG-
j) Drive 0 clears BSY

No interrupt is generated when initialization is complete.

The default values for the Command Block Registers if no self-tests are
performed or if no errors occurred are:

Error = 01h Cylinder Low = 00h
Sector Count = 01h Cylinder High = 00h
Sector Number = 01h Drive/Head = 00h

The Error Register shall contain a Diagnostic Code (see Table 9.2) if a self-
test is performed.

Following any reset, the host should issue an Initialize Drive Parameters
command to ensure the drive is initialized as desired.

There are three types of reset in ATA. The following is a suggested method of
classifying reset actions:

- Power On Reset: the drive executes a series of electrical circuitry
diagnostics, spins up the HDA, tests speed and other mechanical
parametrics, and sets default values.
- Hardware Reset: the drive executes a series of electrical circuitry
diagnostics, and resets to default values.
- Software Reset: the drive resets the interface circuitry to default values.

8.2 Translate Mode

The cylinder, head and sector geometry of the drive as presented to the host
may differ from the actual physical geometry. Translate mode is an optional
and device specific means of mapping between the two.

8.3 Power Conditions

Optional power commands permit the host to modify the behavior of the drive in
a manner which reduces the power required to operate.

TABLE 8-1: POWER CONDITIONS
+----------+----+----+----+------------------+-----+
| Mode |SRST| BSY|DRDY| Interface Active |Media|
+----------+----+----+----+------------------+-----+
| Sleep | 1 | x | x | No | 0 |
| | | | | | |
| Standby | x | 0 | 1 | Yes | 0 |
| | | | | | |
| Idle | x | 0 | 1 | Yes | 1 |
| | | | | | |
| Active | x | x | x | Yes | 1 |
+----------+----+----+----+------------------+-----+
| 1 = Active 0 = Inactive |
+--------------------------------------------------+

The lowest power consumption occurs in Sleep mode. When in Sleep mode, the
drive needs a Software Reset to be activated (see 9.18). The time to respond
could be as long as 30 seconds or more.

In Standby mode the drive interface is capable of accepting commands, but as
the media is not immediately accessible, it could take the drive as long as 30
seconds or more to respond.

In Idle mode the drive is capable of responding immediately to media access
requests. A drive in Idle mode may take longer to complete the execution of a
command because it may have to activate some circuitry.

In Active mode the drive is capable of responding immediately to media access
requests, and commands complete execution in the shortest possible time.

Ready is not a power condition. A drive may post ready at the interface even
though the media may not be accessible.

See specific power-related commands.

8.4 Error Posting

The errors that are valid for each command are defined in Table 8-1. It is not
a requirement that all valid conditions be implemented. See 7.2.9 and 7.2.13
for the definition of the Error Register and Status Register bits.

TABLE 8-2: REGISTER CONTENTS
+----------------------------+---------------------+
| Error Register | Status Register |
|BBK|UNC|IDNF|ABRT|TK0NF|AMNF|DRDY|DWF|DSC|CORR|ERR|

+------------------------+---+---+----+----+-----+----+----+---+---+----+---+
| Check Power Mode | | | | V | | | V | V | V | | V |
| Execute Drive Diags | See 9.2 | | | | | V |
| Format Track | | | V | V | | | V | V | V | | V |
| Identify Drive | | | | V | | | V | V | V | | V |
| Idle | | | | V | | | V | V | V | | V |
| Idle Immediate | | | | V | | | V | V | V | | V |
| Initialize Drive Parms | | | | | | | V | V | V | | |
| Recalibrate | | | | V | V | | V | V | V | | V |
| Read Buffer | | | | V | | | V | V | V | | V |
| Read DMA | V | V | V | V | | V | V | V | V | V | V |
| Read Long | V | V | V | V | | V | V | V | V | V | V |
| Read Multiple | V | V | V | V | | V | V | V | V | V | V |
| Read Sector(s) | V | V | V | V | | V | V | V | V | V | V |
| Read Verify Sector(s) | V | V | V | V | | V | V | V | V | V | V |
| Seek | | | V | V | | | V | V | V | | V |
| Set Features | | | | V | | | V | V | V | | V |
| Set Multiple Mode | | | | V | | | V | V | V | | V |
| Sleep | | | | V | | | V | V | V | | V |
| Standby | | | | V | | | V | V | V | | V |
| Standby Immediate | | | | V | | | V | V | V | | V |
| Write Buffer | | | | V | | | V | V | V | | V |
| Write DMA | V | | V | V | | | V | V | V | | V |
| Write Long | V | | V | V | | | V | V | V | | V |
| Write Multiple | V | | V | V | | | V | V | V | | V |
| Write Same | V | | V | V | | | V | V | V | | V |
| Write Sector(s) | V | | V | V | | | V | V | V | | V |
| Write Verify | V | V | V | V | | V | V | V | V | V | V |
+------------------------+---+---+----+----+-----+----+----+---+---+----+---+
| Invalid Command Code | | | | V | | | V | V | V | | V |
+------------------------+---+---+----+----+-----+----+----+---+---+----+---+
| V = valid on this command |
+---------------------------------------------------------------------------+

9. Command Descriptions

Commands are issued to the drive by loading the pertinent registers in the
command block with the needed parameters, and then writing the command code to
the Command Register.

The manner in which a command is accepted varies. There are three classes (see
Table 9-1) of command acceptance, all predicated on the fact that to receive a
command, BSY=0:

- Upon receipt of a Class 1 command, the drive sets BSY within 400 nsec.
- Upon receipt of a Class 2 command, the drive sets BSY within 400 nsec, sets
up the sector buffer for a write operation, sets DRQ within 700 usec, and
clears BSY within 400 nsec of setting DRQ.
- Upon receipt of a Class 3 command, the drive sets BSY within 400 nsec, sets
up the sector buffer for a write operation, sets DRQ within 20 msec, and
clears BSY within 400 nsec of setting DRQ.

NOTE: DRQ may be set so quickly on Class 2 and Class 3 that the BSY
transition is too short for BSY=1 to be recognized.

The drive shall implement all mandatory commands as identified by an M, and
may implement the optional commands identified by an O, in Table 9-1. V
indicates a Vendor Specific command code.

If a new command is issued to a drive which has an uncompleted command
(subsequently referred to as Old_Command) in progress, the drive shall
immediately respond to the new command (Subsequently referred to as
New_Command), even if execution of the Old_Command could have been completed.

There shall be no indication given to the system as to the status of the
Old_Command which was being executed at the time the New_Command was issued.

TABLE 9-1: COMMAND CODES AND PARAMETERS
+-------+-------------------+
+-----+ |Command| Parameters Used |
|Class| | Code |FR SC SN CY DH |
+-----+----------------------------------+---+-------+---+---+---+---+---+
| 1 | Check Power Mode | O |98h E5h| | y | | | D |
| 1 | Execute Drive Diagnostic | M | 90h | | | | | D*|
| 2 | Format Track | M | 50h | * | y | | y | y |
| 1 | Identify Drive | O | ECh | | | | | D |
| 1 | Idle | O |97h E3h| | y | | | D |
| 1 | Idle Immediate | O |95h E1h| | | | | D |
| 1 | Initialize Drive Parameters | M | 91h | | y | | | y |
| 1 | Recalibrate | M | 1xh | | | | | D |
| 1 | Read Buffer | O | E4h | | | | | D |
| 1 | Read DMA (w/retry) | O | C8h | | y | y | y | y |
| 1 | Read DMA (w/o retry) | O | C9h | | y | y | y | y |
| 1 | Read Multiple | O | C4h | | y | y | y | y |
| 1 | Read Sector(s) (w/retry) | M | 20 | | y | y | y | y |
| 1 | Read Sector(s) (w/o retry) | M | 21 | | y | y | y | y |
| 1 | Read Long (w/retry) See 9.13 | M | 22 | | y | y | y | y |
| 1 | Read Long (w/o retry) See 9.13 | M | 23 | | y | y | y | y |
| 1 | Read Verify Sector(s) (w/retry) | M | 40 | | y | y | y | y |
| 1 | Read Verify Sector(s) (w/o retry)| M | 41 | | y | y | y | y |
| 1 | Seek | M | 7xh | | | y | y | y |
| 1 | Set Features | O | EFh | y | | | | D |
| 1 | Set Multiple Mode | O | C6h | | y | | | D |
| 1 | Set Sleep Mode | O |99h E6h| | | | | D |
| 1 | Standby | O |96h E2h| | y | | | D |
| 1 | Standby Immediate | O |94h E0h| | | | | D |
| 2 | Write Buffer | O | E8h | | | | | D |
| 3 | Write DMA (w/retry) | O | CAh | | y | y | y | y |
| 3 | Write DMA (w/o retry) | O | CBh | | y | y | y | y |
| 3 | Write Multiple | O | C5h | * | y | y | y | y |
| 3 | Write Same | O | E9h | y | y | y | y | y |
| 2 | Write Sector(s) (w/retry) | M | 30 | * | y | y | y | y |
| 2 | Write Sector(s) (w/o retry) | M | 31 | * | y | y | y | y |
| 2 | Write Long (w/retry) | M | 32 | * | y | y | y | y |
| 2 | Write Long (w/o retry) | M | 33 | * | y | y | y | y |
| 3 | Write Verify | O | 3Ch | * | y | y | y | y |
| | Vendor Unique | V | 9Ah | | | | | |
| | Vendor Unique | V | C0-C3h| | | | | |
| | Vendor Unique | V | 8xh | | | | | |
| | Vendor Unique | V |F0h-FFh| | | | | |
| | Reserved: All remaining codes | | | | | | | |
+-----+----------------------------------+---+-------+---+---+---+---+---+
| | CY = Cylinder Registers SC = Sector Count Register |
| | DH = Drive/Head Register SN = Sector Number Register |
| | FR = Features Register (see command descriptions for use) |
| | y - the register contains a valid parameter for this command. |
| | For the Drive/Head Register, y means both the drive and |
| | head parameters are used. |
| | D - only the drive parameter is valid and not the head parameter.|
| | D* - Addressed to Drive 0 but both drives execute it. |
| | * - Maintained for compatibility (see 7.2.9) |
+-----+------------------------------------------------------------------+

9.1 Check Power Mode

This command checks the power mode.

If the drive is in, going to, or recovering from the Standby Mode the drive
shall set BSY, set the Sector Count Register to 00h, clear BSY, and generate
an interrupt.

If the drive is in the Idle Mode, the drive shall set BSY, set the Sector
Count Register to FFh, clear BSY, and generate an interrupt.

9.2 Execute Drive Diagnostic

This command shall perform the internal diagnostic tests implemented by the
drive. See also 6.3.4 and 6.3.13. The DRV bit is ignored. Both drives, if
present, shall execute this command.

If Drive 1 is present:

- Drive 0 waits up to 5 seconds for Drive 1 to assert PDIAG-.
- If Drive 1 has not asserted PDIAG-, indicating a failure, Drive 0 shall
append 80h to its own diagnostic status.
- Both drives shall execute diagnostics.
- If Drive 1 diagnostic failure is detected when Drive 0 status is read,
Drive 1 status is obtained by setting the DRV bit, and reading status.

If there is no Drive 1 present:

- Drive 0 posts only its own diagnostic results.
- Drive 0 clears BSY, and generates an interrupt.

The Diagnostic Code written to the Error Register is a unique 8-bit code as
shown in Table 9-2, and not as the single bit flags defined in 7.2.9.

If Drive 1 fails diagnostics, Drive 0 "ORs" 80h with its own status and loads
that code into the Error Register. If Drive 1 passes diagnostics or there is
no Drive 1 connected, Drive 0 "ORs" 00h with its own status and loads that
code into the Error Register.

TABLE 9-2: DIAGNOSTIC CODES
+-------+
| Code |
+-------+----------------------------------+
| 01h | No error detected |
| 02h | Formatter device error |
| 03h | Sector buffer error |
| 04h | ECC circuitry error |
| 05h | Controlling microprocessor error |
| 8xh | Drive 1 failed |
+-------+----------------------------------+

9.3 Format Track

The implementation of the Format Track command is vendor specific. The actions
may be a physical reformatting of a track, initializing the data field
contents to some value, or doing nothing.

The Sector Count Register contains the number of sectors per track.

The track address is specified in the Cylinder High and Cylinder Low
Registers, and the number of sectors is specified in the Sector Count
Register. When the command is accepted, the drive sets the DRQ bit and waits
for the host to fill the sector buffer. When the sector buffer is full, the
drive clears DRQ, sets BSY and begins command execution.

The contents of the sector buffer shall not be written to the media, and may
be either ignored or interpreted as follows:

DD15 ---- DD0 DD15 ---- DD0
+------+------+ +------+------+--------------------------+
| First|Desc- | | Last |Desc- | Remainder of buffer |
|Sector|riptor| : : : : : : |Sector|riptor| filled with zeros |
+------+------+ +------+------+--------------------------+

One 16-bit word represents each sector, the words being contiguous from the
start of a sector. Any words remaining in the buffer after the representation
of the last sector are filled with zeros. DD15-8 contain the sector number. If
an interleave is specified, the words appear in the same sequence as they
appear on the track. DD7-0 contain a descriptor value defined as follows:

00h - Format sector as good
20h - Unassign the alternate location for this sector
40h - Assign this sector to an alternate location
80h - Format sector as bad

NOTE: Some users of the ATA drive expect the operating system partition
table to be erased on a Format command. It is recommended that a drive
which does not perform a physical format of the track, write a data
pattern of all zeros to the sectors which have been specified by the
Format Track command.

NOTE: It is recommended that implementors resassign data blocks which show
repeated errors.

9.4 Identify Drive

The Identify Drive command enables the host to receive parameter information
from the drive. When the command is issued, the drive sets BSY, stores the
required parameter information in the sector buffer, sets DRQ, and generates
an interrupt. The host then reads the information out of the sector buffer.
The parameter words in the buffer have the arrangement and meanings defined in
Table 9-3. All reserved bits or words shall be zero.

+-------+ TABLE 9-3: IDENTIFY DRIVE INFORMATION
| Word |
+-------+------------------------------------------------------------------+
| 0 | General configuration bit-significant information: |
| | 15 0 reserved for non-magnetic drives |
| | 14 1=format speed tolerance gap required |
| | 13 1=track offset option available |
| | 12 1=data strobe offset option available |
| | 11 1=rotational speed tolerance is > 0.5% |
| | 10 1=disk transfer rate > 10 Mbs |
| | 9 1=disk transfer rate > 5Mbs but <= 10Mbs |
| | 8 1=disk transfer rate <= 5Mbs |
| | 7 0 reserved for removable cartridge drive |
| | 6 1=fixed drive |
| | 5 1=spindle motor control option implemented |
| | 4 1=head switch time > 15 usec |
| | 3 1=not MFM encoded |
| | 2 1=soft sectored |
| | 1 1=hard sectored |
| | 0 0=reserved |
| 1 | Number of fixed cylinders |
| 2 | reserved |
| 3 | Number of heads |
| 4 | Number of unformatted bytes per track |
| 5 | Number of unformatted bytes per sector |
| 6 | Number of sectors per track |
| 7-9 | Vendor Unique |
| 10-19 | Serial number (20 ASCII characters, 0000h=not specified) |
| 20 | Buffer type |
| 21 | Buffer size in 512 byte increments (0000h=not specified) |
| 22 | # of ECC bytes passed on Read/Write Long cmds (0000h=not spec'd) |
| 23-26 | Firmware revision (8 ASCII characters, 0000h=not specified) |
| 27-46 | Model number (40 ASCII characters, 0000h=not specified) |
| 47 | 15-8 Vendor Unique |
| | 7-0 00h = Read/Write Multiple commands not implemented |
| | xxh = Maximum number of sectors that can be transferred |
| | per interrupt on Read and Write Multiple commands |
| 48 | 0000h = cannot perform doubleword I/O |
| | 0001h = can perform doubleword I/O |
| 49 | Capabilities |
| | 15-9 0=reserved |
| | 8 1=DMA Supported |
| | 7-0 Vendor Unique |
| 50 | reserved |
| 51 | 15-8 PIO data transfer cycle timing mode |
| | 7-0 Vendor Unique |
| 52 | 15-8 DMA data transfer cycle timing mode |
| | 7-0 Vendor Unique |
| 53-127| reserved |
|128-159| Vendor Unique |
|160-255| reserved |
+-------+------------------------------------------------------------------+

The fields described in 9.4.1 through 9.4.5 are not affected by the Initialize
Drive Parameters command.

9.4.1 Number of fixed cylinders

The number of translated cylinders in the default translation mode.

9.4.2 Number of heads

The number of translated heads in the default translation mode.

9.4.3 Number of unformatted bytes per track

The number of unformatted bytes per translated track in the default
translation mode.

9.4.4 Number of unformatted bytes per sector

The number of unformatted bytes per sector in the default translation mode.

9.4.5 Number of sectors per track

The number of sectors per track in the default translation mode.

9.4.6 Serial Number

The contents of this field are right justified and padded with spaces (20h).

9.4.7 Buffer Type

The contents of the field are determined by the manufacturer.

0000h = not specified.
0001h = a single ported single sector buffer which is not capable of
simultaneous data transfers to or from the host and the disk.
0002h = a dual ported multi-sector buffer capable of simultaneous data
transfers to or from the host and the disk.
0003h = a dual ported multi-sector buffer capable of simultaneous transfers
with a read cacheing capability.
0004-FFFFh = reserved

These codes are typically not used by the operating system, however, they are
useful for diagnostic programs which perform initialization routines e.g. a
different interleave may be desirable for 0001h vs 0002h or 0003h.

9.4.8 Firmware Revision

The contents of this field are left justified and padded with spaces (20h).

9.4.9 Model Number

The contents of this field are left justified and padded with spaces (20h).

9.4.10 PIO data transfer cycle timing mode

The PIO transfer timing for each ATA device falls into categories which have
unique parametric timing specifications. To determine the proper device timing
category, compare the Cycle Time specified in Figure 11-1 with the contents of
this field. The value returned in Bits 15-8 should fall into one of the
categories specified in Figure 11-1, and if it does not, then Mode 0 shall be
used to serve as the default timing.

9.4.11 DMA data transfer cycle timing mode

The DMA transfer timing for each ATA device falls into categories which have
unique parametric timing specifications. To determine the proper device timing
category, compare the Cycle Time specified in Figure 11-3 with the contents of
this field. The value returned in Bits 15-8 should fall into one of the
categories specified in Figure 11-3, and if it does not, then Mode 0 shall be
used to serve as the default timing.

9.5 Idle

This command causes the drive to set BSY, enter the Idle Mode, clear BSY, and
generate an interrupt. The interrupt is generated even though the drive may
not have fully transitioned to Idle Mode.

If the drive is already spinning, the spinup sequence is not executed.

If the Sector Count Register is non-zero then the automatic power down
sequence shall be enabled and the timer begins counting down immediately. If
the Sector Count Register is zero then the automatic power down sequence shall
be disabled.

9.6 Idle Immediate

This command causes the drive to set BSY, enter the Idle Mode, clear BSY, and
generate an interrupt. The interrupt is generated even though the drive may
not have fully transitioned to Idle Mode.

9.7 Initialize Drive Parameters

This command enables the host to set the number of sectors per track and the
number of heads minus 1, per cylinder. Upon receipt of the command, the drive
sets BSY, saves the parameters, clears BSY, and generates an interrupt.

The only two register values used by this command are the Sector Count
Register which specifies the number of sectors per track, and the Drive/Head
Register which specifies the number of heads minus 1. The DRV bit designates
these values to Drive 0 or Drive 1, as appropriate.

The sector count and head values are not checked for validity by this command.
If they are invalid, no error will be posted until an illegal access is made
by some other command.

9.8 Recalibrate

This command moves the read/write heads from anywhere on the disk to cylinder
0. Upon receipt of the command, the drive sets BSY and issues a seek to
cylinder zero. The drive then waits for the seek to complete before updating
status, clearing BSY and generating an interrupt.

If the drive cannot reach cylinder 0, a Track Not Found error is posted.

9.9 Read Buffer

The Read Buffer command enables the host to read the current contents of the
drive's sector buffer. When this command is issued, the drive sets BSY, sets
up the sector buffer for a read operation, sets DRQ, clears BSY, and generates
an interrupt. The host then reads up to 512 bytes of data from the buffer.

The Read Buffer and Write Buffer commands shall be synchronized such that
sequential Write Buffer and Read Buffer commands access the same 512 bytes
within the buffer.

9.10 Read DMA

This command executes in a similar manner to the Read Sectors command except
for the following:

- the host initializes a slave-DMA channel prior to issuing the command
- data transfers are qualified by DMARQ and are performed by the slave-DMA
channel
- the drive issues only one interrupt per command to indicate that data
transfer has terminated and status is available.

Any unrecoverable error encountered during execution of a Read DMA command
results in the termination of data transfer at the sector where the error was
detected. The sector in error is not transferred. The drive generates an
interrupt to indicate that data transfer has terminated and status is
available. The error posting is the same as that of the Read Sectors command.

9.11 Read Long

The Read Long command performs similarly to the Read Sectors command except
that it returns the data and the ECC bytes contained in the data field of the
desired sector. During a Read Long command, the drive does not check the ECC
bytes to determine if there has been a data error. Only single sector read
long operations are supported.

The transfer of the ECC bytes shall be 8-bits wide.

9.12 Read Multiple Command

The Read Multiple command performs similarly to the Read Sectors command.
Interrupts are not generated on every sector, but on the transfer of a block
which contains the number of sectors defined by a Set Multiple command.

Command execution is identical to the Read Sectors operation except that the
number of sectors defined by a Set Multiple command are transferred without
intervening interrupts. DRQ qualification of the transfer is required only at
the start of the data block, not on each sector.

The block count of sectors to be transferred without intervening interrupts is
programmed by the Set Multiple Mode command, which shall be executed prior to
the Read Multiple command.

When the Read Multiple command is issued, the Sector Count Register contains
the number of sectors (not the number of blocks or the block count) requested.


If the number of requested sectors is not evenly divisible by the block count,
as many full blocks as possible are transferred, followed by a final, partial
block transfer. The partial block transfer shall be for n sectors, where

n = Remainder (Sector Count / Block Count)

If the Read Multiple command is attempted before the Set Multiple Mode command
has been executed or when Read Multiple commands are disabled, the Read
Multiple operation shall be rejected with an Aborted Command error.

Disk errors encountered during Read Multiple commands are posted at the
beginning of the block or partial block transfer, but DRQ is still set and the
data transfer shall take place as it normally would, including transfer of
corrupted data, if any.

The contents of the Command Block Registers following the transfer of a data
block which had a sector in error are undefined. The host should retry the
transfer as individual requests to obtain valid error information.

Subsequent blocks or partial blocks are transferred only if the error was a
correctable data error. All other errors cause the command to stop after
transfer of the block which contained the error. Interrupts are generated when
DRQ is set at the beginning of each block or partial block.

9.13 Read Sector(s)

This command reads from 1 to 256 sectors as specified in the Sector Count
register. A sector count of 0 requests 256 sectors. The transfer begins at the
sector specified in the Sector Number Register. See 10.1 for the DRQ, IRQ and
BSY protocol on data transfers.

If the drive is not already on the desired track, an implied seek is
performed. Once at the desired track, the drive searches for the appropriate
ID field.

If retries are disabled and two index pulses have occurred without error free
reading of the requested ID, an ID Not Found error is posted.

If retries are enabled, up to a vendor specific number of attempts may be made
to read the requested ID before posting an error.

If the ID is read correctly, the data address mark shall be recognized within
a specified number of bytes, or the Address Mark Not Found error is posted.

DRQ is always set prior to data transfer regardless of the presence or absence
of an error condition.

At command completion, the Command Block Registers contain the cylinder, head,
and sector number of the last sector read.

If an error occurs, the read terminates at the sector where the error
occurred. The Command Block Registers contain the cylinder, head, and sector
number of the sector where the error occurred.

The flawed data is pending in the sector buffer.

9.14 Read Verify Sector(s)


This command is identical to the Read Sectors command, except that DRQ is
never set, and no data is transferred to the host. See 10.3 for protocol.

When the requested sectors have been verified, the drive clears BSY and
generates an interrupt. Upon command completion, the Command Block Registers
contain the cylinder, head, and sector number of the last sector verified.

If an error occurs, the verify terminates at the sector where the error
occurs. The Command Block Registers contain the cylinder, head, and sector
number of the sector where the error occurred. The Sector Count Register shall
contain the number of sectors not yet verified.

9.15 Seek

This command initiates a seek to the track and selects the head specified in
the command block. The drive need not be formatted for a seek to execute
properly. See 10.3 for protocol. The drive shall not set DSC=1 until the
action of seeking has completed. The drive may return the interrupt before the
seek is completed.

If another command is issued to the drive while a seek is being executed, the
drive sets BSY=1, waits for the seek to complete, and then begins execution of
the command.

9.16 Set Features

This command is used by the host to establish the following parameters which
affect the execution of certain drive features:

44h Vendor unique length of ECC on Read Long/Write Long commands
55h Disable read look-ahead feature
66h Disable reverting to power on defaults
AAh Enable read look-ahead feature
BBh 4 bytes of ECC apply on Read Long/Write Long commands
CCh Enable reverting to power on defaults

See 10.3 for protocol. If the value in the register is not supported or is
invalid, the drive posts an Aborted Command error.

At power on, or after a hardware reset, the default mode is the same as that
represented by AAh, BBh, and CCh. A setting of 66h allows settings for read
lookahead, number of ECC bytes and multiple count which may have been modified
since power on to remain at the same setting after a software reset.

9.17 Set Multiple Mode

This command enables the drive to perform Read and Write Multiple operations
and establishes the block count for these commands. See 10.3 for protocol.

The Sector Count Register is loaded with the number of sectors per block.
Drives shall support block sizes of 2, 4, 8, and 16 sectors, if their buffer
size is at least 8,192 bytes, and may also support other block sizes. Upon
receipt of the command, the drive sets BSY=1 and checks the Sector Count
Register.

If the Sector Count Register contains a valid value and the block count is
supported, the value is loaded for all subsequent Read Multiple and Write
Multiple commands and execution of those commands is enabled. If a block count
is not supported, an Aborted Command error is posted, and Read Multiple and
Write Multiple commands are disabled.

If the Sector Count Register contains 0 when the command is issued, Read and
Write Multiple commands are disabled.

At power on, or after a hardware reset, the default mode is Read and Write
Multiple disabled. If Disable Default has been set in the Features Register
then the mode remains the same as that last established prior to a software
reset, otherwise it reverts to the default of disabled.

9.18 Sleep

This command is the only way to cause the drive to enter Sleep Mode. The drive
is spun down, and when it is stopped, BSY is cleared, an interrupt is
generated, and the interface becomes inactive.

The only way to recover from Sleep mode without a reset or power on, is for
the host to issue a software reset.

A drive shall not power on in Sleep Mode nor remain in Sleep Mode following a
reset sequence. If the drive is already spun down, the spin down sequence is
not executed.

9.19 Standby

This command causes the drive to enter the Standby Mode. See 10.3 for
protocol. The drive may return the interrupt before the transition to Standby
Mode is completed.


If the drive is already spun down, the spin down sequence is not executed.

If the Sector Count Register is non-zero then the automatic power down
sequence shall be enabled and the timer will begin counting down when the
drive returns to Idle mode. If the Sector Count Register is zero then the
automatic power down sequence shall be disabled.

9.20 Standby Immediate

This command causes the drive to enter the Standby Mode. See 10.3 for
protocol. The drive may return the interrupt before the transition to Standby
Mode is completed.

If the drive is already spun down, the spin down sequence is not executed.

9.21 Write Buffer

This command enables the host to overwrite the contents of the drive's sector
buffer with any data pattern desired. See 10.2 for protocol.

The Read Buffer and Write Buffer commands shall be synchronized within the
drive such that sequential Write Buffer and Read Buffer commands access the
same 512 bytes within the buffer.

9.22 Write DMA

This command executes in a similar manner to Write Sectors except for the
following:

- the host initializes a slave-DMA channel prior to issuing the command
- data transfers are qualified by DMARQ and are performed by the slave-DMA
channel
- the drive issues only one interrupt per command to indicate that data
transfer has terminated and status is available.

Any error encountered during Write DMA execution results in the termination of
data transfer. The drive issues an interrupt to indicate that data transfer
has terminated and status is available in the Error Register. The error
posting is the same as that of the Write Sectors command.

9.23 Write Multiple Command

This command is similar to the Write Sectors command. The drive sets BSY
within 400 nsec of accepting the command, and interrupts are not presented on
each sector but on the transfer of a block which contains the number of
sectors defined by Set Multiple.

Command execution is identical to the Write Sectors operation except that the
number of sectors defined by the Set Multiple command are transferred without
intervening interrupts. DRQ qualification of the transfer is required only at
the start of the data block, not on each sector.

The block count of sectors to be transferred without intervening interrupts is
programmed by the Set Multiple Mode command, which shall be executed prior to
the Read Multiple command.

When the Write Multiple command is issued, the Sector Count Register contains
the number of sectors (not the number of blocks or the block count) requested.


If the number of requested sectors is not evenly divisible by the block count,
as many full blocks as possible are transferred, followed by a final, partial
block transfer. The partial block transfer is for n sectors, where

n = Remainder (Sector Count / Block Count)

If the Write Multiple command is attempted before the Set Multiple Mode
command has been executed or when Write Multiple commands are disabled, the
Write Multiple operation shall be rejected with an aborted command error.

Disk errors encountered during Write Multiple commands are posted after the
attempted disk write of the block or partial block transferred. The Write
command ends with the sector in error, even if it was in the middle of a
block. Subsequent blocks are not transferred in the event of an error.
Interrupts are generated when DRQ is set at the beginning of each block or
partial block.

The contents of the Command Block Registers following the transfer of a data
block which had a sector in error are undefined. The host should retry the
transfer as individual requests to obtain valid error information.

9.24 Write Same

This command executes in a similar manner to Write Sectors except that only
one sector of data is transferred. The contents of the sector are written to
the medium one or more times.

NOTE: The Write Same command allows for initialization of part or all of the
medium to the specified data with a single command.

If the Features Register is 22h, the drive shall write that part of the medium
specified by the sector count, sector number, cylinder and drive/head
registers. If the Features Register contains DDh, the drive shall initialize
all the user accessible medium. If the register contains a value other than
22h or DDh, the command shall be rejected with an aborted command error.

The drive issues an interrupt to indicate that the command is complete. Any
error encountered during execution results in the termination of the write
operation. Status is available in the Error Register if an error occurs. The
error posting is the same as that of the Write Sectors command.

9.25 Write Long

This command is similar to the Write Sectors command except that it writes the
data and the ECC bytes directly from the sector buffer; the drive does not
generate the ECC bytes itself. Only single sector Write Long operations are
supported.

The transfer of the ECC bytes shall be 8-bits wide.

9.26 Write Sector(s)

This command writes from 1 to 256 sectors as specified in the Sector Count
Register (a sector count of zero requests 256 sectors), beginning at the
specified sector. See 10.1 for the DRQ, IRQ and BSY protocol on data
transfers.

If the drive is not already on the desired track, an implied seek is
performed. Once at the desired track, the drive searches for the appropriate
ID field.

If retries are disabled and two index pulses have occurred without error free
reading of the requested ID, an ID Not Found error is posted.

If retries are enabled, up to a vendor specific number of attempts may be made
to read the requested ID before posting an error.

If the ID is read correctly, the data loaded in the buffer is written to the
data field of the sector, followed by the ECC bytes. Upon command completion,
the Command Block Registers contain the cylinder, head, and sector number of
the last sector written.

If an error occurs during a write of more than one sector, writing terminates
at the sector where the error occurs. The Command Block Registers contain the
cylinder, head, and sector number of the sector where the error occurred. The
host may then read the command block to determine what error has occurred, and
on which sector.

9.27 Write Verify

This command is similar to the Write Sectors command, except that each sector
is verified immediately after being written. The verify operation is a read
without transfer and a check for data errors. Any errors encountered during
the verify operation are posted. Multiple sector write verify commands write
all the requested sectors and then verify all the requested sectors before
generating the final interrupt.

10. Protocol Overview

Commands can be grouped into different classes according to the protocols
followed for command execution. The command classes with their associated
protocols are defined below.

For all commands, the host first checks if BSY=1, and should proceed no
further unless and until BSY=0. For most commands, the host will also wait for
DRDY=1 before proceeding. Those commands shown with DRDY=x can be executed
when DRDY=0.

Data transfers may be accomplished in more ways than are described below, but
these sequences should work with all known implementations of ATA drives.

10.1 PIO Data In Commands

This class includes:

- Identify Drive
- Read Buffer
- Read Long
- Read Sector(s)

Execution includes the transfer of one or more 512 byte (>512 bytes on Read
Long) sectors of data from the drive to the host.

a) The host writes any required parameters to the Features, Sector Count,
Sector Number, Cylinder and Drive/Head registers.
b) The host writes the command code to the Command Register.
c) The drive sets BSY and prepares for data transfer.
d) When a sector of data is available, the drive sets DRQ and clears BSY
prior to asserting INTRQ.
e) After detecting INTRQ, the host reads the Status Register, then reads one
sector of data via the Data Register. In response to the Status Register
being read, the drive negates INTRQ.
f) The drive clears DRQ. If transfer of another sector is required, the drive
also sets BSY and the above sequence is repeated from d).

10.1.1 PIO Read Command

+- a) -+-- b) -+ +- e) -+--------+ +- e) -+--------+
|Setup | Issue | | Read |Transfer| | Read |Transfer|
| |Command| |Status| Data |:::::::|Status| Data |
+------+-------+ +------+--------+ +------+--------+
|BSY=0 | |BSY=1 |BSY=0 | |BSY=1 |BSY=0 | |BSY=1
|DRDY=1 | | | | | |
|DRQ=1 | |DRQ=0 |DRQ=1 | |DRQ=0
|Assert|Negate | |Assert|Negate
INTRQ INTRQ INTRQ INTRQ

If Error Status is presented, the drive is prepared to transfer data, and it
is at the host's discretion that the data is transferred.

10.1.2 PIO Read Aborted Command

+- a) -+-- b) -+ +- e) -+
|Setup | Issue | | Read |
| |Command| |Status|
+------+-------+ +------+
|BSY=0 | |BSY=1 |BSY=0 |
|DRDY=1 | |
|DRQ=1 |DRQ=0
|Assert|Negate
INTRQ INTRQ

Although DRQ=1, there is no data to be transferred under this condition.

10.2 PIO Data Out Commands

This class includes:

- Format
- Write Buffer
- Write Long
- Write Sector(s)

Execution includes the transfer of one or more 512 byte (>512 bytes on Write
Long) sectors of data from the drive to the host.

a) The host writes any required parameters to the Features, Sector Count,
Sector Number, Cylinder and Drive/Head registers.
b) The host writes the command code to the Command Register.
c) The drive sets DRQ when it is ready to accept the first sector of data.
d) The host writes one sector of data via the Data Register.
e) The drive clears DRQ and sets BSY.
f) When the drive has completed processing of the sector, it clears BSY and
asserts INTRQ. If transfer of another sector is required, the drive also
sets DRQ.
g) After detecting INTRQ, the host reads the Status Register.
h) The drive clears the interrupt.
i) If transfer of another sector is required, the above sequence is repeated
from d).

10.2.1 PIO Write Command

+- a) -+-- b) -+ +--------+ +- e) -+--------+ +- e) -+
|Setup | Issue | |Transfer| | Read |Transfer| | Read |
| |Command| | Data | |Status| Data |:::::::|Status|
+------+-------+ +--------+ +------+--------+ +------+
|BSY=0 | |BSY=1 |BSY=0 |BSY=1 |BSY=0 | |BSY=1 |BSY=0 |
|DRDY=1 | | | | | | |
|DRQ=1 |DRQ=0 |DRQ=1 | |DRQ=0 | |
| | |Assert|Negate | |Assert|Negate
INTRQ INTRQ INTRQ INTRQ

10.2.2 PIO Write Aborted Command

+- a) -+-- b) -+ +- e) -+
|Setup | Issue | | Read |
| |Command| |Status|
+------+-------+ +------+
|BSY=0 | |BSY=1 |BSY=0 |
|DRDY=1 | |
| |Assert|Negate
INTRQ INTRQ

10.3 Non-Data Commands

This class includes:

- Execute Drive Diagnostic (DRDY=x)
- Idle
- Initialize Drive Parameters (DRDY=x)
- Read Power Mode
- Read Verify Sector(s)
- Recalibrate
- Seek
- Set Features
- Set Multiple Mode
- Standby

Execution of these commands involves no data transfer.

a) The host writes any required parameters to the Features, Sector Count,
Sector Number, Cylinder and Drive/Head registers.
b) The host writes the command code to the Command Register.
c) The drive sets BSY.
d) When the drive has completed processing, it clears BSY and asserts INTRQ.
g) The host reads the Status Register.
h) The drive negates INTRQ.

10.4 Miscellaneous Commands

This class includes:

- Read Multiple
- Sleep
- Write Multiple
- Write Same

The protocol for these commands is contained in the individual command
descriptions.

10.5 DMA Data Transfer Commands (Optional)

This class comprises:

- Read DMA
- Write DMA

Data transfers using DMA commands differ in two ways from PIO transfers:

- data transfers are performed using the slave-DMA channel
- no intermediate sector interrupts are issued on multi-sector commands

Initiation of the DMA transfer commands is identical to the Read Sector or
Write Sector commands except that the host initializes the slave-DMA channel
prior to issuing the command.

The interrupt handler for DMA transfers is different in that:

- no intermediate sector interrupts are issued on multi-sector commands
- the host resets the DMA channel prior to reading status from the drive.

The DMA protocol allows high performance multi-tasking operating systems to
eliminate processor overhead associated with PIO transfers.

a) Command Phase
1) Host initializes the slave-DMA channel
2) Host updates the Command Block Registers
3) Host writes command code to the Command Register
b) Data Phase - the register contents are not valid during a DMA Data Phase.
1) The slave-DMA channel qualifies data transfers to and from the drive
with DMARQ
c) Status Phase
1) Drive generates the interrupt to the host
2) Host resets the slave-DMA channel
3) Host reads the Status Register and Error Register

10.5.1 Normal DMA Transfer

+--------------+-------+ +---------------------+ +---------+------+
|Initialize DMA|Command| | DMA Data Transfer | |Reset DMA|Status|
+--------------+-------+ +---------------------+ +---------+------+
|BSY=0 |BSY=1 |BSY=x |BSY=1 |BSY=0
|DRQ=x |nIEN=0

10.5.2 Aborted DMA Transfer

+--------------+-------+ +-------------+ +---------+------+
|Initialize DMA|Command| | DMA Data | |Reset DMA|Status|
+--------------+-------+ +-------------+ +---------+------+
|BSY=0 |BSY=1 |BSY=x |BSY=1 |BSY=0
|DRQ=1 |nIEN=0

10.5.3 Aborted DMA Command

+--------------+-------+ +---------+------+
|Initialize DMA|Command| |Reset DMA|Status|
+--------------+-------+ +---------+------+
|BSY=0 |BSY=1 |BSY=1 |BSY=0
|nIEN=0

11. Timing

11.1 Deskewing

The host shall provide cable deskewing for all signals originating from the
controller. The drive shall provide cable deskewing for all signals
originating at the host.

11.2 Symbols

Certain symbols are used in the timing diagrams. These symbols and their
respective definitions are listed below.

/ or \ - signal transition (asserted or negated) *
< or > - data transition (asserted or negated)
XXXXXX - undefined but not necessarily released
. . . - the "other" condition if a signal is shown with no change
#n - used to number the sequence in which events occur e.g. #a, #b
_ _ __
__/_ _/ - a degree of uncertainty as to when a signal may be asserted

__ _ _
\_ _\__ - a degree of uncertainty as to when a signal may be negated

* All signals are shown with the Asserted condition facing to the top of
the page. The negated condition is shown towards the bottom of the page
relative to the asserted condition.

11.3 Terms

The interface uses a mixture of negative and positive signals for control and
data. The terms asserted and negated are used for consistency and are
independent of electrical characteristics.

In all timing diagrams, the lower line indicates negated, and the upper line
indicates asserted e.g. the following illustrates the representation of a
signal named TEST going from negated to asserted and back to negated, based on
the polarity of the signal.

Assert Negate
| |
Bit Setting=1 |__________|
Bit Setting=0 TEST _____/ \_______

Assert Negate
| |
Bit Setting=0 |__________|
Bit Setting=1 TEST- _____/ \_______

11.4 Data Transfers

Figure 11-1 defines the relationships between the interface signals for both
16-bit and 8-bit data transfers.

|<------------ t0 -------------------->|
__________________________________________ |
Address Valid *1 ...../ \________
|<-t1->| ->| t9 |<-
->|t7|<- |<----------- t2 ------------->| ->|t8|<-
| | |______________________________| | |_____
DIOR-/DIOW- ____________/ \_______/
| | |_ _ _ _ _ _ _ _ _ _ _____________ |
Write Data Valid *2__________/_ _ _ _ _ _ _ _ _ _/ \__________
| | | |<--t3---->| |
| | | ->|t4|<- |
| | |_ _ _ _ _ _ _ _ _ _ _ ___________ |
Read Data Valid *2__________/_ _ _ _ _ _ _ _ _ _ _/ | \__________
| | | |<--t5-->| | |
| | | ->|t6|<- |
| | | | | |
| |__________________________________________|
IOCS16- ________/ \_____

*1 Drive Address consists of signals CS1FX-, CS3FX- and DA2-0
*2 Data consists of DD0-15 (16-bit) or DD0-7 (8-bit)

+------------------------------------------+-------+-------+-------+
| PIO | Mode 0| Mode 1| Mode 2|
| Timing Parameters | nsec | nsec | nsec |
+----+------------------------------------------+-------+-------+-------+
| t0 | Cycle Time (Min) | 600 | 383 | 240 |
| t1 | Address Valid to DIOR-/DIOW- Setup (Min) | 70 | 50 | 30 |
| t2 | DIOR-/DIOW- 16-bit (Min) | 165 | 125 | 100 |
| | Pulse Width 8-bit (Min) | 290 | 290 | 290 |
| t3 | DIOW- Data Setup (Min) | 60 | 45 | 30 |
| t4 | DIOW- Data Hold (Min) | 30 | 20 | 15 |
| t5 | DIOR- Data Setup (Min) | 50 | 35 | 20 |

| t6 | DIOR- Data Hold (Min) | 5 | 5 | 5 |
| t7 | Addr Valid to IOCS16- Assertion (Max) | 90 | 50 | 40 |
| t8 | Addr Valid to IOCS16- Negation (Max) | 60 | 45 | 30 |
| t9 | DIOR-/DIOW- to Address Valid Hold (Min) | 20 | 15 | 10 |
+----+------------------------------------------+-------+-------+-------+

FIGURE 11-1: PIO DATA TRANSFER TO/FROM DRIVE

___________________________________
DIOR-/DIOW- __________/ \______________
|
|<- tA ->|<--- tB ---->|
___________________| |_____________________
IORDY \___________________/

Label Description Min Max Units

tA IORDY Setup time - 35 nsecs
tB IORDY Pulse Width - 1,250 nsecs

WARNING: The use of IORDY for data transfers is a system integration issue
which requires control of both ends of the cable.

FIGURE 11-2: IORDY TIMING REQUIRMENTS

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

|<----------------------- t0 ---------------------->|
____________ _______
DMARQ ___/ \______________________________________/ |
|<- tC ->| |
|_____________________________________________ |___
DMACK- _______/ \_____/
|<--- tI --->|________________|<----- tJ -----| |
DIOR-/DIOW- ____________________/ \_________________________
| | | |
| |<------ tD ---->| |
Read | ______________ |
DD0-15 -------------------------------<______________>----------------
| |<-- tE -->| |<- tF ->| |
Write | _________________________ |
DD0-15 --------------------------<_________________________>-----------
| | | | |
| |<-- tG -->|<-- tH -->| |

+----------------------------------+-------+-------+-------+
| DMA | Mode 0| Mode 1| Mode 2|
| Timing Parameters | nsec | nsec | nsec |
+----+----------------------------------+-------+-------+-------+
| t0 | Cycle Time (Min) | 960 | 480 | 240 |
| tC | DMACK to DMREQ Delay (Max) | 200 | 100 | 80 |
| tD | DIOR-/DIOW- 16-bit (Min) | 480 | 240 | 120 |
| tE | DIOR- Data Setup (Min) | 250 | 150 | 50 |
| tF | DIOR- Data Hold (Min) | 5 | 5 | 5 |
| tG | DIOW- Data Setup (Min) | 250 | 100 | 35 |
| tH | DIOW- Data Hold (Min) | 50 | 30 | 20 |
| tI | DMACK to DIOR-/DIOW- Setup (Min) | 0 | 0 | 0 |
| tJ | DIOR-/DIOW- to DMACK Hold (Min) | 0 | 0 | 0 |
+----+----------------------------------+-------+-------+-------+

FIGURE 11-3: DMA DATA TRANSFER

11.5 Power On and Hard Reset

______
RESET- _____/ \_____________________________________________________
|<-tM->|
| | Drive 0
_ _ _ _ _ _ _ _______ _ _ _ _ _ _ _ _ _ _ _ _ _|
BSY _ _ _ _ _ _ _/ \_ _ _ _ _ *1 _ _ _ _ _ _\________________
->|tN|<-
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
DASP- _ _ _ _ _ _ _ _\_______/_ _ _ _ *2 _ _ _ _ _ _ _ _ _ _\=== *3 ==
->| tP |<- | |_ _ _ __________
Control Registers_______________________________________/_ _ _ /
| | |
| | | Drive 1
_ _ _ _ _ _ _ _ _________________________________|
BSY _ _ _ _ _ _ _ _/ \________________
_ _ _ _ _ _ _ _ _ _ ______ _ _ _ _ _
PDIAG- _ _ _ _ _ _ _ _ _ _\____________________________/ \_ _ _ _ _
| | | |<----------- tQ -------->|
_ _ _ _ _ _ _ _ _ _________________________ _ _ _
DASP- _ _ _ _ _ _ _ _ _\_____/ \ _ _ _\=== *3 ==
|<- tR ->|<------------ tS -------------->|
_ _ _ __________
Control Registers_______________________________________/_ _ _ /

*1 Drive 0 can set BSY=0 if Drive 1 not present
*2 Drive 0 can use DASP- to indicate it is active if Drive 1 is not
present
*3 DASP- can be asserted to indicate that the drive is active
+-------------------+------------+
| Label | Units |
+-------------------+------------+
| tM (Min) | 25 usec |
| tN (Max) | 400 nsec |
| tP (Max) | 1 msec |
| tQ (Max) | 30 secs |
| tR Drive 0 (Max) | 450 msec |
| tR Drive 1 (Max) | 400 msec |
| tS (Max) | 30.5 secs |
+-------------------+------------+

FIGURE 11-4 RESET SEQUENCE

Annex A: Diagnostic and Reset Considerations
(informative).

This annex describes the following timing relationships during:

a) Power On and Hardware Resets
- One drive
- Two drives
b) Software Reset
- One drive
- Two drives
c) Diagnostic Command Execution
- One drive
- Two drives
- Two drives - Drive 1 failed

The timing assumes the following:

o DASP- is asserted by Drive 1 and received by Drive 0 at power-on or hardware
reset to indicate the presence of Drive 1. At all other times it is asserted
by Drive 0 and Drive 1 to indicate when a drive is active.
o PDIAG- is asserted by Drive 1 and detected by Drive 0. It is used by Drive 1
to indicate to Drive 0 that it has completed diagnostics and is ready to
accept commands from the Host (BSY bit is cleared). This does not indicate
that the drive is ready, only that it can accept commands. This line may
remain asserted until the next reset occurs or an Execute Diagnostic
command is received.
o Unless indicated otherwise, all times are relative to the event that
triggers the operation (RESET-, SRST=1, Execute Diagnostic Command).

A.1 Power On and Hardware Resets

A.1.1 Power On and Hardware Resets - One Drive

- Host asserts RESET- for a minimum of 25 usec.
- Drive 0 sets BSY within 400 nsecs after RESET- is negated.
- Drive 0 negates DASP- within 1 msec after RESET- negated.
- Drive 0 performs hardware initialization
- Drive 0 may revert to its default condition
- Drive 0 waits 1 msec then samples for at least 450 msec for DASP- to be
asserted from Drive 1.
- Drive 0 clears BSY when ready to accept commands (within 31 seconds).

A.1.2 Power On and Hardware Resets - Two Drives

- Host asserts RESET- for a minimum of 25 usec.
- Drive 0 and Drive 1 set BSY within 400 nsec after RESET- negated.
- DASP- is negated within 1 msec after RESET- is negated.

A.1.2.1 Drive 1

- Drive 1 negates PDIAG- before asserting DASP-.
- Drive 1 asserts DASP- within 400 msecs after RESET- (to show presence).
- Drive 1 performs hardware initialization and executes its internal
diagnostics.
- Drive 1 may revert to its default condition
- Drive 1 posts diagnostic results to the Error Register
- Drive 1 clears BSY when ready to accept commands.
- Drive 1 asserts PDIAG- to indicate that it is ready to accept commands
(within 30 seconds from RESET-).
- Drive 1 negates DASP- after the first command is received or negates DASP-
if no command is received within 30 seconds after RESET-.

A.1.2.2 Drive 0

- Drive 0 performs hardware initialization and executes its internal
diagnostics.
- Drive 0 may revert to its default condition
- Drive 0 posts diagnostic results to the Error Register
- After 1 msec, Drive 0 waits at least 450 msec for DASP- to be asserted (from
Drive 1). If DASP- is not asserted, no Drive 1 is present (see POWER- ON
RESET - One Drive operation).
- Drive 0 waits up to 31 seconds for Drive 1 to assert PDIAG-. If PDIAG- is not
asserted, Drive 0 sets Bit 7=1 in the Error Register.
- Drive 0 clears BSY when ready to accept commands (within 31 seconds).

A.2 Software Reset

A.2.1 Software Reset - One Drive

- Host sets SRST=1 in the Device Control Register.
- Drive 0 sets BSY within 400 nsec after detecting that SRST=1.
- Drive 0 performs hardware initialization and executes its internal
diagnostics.
- Drive 0 may revert to its default condition.
- Drive 0 posts diagnostic results to the Error Register.
- Drive 0 clears BSY when ready to accept commands (within 31 seconds).

A.2.2 Software Reset - Two Drives

- Host sets SRST=1 in the Device Control Register.
- Drive 0 and Drive 1 set BSY within 400 nsec after detecting that SRST=1.
- Drive 0 and Drive 1 perform hardware initialization.
- Drive 0 and Drive 1 may revert to their default condition.

A.2.2.1 Drive 1

- Drive 1 negates PDIAG- within 1 msec.
- Drive 1 clears BSY when ready to accept commands.
- Drive 1 asserts PDIAG- to indicate that it is ready to accept commands
(within 30 seconds).

A.2.2.2 Drive 0

- Drive 0 waits up to 31 seconds for Drive 1 to assert PDIAG-.
- Drive 0 clears BSY when ready to accept commands (within 31 seconds).

A.3 Diagnostic Command Execution

A.3.1 Diagnostic Command Execution - One Drive (Passed)

- Drive 0 sets BSY within 400 nsec after the Execute Diagnostic command was
received.
- Drive 0 performs hardware initialization and internal diagnostics.
- Drive 0 resets Command Block registers to default condition.
- Drive 0 posts diagnostic results to the Error Register
- Drive 0 clears BSY when ready to accept commands (within 6 seconds).

A.3.2 Diagnostic Command - Two Drives (Passed)

- Drive 0 and Drive 1 set BSY within 400 nsec after the Execute Diagnostic
command was received.

A.3.2.1 Drive 1

- Drive 1 negates PDIAG- within 1 msec after command received.
- Drive 1 performs hardware initialization and internal diagnostics.
- Drive 1 resets the Command Block registers to their default condition.
- Drive 1 posts diagnostic results to the Error Register
- Drive 1 clears BSY when ready to accept commands.
- Drive 1 asserts PDIAG- to indicate that it is ready to accept commands
(within 5 seconds).

A.3.2.2 Drive 0

- Drive 0 performs hardware initialization and internal diagnostics.
- Drive 0 resets the Command Block registers to their default condition.
- Drive 0 waits up to <5 seconds for Drive 1 to assert PDIAG-.
- Drive 0 posts diagnostic results to the Error Register
- Drive 0 clears BSY when ready to accept commands (within 6 seconds).

A.3.3 Diagnostic Command Execution - One Drive (Failed)

- Drive 0 sets BSY within 400 nsec after Diagnostic command received.
- Drive 0 performs hardware initialization and internal diagnostics.
- Drive 0 resets Command Block registers to default condition.
- Drive 0 posts a Diagnostic Code to the Error Register indicating a failure.
- Drive 0 clears BSY when ready to accept commands (within 6 seconds)

A.3.4 Diagnostic Command Execution - Two Drives (Drive 1 Failed)

- Drive 0 and Drive 1 set BSY within 400 nsec after Diagnostic command
received.

A.3.4.1 Drive 1

- Drive 1 negates PDIAG- within 1 msec after command received.
- Drive 1 performs hardware initialization and internal diagnostics.
- Drive 1 resets the Command Block registers to their default condition.
- Drive 1 posts a Diagnostic Code to the Error Register indicating failure.
- Drive 1 clears BSY.
- Drive 1 does not assert PDIAG-, indicating that it failed diagnostics.

A.3.4.2 Drive 0

- Drive 0 performs hardware initialization and internal diagnostics.
- Drive 0 resets the Command Block registers to their default condition.
- Drive 0 waits 6 seconds for Drive 1 to assert PDIAG- but PDIAG- is not
asserted by Drive 1.
- Drive 0 posts a Diagnostic Code to the Error Register setting Bit 7=1 to
indicate that Drive 1 failed diagnostics.
- Drive 0 clears BSY when ready to accept commands (within 6 seconds).

NOTE: The 6 seconds referenced above is a host-oriented value.

Annex B: Diagnostic and Reset Considerations
(informative).

B.1 Power on and hardware reset (RESET-)

DASP- is read by Drive 0 to determine if Drive 1 is present. If Drive 1 is
present Drive 0 will read PDIAG- to determine when it is valid to clear BSY and
whether Drive 1 has powered on or reset without error, otherwise Drive 0 clears
BSY whenever it is ready to accept commands. Drive 0 may assert DASP- to
indicate drive activity.

B.2 Software reset

If Drive 1 is present Drive 0 will read PDIAG- to determine when it is valid to
clear BSY and whether Drive 1 has reset without any errors, otherwise Drive 0
will simply reset and clear BSY. DASP- is asserted by Drive 0 (and Drive 1 if
it is present) in order to indicate drive active.

B.3 Drive Diagnostic Command

If Drive 1 is present, Drive 0 will read PDIAG- to determine when it is valid to
clear BSY and if Drive 1 passed or failed the Execute Drive Diagnostic command,
otherwise Drive 0 will simply execute its diagnostics and then clear BSY.
DASP- is asserted by Drive 0 (and Drive 1 if it is present) in order to indicate
the drive is active.

B.4 Truth Table

In all the above cases: Power on, RESET-, software reset, and the Execute
Drive Diagnostics command the Drive 0 Error Register is calculated as follows:

Drive 1 PDIAG- Drive 0 Error
Present? Asserted? Passed Register

Yes Yes Yes 01h
Yes Yes No 0xh
Yes No Yes 81h
Yes No No 8xh
No (not read) Yes 01h
No (not read) No 0xh

Where x indicates the appropriate Diagnostic Code for the Power on, RESET-,
software reset, or drive diagnostics error.

B.5 Power On or Hardware Reset Algorithm

1) Power on or hardware reset
2) The hardware should automatically do the following:
a) Set up the hardware to post both Drive 0 and Drive 1 status
b) Set the Drive 0 Status Register to 80h (set BSY and clear
all the other status bits)
c) Set the Drive 1 Status Register to 80h (set BSY and clear all
the other status bits)
3) Read the single Drive 0/Drive 1 jumper and note its state
4) Perform any remaining time critical hardware initialization including
starting the spin up of the disk if needed
5) If Drive 1
a) Negate the PDIAG- signal
b) Set up PDIAG- as an output
c) Assert the DASP- output
d) Set up DASP- as an output if necessary
e) Set up the hardware so it posts Drive 1 status only and
continue to post 80h for Drive 1 status
NOTE: all this must happen within 400 msec after power on or RESET-
If Drive 0
a) Set up PDIAG- as an input
b) Release DASP- and set up DASP- as an input
c) Test DASP- for 450 msec or until DASP- is asserted by Drive 1
d) If DASP- is asserted within 450 msec
i) Note that Drive 1 is present
ii) Set up the hardware so it posts Drive 0 status only
and continue to post 80h for the Drive 0 status
If DASP- is not asserted within 450 msec
i) note that Drive 1 is not present
e) Assert DASP- to indicate drive activity
6) Complete all the hardware initialization needed to get the drive ready,
including:
a) Set the Sector Count Register to 01h
b) Set the Sector Number Register to 01h
c) Set the Cylinder Low Register to 00h
d) Set the Cylinder High Register to 00h
e) Set the Drive/Head Register to 00h
7) If Drive 1 and power on, or RESET- is valid
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 Status Register to 00h
c) Assert PDIAG-
NOTE: All this must happen within 5 seconds of power on or the
negation of RESET-
If Drive 1 and power on or RESET- bad
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 Status Register to 00h
NOTE: All this must happen within 5 seconds of power on or the
negation of RESET-
If Drive 0, power on or RESET- valid, and a Drive 1 is present
a) Test PDIAG- for 6 seconds or until PDIAG- is asserted by Drive 1
b) If PDIAG- is asserted within 6 seconds
i) Set the Error Register to Diagnostic Code 01h
c) If PDIAG- is not asserted within 6 seconds
i) Set the Error Register to 81h
d) Set the Drive 0 Status Register to 00h
If Drive 0, power on or RESET- bad, and a Drive 1 is present
a) Test PDIAG- for 6 seconds or until PDIAG- is asserted by
Drive 1
b) If PDIAG- is asserted within 6 seconds
i) Set the Error Register to the appropriate Diagnostic Code

c) If PDIAG- is not asserted within 6 seconds
i) Set the Error Register to 80h + the appropriate code
d) Set the Drive 0 Status Register to 00h
If Drive 0, power on or RESET- valid, and no Drive 1 is present
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 00h
If Drive 0, power on or RESET- bad, and no Drive 1 is present
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 00h
8) Finish spin up if needed
9) If Drive 1
a) Set the Drive 1 Status Register to 50h
b) Negate DASP- if a command is not received within 30 seconds
If Drive 0 and a Drive 1 is present
a) Set the Drive 0 Status Register to 50h
b) Negate DASP-
If Drive 0 and no Drive 1 is present
a) Leave the Drive 1 Status Register 00h
b) Set the Drive 0 Status Register to 50h
c) Negate DASP-

B.6 Software Reset Algorithm

1) The software reset bit is set
2) If Drive 1
a) The hardware should set BUSY in the Drive 1 Status Register
b) Negate the PDIAG- signal
NOTE: this must happen within 1 msec of the software reset
If Drive 0 and Drive 1 is present
a) The hardware should set BUSY in the Drive 0 Status Register
If Drive 0 and there is no Drive 1 the hardware should:
a) Set BUSY in the Drive 0 Status Register
b) Set the Drive 1 Status Register to 80h
3) Assert DASP-
4) Finish all the hardware initialization needed to place the drive in reset
5) Wait for the software reset bit to clear
6) Finish all hardware initialization needed to get the drive ready
to receive any type of command from the host including:
a) Set the Sector Count Register to 01h
b) Set the Sector Number Register to 01h
c) Set the Cylinder Low Register to 00h
d) Set the Cylinder High Register to 00h
e) Set the Drive/Head Register to 00h
7) If Drive 1 and reset valid
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 Status Register to 50h
c) Assert PDIAG-
NOTE: All this must happen within 5 seconds of the clearing of
the software reset bit

If Drive 1 and reset bad
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 Status Register to 50h
NOTE: All this must happen within 5 seconds of the clearing of
the software reset bit
If Drive 0, reset valid, and a Drive 1 is present
a) Test PDIAG- for 6 seconds or until PDIAG- is asserted by
Drive 1
b) If PDIAG- is asserted within 6 seconds
i) Set the Error Register to Diagnostic Code 01h
c) If PDIAG- is not asserted within 6 seconds
i) Set the Error Register to 81h
d) Set the Drive 0 Status Register to 50h
If Drive 0, reset bad, and a Drive 1 is present
a) Test PDIAG- for 31 seconds or until PDIAG- is asserted by
Drive 1
b) If PDIAG- is asserted within 31 seconds
i) Set the Error Register to the appropriate Diagnostic Code

c) If PDIAG- is not asserted within 31 seconds
i) Set the Error Register to 80h + the appropriate code
d) Set the Drive 0 Status Register to 50h
If Drive 0, reset valid, and no Drive 1 is present
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 50h
If Drive 0, reset bad, and no Drive 1 is present
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 50h

B.7 Diagnostic Command Algorithm

1) The diagnostics command is received
2) If Drive 1
a) The hardware should set BUSY in the Drive 1 Status Register
b) Negate the PDIAG- signal
NOTE: this must happen within 1 msec after command acceptance
If Drive 0 and Drive 1 is present
a) The hardware should set BUSY in the Drive 0 Status Register
If Drive 0 and there is no Drive 1 the hardware should
a) Set BUSY in the Drive 0 Status Register
b) Set BUSY in the Drive 1 Status Register
3) Assert DASP-
4) Perform all the drive diagnostics and note their results
5) Finish all the hardware initialization needed to get the drive ready
to receive any type of command from the host including:
a) Set the Sector Count Register to 01h
b) Set the Sector Number Register to 01h
c) Set the Cylinder Low Register to 00h
d) Set the Cylinder High Register to 00h
e) Set the Drive/Head Register to 00h
6) If Drive 1 and passed
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 status to 50h
c) Assert PDIAG-
NOTE: All this must happen within 5 seconds of the acceptance
of the diagnostic command
If Drive 1 and did not pass
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 status to 50h
NOTE: All this must happen within 5 seconds of the acceptance
of the diagnostic command
If Drive 0, passed, and a Drive 1 is present
a) Test PDIAG- for 6 seconds or until PDIAG- is asserted by
Drive 1
b) If PDIAG- is asserted within 6 seconds
i) Set the Error Register to Diagnostic Code 01h
c) If PDIAG- is not asserted within 6 seconds
i) Set the Error Register to 81h
d) Set the Drive 0 status to 50h
e) Issue interrupt to the host
If Drive 0, did not pass, and a Drive 1 is present
a) Test PDIAG- for 6 seconds or until PDIAG- is asserted by Drive 1
b) If PDIAG- is asserted within 6 seconds
i) Set the Error Register to the appropriate Diagnostic Code

c) If PDIAG- is not asserted within seconds
i) Set the Error Register to 80h + the appropriate code
d) Set the Drive 0 Status Register to 50h
e) Issue interrupt to the host
If Drive 0, passed, and no Drive 1 is present
a) Set the Error Register to Diagnostic Code 01h
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 50h
d) Issue interrupt to the host
If Drive 0, did not pass, and no Drive 1 is present
a) Set the Error Register to the appropriate Diagnostic Code
b) Set the Drive 1 Status Register to 00h
c) Set the Drive 0 Status Register to 50h
d) Issue interrupt to the host