Emulex MD21/S2 Technical Manual

MD21/S2 DISK CONTROLLER

TECHNICAL MANUAL

( SCSI-COMPATIBLE)

EM ULEX

3545 Harbor Boulevard

Costa Mesa, California 92626

(714) 662-5600 TWX 910-595-2521

MD2151003-00 Rev E

March, 1988

WARNING

This equipment generates, uses and can radiate

radio frequency energy, and if not installed and

used in accordance with the technical manual, may

cause interference to radio communications. It

has been tested and found to comply with the

limits for a Class B computing device pursuant to

Subpart J of Part 15 of the Federal Communications

Commission (FCC) Rules, which are designed to

provide reasonable protection against such

interference when operating in a residential

installation. However, there is no guarantee that

interference will not occur in a particular

installation.

Emulex is a registered trademark of Emulex Corporation.

IBM PC and IBM PC/XT are registered trademarks of International

Business Machines Incorporated.

Multibus is a registered trademark of Intel Corporation.

The information in this manual is for information purposes only and

is subject to change without notice.

Emulex Corporation assumes no responsibility for any errors which may

appear in the manual.

Printed in U.S.A.

TABLE OF CONTENTS

Section Page

Preface

.................................................

vii

ONE: INTRODUCTION

1.1 OVERVIEW

...

................

1-1

1.2 FEATURES

........................................

1-2

1.3 ORGANIZATION OF THE MANUAL

.

......................

1-3

TWO: GENERAL DESCRIPTION

2.1 INTRODUCTION

.....................................

2-1

2.2 MD21 DISK CONTROLLER OVERVIEW

...................

2-1

2.2.1 PHYSICAL DESCRIPTION

..........................

2-1

2.2.2 FUNCTIONAL OVERVIEW .......... 2-3

2.2.2.1 8031 Microprocessor

.........................

2-5

2.2.2.2 Disk Formatter

..............................

2-5

2.2.2.3 Buffer Controller

...........................

2-5

2.3 SCSI BUS OVERVIEW

...............................

2-6

2.4 ESDI OVERVIEW

...................................

2-8

2.5 COMPATIBILITY

...................................

2-9

2.5.1 SCSI BUS HARDWARE COMPATIBILITY

...............

2-9

2.5.2 ESDI DISK DRIVE COMPATIBILITY

.................

2-9

THREE: DISK CONTROLLER SPECIFICATIONS

3.1 OVERVIEW ............................... 3-1

3.2 GENERAL AND ELECTRICAL SPECIFICATIONS

...........

3-1

3.3 PHYSICAL SPECIFICATIONS

.........................

3-3

3.4 ENVIRONMENTAL SPECIFICATIONS .......... 3-5

FOUR: DISK DRIVE PARAMETERS

4.1 OVERVIEW

.

....................

4-1

4.2 ESDI DISK DRIVE PREPARATION

.....................

4-1

4.2.1 DRIVES SUPPORTED

...............................

4-1

4.2.2 DRIVE PLACEMENT ................ 4-1

4.2.3 DRIVE NUMBERING

...............................

4-1

4.2.4 SPINDLE CONTROL

................................

4-2

4.2.5 DRIVE SECTORING AND OTHER OPTIONS

.............

4-2

4.3 DISK OPERATIONS .................................. 4-5

4.3.1 SECTOR AND TRACK FORMAT OPERATIONS

.......

4-5

4.3.2 GROWN DEFECT LIST OPERATIONS

..................

4-6

Table of Contents iii

FIVE: INSTALLATION

5.1 OVERVIEW

........................................

5-1

5.2 INSPECTION

......................................

5-3

5.3 MD21 CONTROLLER SETUP

...........................

5-3

5.3.1 SWITCH SETTINGS

...............................

5-3

5.3.1.1 SCSI Device Address Selection

(SWl-1 through SWl-3)

.

..................... 5-4

5.3.1.2 Sector Size (SWl-5) 5-5

5.3.1.3 Disable Drive Spin up (SWl-6)

................

5-6

5.3.1.4 Disable Soft Error Reporting (SWl-7) 5-6

5.3.1.5 SCSI Bus Parity Enable (SWl-8) 5-7

5.3.2 SCSI BUS TERMINATION POWER OPTION

.............

5-7

5.3.3 SCSI BUS TERMINATION

..........................

5-8

5.4 MD21 CONTROLLER INSTALLATION

....................

5-8

5.5 FCC COMPLIANCE

..................................

5-11

SIX: CONTROLLER INITIALIZATION AND SELF-TEST PROCEDURES

6.1 OVERVIEW..

.......................................

6-1

6.2 CONTROLLER RESET/POWER UP INITIALIZATION

..........

6-1

6.2.1 SELF-TEST SEQUENCE

.............................

6-1

6.2.2 INITIALIZATION SEQUENCE

........................

6-3

6.3 SELF-TEST MODES

..................................

6-5

6.3.1 NORMAL MODE

....................................

6-5

6.3.2 BURN-IN MODE............ 6-7

6.4 ONLINE DIAGNOSTIC COMMANDS

..............

-.,

......

6-9

SEVEN: INTERFACES

7.1 OVERVIEW

........................................

7-1

7.2 SCSI BUS INTERFACE ............ 7-1

7.2.1 SCSI BUS INTERFACE PHYSICAL DESCRIPTION

.......

7-1

7.2.1.1 Internal Cable Requirements

.................

7-2

7.2.1.2 Shielded Cable Requirements

.................

7-2

7.2.2 SCSI INTERFACE ELECTRICAL DESCRIPTION

.........

7-3

7.2.2.1 Output Signal Characteristics

................

7-3

7.2.2.2 Input Signal Characteristics

.................

7-4

7.2.2.3 Terminator Power (Optional)

.................

7-5

7.2.3 SCSI BUS SIGNALS AND TIMING

...................

7-5

7.2.3.1 SCSI Bus Signals

............................

7-5

7.2.3.2 SCSI Bus Timings

............................

7-9

7.3 ESDI DISK DRIVE INTERFACE

......................

7-13

7.3.1 ESDI INTERFACE ELECTRICAL DESCRIPTION

.........

7-13

7.3.1.1 Output Signal Characteristics

...............

7-13

7.3.1.2 Input Signal Characteristics

................

7-14

7.3.1.3 Termination

.................................

7-14

7.3.1.4 ESDI Signals

................................

7-14

iv Table of Contents

SEVEN: INTERFACES (continued)

7.4 USER PANEL CONNECTION

......

.

...................

7-18

7.4.1 OUTPUTS FROM THE MD21

....

7-19

7.4.2 WRITE-PROTECT INPUTS TO THE MD21

..............

7-19

7.4.3 POWER FAIL DETECT SIGNAL

.....................

7-20

7.5 DC POWER CONNECTION ..........

.......

..........

7-20

APPENDIX A: TROUBLESHOOTING

A. 1 OVERVIEW

.....................

A-l

A.2 PROBLEM IDENTIFICATION

..........................

A-l

A.3 TECHNICAL ASSISTANCE ............................ A-l

A. 4 SERVICE •

......

.................................. A-2

A. 5 SCSI PRODUCT PERFORMANCE REPORT

.................

A-3

APPENDIX B: PROM REMOVAL AND REPLACEMENT

B. l OVERVIEW

......................

.

.................

B—1

B.2 EXCHANGING PROMS ................................. B-l

TABLES

Table Title Page

2- 1 Emulex-Certified ESDI Disk Drives

.............

2-10

3- 1 General and Electrical Specifications

..........

3-1

3-2 Physical Specifications

...............

3-4

3- 3 Environmental Specifications

...................

3-5

4- 1 Recommended Disk Parameters for ESDI Drives

....

4-3

5- 1 DIP Switch Settings, MD21 Controller

...........

5-4

5-2 SCSI Device Address Selection Switches

.........

5-5

5- 3 Disk Drive Cable Requirements

..................

5-11

6- 1 LED Sequences for Self-Test Procedure

..........

6-3

6-2 LED Test Code Descriptions

.

....................

6-6

6-3 MD21 Controller Test Code Descriptions

......

6-8

6-4 MD21 Controller Diagnostic Subcommands

.........

6-9

Table of Contents v

TABLES (continued)

Table Title Page

7-1 SCSI Bus Signals................................ 7-7

7-2 Single-Ended Pin/Signal Assignments at SCSI

Bus Interface

................................

7-8

7-3 Disk Drive Cable Requirements

.......

7-13

7-4 Control Cable Pin Assignments................... 7-16

7-5 Data Cable Pin Assignments...................... 7-17

7-6 Connector J4 Pin Description

...................

7-19

7-7 Power Supply Connections ....................... 7-21

FIGURES

Figure Title Page

2-1 MD21 Disk Controller

...........................

2-2

2-2 MD21 Controller Block Diagram

..................

2-4

2-3 Sample SCSI Bus Configuration................... 2-7

2- 4 Typical Multi-Drive Configuration

..............

2-8

3- 1 MD21 Controller Dimensions...................... 3-5

4- 1 Sector Format for Hard-Sectored Disk Drives

....

4-7

4- 2 Sector Format for Soft-Sectored Disk Drives..... 4-8

5- 1 MD21 Configuration Reference Sheet

.............

5-2

5-2 Sector Size Switch Setting...................... 5-5

5-3 Drive Spin Up Switch Setting

...................

5-6

5-4 Soft Error Reporting Switch Setting............. 5-6

5-5 Parity Enable Switch Setting

...................

5-7

5-6 Installing the MD21 Controller on the

Mounting Bracket

.............................

5-10

5- 7 Connecting the Disk Drive Data and Control

Cables and the SCSI bus to the MD21 Controller 5-10

6- 1 Location of LEDs on the MD21 Controller

........

6-6

7- 1 MD21 Controller Component Locations

............

7-3

7-2 SCSI Bus Signals Termination.................... 7-4

7-3 SCSI Bus Timing Diagram

.................

7-10

7-4 ESDI Control Cable Pin/Signal Assignments....... 7-15

7-5 ESDI Data Pin/Signal Assignments................ 7-17

7-6 Sample User Panel

...............

7-18

7-7 Write-Protect Input Signal

.....................

7-19

7-8 Pin Locations for Power Connector

........

7-20

vi Table of Contents

PREFACE

This reference manual explains how to install, test, and operate the

MD21 Disk Controller. It provides you with the following information:

• Installation instructions

• Disk Controller Specifications

• Compatibility information

• Drive Configuration Parameters

• Initialization and Self-Test Procedures

• Interface information

• A guide to troubleshooting

• PROM Removal and Replacement

This manual has been designed to be used with the Emulex SCSI Disk

Controller Programming Reference Manual (manual number MD2352501) and

it assumes familiarity with the SCSI standard and the ESDI disk drive

interface specification.

The Small Computer System Interface (SCSI) command set for the MD21

Controller is based on the ANSI X3.131-1986 SCSI Specification.

Copies of the ANSI SCSI Specification can be obtained from the

following publisher:

American National Standard for Information Systems - Small

Computer System Interface (SCSI), ANSI X3.131 - 1986

Computer and Business Equipment Manufacturers Association

311 First Street, NW Suite 500

Washington, DC 20001

The ESDI interface standard for 5.25-inch Winchester disk drives is

described in the Enhanced Small Device Interface specification,

preliminary working document, ANSI X3T9.3/87 -** Revision 1.1 or

ESDI Revision F.3A, (26 January 1987). This specification is

available from:

Dal Allan

Vice Chairman X3T9.3

ENDL Consulting

14426 Black Walnut Court

Saratoga, CA 95070

(408) 867-6630

Table of Contents vii

EMULEX PRODUCT WARRANTY

CONTROLLER WARRANTY: Emulex warrants for a period of twelve (12)

months from the date of shipment that each Emulex controller product

supplied shall be free from defects in material and workmanship.

CABLE WARRANTY: All Emulex-provided cables are warranted for ninety

(90) days from the time of shipment.

The above warranties shall not apply to expendable components such as

fuses, bulbs, and the like, nor to connectors, adapters, and other

items not a part of the basic product. Emulex shall have no

obligation to make repairs or to cause replacement required through

normal wear and tear or necessitated in whole or in part by

catastrophe, fault or negligence of the user, improper or

unauthorized use of the product, or use of the product in such a

manner for which it was not designed, or by causes external to the

product, such as but not limited to, power failure or air

conditioning. Emulex's sole obligation hereunder shall be to repair

or replace any defective product, and, unless otherwise stated, pay

return transportation cost for such replacement.

Purchaser shall provide labor for removal of the defective product,

shipping charges for return to Emulex, and installation of its

replacement. THE EXPRESSED WARRANTIES SET FORTH IN THIS AGREEMENT

ARE IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING,

WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR

A PARTICULAR PURPOSE, AND ALL OTHER WARRANTIES ARE HEREBY DISCLAIMED

AND EXCLUDED BY EMULEX. THE STATED EXPRESS WARRANTIES ARE IN LIEU OF

ALL OBLIGATIONS OR LIABILITIES ON THE PART OF EMULEX FOR DAMAGES,

INCLUDING BUT NOT LIMITED TO SPECIAL, INDIRECT, OR CONSEQUENTIAL

DAMAGES ARISING OUT OF, OR IN CONNECTION WITH THE USE OR PERFORMANCE

OF THE PRODUCT.

RETURNED MATERIAL: Warranty claims must be received by Emulex within

the applicable warranty period. A replaced product, or part thereof,

shall become the property of Emulex and shall be returned to Emulex

at Purchaser's expense. All returned material must be accompanied by

a RETURN MATERIALS AUTHORIZATION (RMA) number assigned by Emulex.

viii Warranty

Section 1

INTRODUCTION

1.1 OVERVIEW

The MD21/S2 Disk Controller is a single-board controller designed

to interconnect Small Computer System Interface (SCSI) host

adapters and controllers to one or two Enhanced Small Device

Interface (ESDI) ,5.25-inch Winchester disk drives. The controller

features the single-ended SCSI option for drivers and receivers.

For brevity, the reference MD21 will be used throughout this

manual.

In combination with an independent host adapter, the SCSI bus

allows a wide variety of computers to interface with the MD21

Controllers. Compatible computers include IBM Personal Computer

systems such as the IBM PC-XT, Q-Bus, VMS Bus, VAX UNIX, and

Multibus-based computers. Up to eight bus devices, in any

combination of host systems and intelligent controllers, can be

supported by the SCSI bus. The MD21 Controller, in combination

with one or two ESDI 5.25-inch magnetic disk drives, provides a

low-cost, compact storage subsystem.

The MD21 Controller's architecture and SCSI features it supports

make it an ideal building block for use by OEMs and system

integrators. The MD21 Controller supports a powerful set of SCSI

commands. By using those commands, an efficient multiple-initiator

configuration can be constructed with the support of the disconnect

function. (The disconnect function allows the MD21 Controller,

when it is performing a time-consuming task, to release the SCSI

bus temporarily and reconnect at a later time when the task is

complete.) The MD21 Controller supports all required SCSI commands

and the SCSI Common Command Set (CCS) for direct-access devices

described in the CCS standard.

Emulex currently offers other SCSI bus microcontrollers that can be

used with SCSI bus subsystems. These include the MT02/MT03 and the

MD01. The MT02/MT03 Tape Controller interfaces the SCSI bus to a

5.25-inch streaming cartridge tape drive. The MD01 Disk Controller

connects one or two ST506 interface 5.25-inch disk drives to the

SCSI bus. Also, the MD23/24 Disk Controller interfaces the SCSI bus

to up to four ESDI single-ended/differential drives and the MD32

connects up to four SMD/SMD-E drives to the SCSI bus.

In addition to basic stand-alone controller products, Emulex also

offers complete SCSI bus disk and tape packaged subsystems for

microcomputer applications.

Introduction 1-1

Overview

1.2 FEATURES

The MD21 Controller features are summarized below. More details on

these features are given in subsequent sections.

• Industry standard 5.25-inch form factor and mounting

• Operates from single +5 volt source

• 32K byte by 9-bit on-board dynamic RAM

• 8031 microprocessor operating at 12.0 mHz

• Power Fail Detect input

• User Panel Interface which supports:

-- Write protect switches

— Write protect indicators

— Ready indicators

• Write protect from the drive

• Support of one or two ESDI Disk Drives

• Provides a transfer rate up to fifteen megabits/sec at the

ESDI interface

• Supports physical sector sizes of 256 and 512 bytes

• Supports hard or soft sectoring

• Provides defect skipping, using slip sectoring

• Sequenced drive start up

• Supports embedded servo drives

• Auto configuration during power-up

• Defect management including manufacturer's defect list

• Overlapped Seeks

• Will not destroy manufacturer's defect list

• Provides transfer rate of up to 1.25 Mbytes/sec at the SCSI

interface

1-2 Introduction

• Conforms to the latest ANSI Specification (listed on page

vii)

• Supports the SCSI Direct Access Device Common Command Set

• Supports SCSI disconnect/reconnect option

• Diagnostic Commands support physical addressing

• Track-to-track and cylinder-to-cylinder format skewing

• Command queuing for each LUN

• Supports logical block sizes of 256, 512, 1024, 2048, and

4096 bytes

• 48-bit ECC correcting up to 17 bits in error

• Supports SCSI bus parity

• ESDI pass-through commands and status

1.3 ORGANIZATION OF THE MANUAL

This manual is designed to help you integrate the MD21 Controller

hardware into a subsystem. It provides technical information about

the controller and brief overviews of the SCSI and ESDI interfaces.

The manual provides no information about the SCSI command set or

protocol. For this information, please refer to the Emulex SCSI

Disk Controller Programming Reference Manual (manual number

MD2352501).

The contents of the seven sections and two appendices of the MD21

Disk Controller manual are briefly described below.

Section 1 Introduction: This section briefly describes the MD21

Controller, provides a list of its features, and

describes the organization of this manual. (This

section.)

Section 2 General Description: This section contains overviews of

the MD21 Controller, the SCSI bus, and the ESDI

interface. It also discusses SCSI and ESDI

compatibility.

Section 3 MD21 Controller Specifications: This section contains

specifications for the major components of the MD21

Controller .

Section 4

Drive Configuration Parameters: This section contains

recommended parameters of the ESDI disk drives.

Introduction 1-3

Overview

Section 5

Section 6

Section 7

Appendix i

Appendix ]

Installation: This section contains the information

necessary to set up and install the MD21 Controller in

your system.

Controller Initialization and Self-Test Procedures

This section describes the diagnostic features of the

MD21 Controller, including power up and reset tests and

• online host-initiated diagnostics.

Interfaces: This section describes the SCSI bus and ESDI

disk drive interfaces. It also describes the user panel

and DC power connections.

V Troubleshooting: This appendix provides information

regarding technical support and service.

5 PROM Removal and Replacement: This appendix contains

instructions to remove and replace the firmware so that

you can upgrade the MD21 Disk Controller in the field.

1-4 Introduction

Section 2

GENERAL DESCRIPTION

2.1 INTRODUCTION

This section provides brief overviews of the major components of

the MD21 Disk Controller subsystem. For more specific information

about the SCSI Bus Interface and about the ESDI Interface, please

refer to the ANSI SCSI Specification and the Enhanced Small Device

Interface Specification listed on page vii.

For reference convenience, Section 2 is divided into five

subsections, as listed in the following table:

Subsection Title

2.1

Introduction

2.2

Disk Controller Overview

2.3 SCSI Bus Overview

2.4

ESDI Overview

2.5 Compatibility

2.2 MD21 DISK CONTROLLER OVERVIEW

2.2.1 PHYSICAL DESCRIPTION

The MD21 Controller, shown in Figure 2-1, is assembled on a single

board approximately 14.6 centimeters by 20.3 centimeters (5.25

inches by 7.75 inches). It can be installed directly on a mounting

bracket located in the subsystem that contains an ESDI 5.25-inch

Winchester disk drive. The MD21 Controller contains the following

major components:

• Two Emulex custom Very Large Scale Integrated (VLSI) chips:

a Buffer Controller and a disk formatter.

• An 8031 microprocessor chip

• A 32-kilobyte (K byte) Erasable Programmable Read Only

Memory (EPROM), and a 32K byte Random Access Memory (RAM)

for data buffering.

Figure 2-1 shows the MD21 Disk Controller and its components.

General Description 2-1

MD21 Disk Controller Overview

MD2103-0785

Figure 2-1. The MD21 Disk Controller

2-2 General Description

MD21 Disk Controller Overview

2.2.2 FUNCTIONAL OVERVIEW

Figure 2-2 is a block diagram that shows the major functional

elements of the MD21. The MD21 is organized around the 8031

microprocessor, the SCSI protocol controller, the disk formatter,

and the buffer controller. The disk formatter and the buffer

controller are custom VLSI chips designed by Emulex.

Two buses are used in the MD21: the data bus and the microprocessor

bus.

The data bus is connected directly to the disk formatter, SCSI

protocol controller, buffer memory, and buffer controller. The

buffer controller is connected directly to the data bus and the

microprocessor bus, providing an interface between them.

Therefore, the buffer controller provides a data path between the

buffer memory, the 8031 microprocessor, disk formatter, and SCSI

protocol controller.

The microprocessor bus provides a path for transmission of control

and status information between the 8031 microprocessor, EPROM,

buffer controller, and disk interface. This bus is completely

separate from the data bus. The microprocessor may access the data

bus via the buffer controller interface.

The MD21 SCSI Interface is implemented using a single LSI chip on

the MD21 Controller. In response to commands from the initiator,

the chip establishes and monitors SCSI bus phases appropriate to

the command. It performs SCSI signal control and timing functions.

General Description 2-3

MD21 Disk Controller Overview

MD2103-0781

Figure 2-2. MD21 Controller Block Diagram

2-4 General Description

MD21 Disk Controller Overview

2.2.,2.1 8031 Microprocessor

With the disk formatter, the 8031 microprocessor controls all disk

drive operations. These disk operations include drive control, head

positioning, and reading drive status.

During disk operations, the disk formatter controls formatting of

the data that is written to, and read from, the disk drive. The

8031 microprocessor generates read and write commands that are

executed by the disk formatter. All read and write commands

involve operations only on a single data block (256 or 512 bytes).

2.2.2.2 Disk Formatter

The disk formatter is a 40-pin VLSI IC fabricated with CMOS gate

array technology. This circuit, along with the 8031

microprocessor, handles the read and write operations of the disk

drives.

2.2.2.3 Buffer Controller

The buffer controller is a 68-pin VLSI IC fabricated with CMOS

gate-array technology. The circuit is basically a three-channel

DMA controller. The buffer controller controls data movement in or

out of a dynamic buffer memory and provides the connection between

the microprocessor bus and the data bus.

The buffer controller circuit provides the address and control for

multiple MD21 Controller activities that access a dynamic buffer

memory. The buffer controller performs the following operations:

• Handles buffer addressing and control operations for the

disk formatter

• Handles buffer addressing and control operations for the

SCSI protocol controller

• Handles dynamic memory timing and refresh

• Performs parity checking and generation for the buffer

memory

• Connects the microprocessor bus to the data bus

• Decodes the microprocessor address for the buffer memory and

the internal input/output (I/O) space in the MD21 Controller

• Determines priority of buffer memory access

General Description 2-5

SCSI Bus Overview

2.3 SCSI BDS OVERVIEW

The Small Computer System Interface (SCSI)* is a standard interface

established to support mass storage, printer output, and network

communication for microcomputers and minicomputers. The interface

is an eight-port, daisy-chained bus. The SCSI command standard for

the MD21 Controller is based on the ANSI SCSI Interface

Specification listed on page vii.

The SCSI bus can support up to eight SCSI host adapters and/or

controllers. Each controller can be connected to a maximum of

eight devices (called Logical Unit Numbers, or LUNs). The MD21

Controller hardware supports any combination of host adapters,

intelligent controllers, or intelligent peripherals connected to

the SCSI bus. The MD21 Controller supports one or two LUNs (ESDI

disk drives). Three basic SCSI configurations are supported with

the MD21 Controller and SCSI bus:

• Single initiator, single target

• Single initiator, multi target

• Multi initiator, multi target

Communication on the SCSI bus occurs between a host adapter and a

controller. When a host adapter and a controller communicate, one

acts as the Initiator and the other acts as the Target. The

Initiator (usually the host adapter) originates an operation, and

the Target (usually a peripheral controller, such as the MD21

Controller) performs the operation. Sample system configurations

supported by MD21 Controller hardware are shown in Figure 2-3.

Some SCSI bus functions are assigned to the Initiator and some

functions are assigned to the Target. The Initiator can arbitrate

for control of the SCSI bus and select a specific Target. The

Target can request the transfer of command, data, status, or other

information via the SCSI bus. In some circumstances, the Target

can arbitrate for control of the SCSI bus to reselect an Initiator

and continue an operation. Sometimes, the Target becomes an

Initiator and arbitrates for control of the SCSI bus.

SCSI bus data transfer operations are asynchronous and follow a

defined request/acknowledge (REQ/ACK) handshake protocol. (This

protocol is defined in the ANSI SCSI specification.) One eight-bit

byte of information can be transferred with each handshake.

The SCSI bus consists of 18 signal lines. Nine signal lines are

for an eight-bit data bus with parity; the other nine signal lines

are for control and status signals that coordinate data transfer

operations between the host adapter and SCSI controllers. SCSI bus

signals are described in more detail in subsection 7.2.3.1.

2-6 General Description

SCSI Bus Overview

PERIPHERAL UNITS SUCH AS RIGID DISKS

SINGLE INITIATOR, SINGLE TARGET

MULTI INITIATOR, MULTI TARGET

MD2103-0582

Figure 2-3

Sample SCSI Bus Configuration

General Description 2-7

ESDI Overview

2.4 ESDI OVERVIEW

The Enhanced Small Device Interface (ESDI) is a standard interface

established to support multiple disk drives on the same controller.

ESDI was designed to extend the capabilities of the ST506

interface. The following points regarding the MD21 implementation

of the ESDI should be noted:

• The data separator is on the drive (instead of the

controller as in ST506 interfaces)? therefore, NRZ data can

be used between controller and drive.

• The drive, not the controller, provides the reference clock.

• On the data cable, ESDI replicates rotational information

from the control cable so that each drive position can be

monitored radially. This capability increases performance in

multiple-disk configurations.

• ESDI supports higher data transfer rates.

A typical multi-drive ESDI configuration is shown in Figure 2-4.

M D 2 1 0 3 -0 9 9 0

Figure 2-4. Typical Multi-Drive Configuration

2-8 General Description

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