CONTENTS

  Title Page

  Copyright Page

  Preface

  1      Physical Characteristics

  1.1     Physical Description

  1.2     Cable Requirements
    1.2.1      Single-Ended Cable
    1.2.2      Ordering Information for Digital Cables

  1.3     Connector Requirements
    1.3.1      50-Pin Nonshielded Device and Cable Connector
    1.3.2      50-Pin Shielded Device and Cable Connector
    1.3.3      50-Pin Connector Pin Assignments
    1.3.4      68-Pin Connector
    1.3.5      68-Pin Connector Pin Assignments

  1.4     Electrical Description
    1.4.1      Single-Ended Signals
    1.4.2      Terminator Power
    1.4.3      Signal Termination
    1.4.4      Reserved Lines

  1.5     SCSI Bus

  1.6     SCSI Bus Signals
    1.6.1      Signal Values
    1.6.2      Signal Sources

  1.7     SCSI Bus Timing

  2      Logical Characteristics

  2.1     SCSI Bus Phases
    2.1.1      Bus Free Phase
    2.1.2      Arbitration Phase
    2.1.3      Selection Phase
    2.1.4      Reselection Phase
    2.1.5      Information Transfer Phases
    2.1.6      Command Phase
    2.1.7      Data Phase
    2.1.8      Status Phase
    2.1.9      Message Phase
    2.1.10     Signal Restrictions Between Phases

  2.2     SCSI Bus Conditions
    2.2.1      Attention Condition
    2.2.2      Reset Condition

  2.3     SCSI Bus Phase Sequences

  2.4     SCSI Pointers

  2.5     SCSI Message System
    2.5.1      Messages-Format and Codes
    2.5.2      Messages-Implemented by the VMS Operating System

  2.6     Messages
    2.6.1      ABORT
    2.6.2      COMMAND COMPLETE
    2.6.3      DISCONNECT
    2.6.4      RESTORE POINTERS
    2.6.5      SAVE DATA POINTER

  3      SCSI Commands and Status

  3.1     Command Implementation Requirements
    3.1.1      Reserved
    3.1.2      Operation Code Types

  3.2     Command Descriptor Block
    3.2.1      Operation Code
    3.2.2      Logical Unit Number
    3.2.3      Logical Block Address
    3.2.4      Transfer Length
    3.2.5      Parameter List Length
    3.2.6      Allocation Length
    3.2.7      Control Byte

  3.3     Status

  3.4     Command Processing Considerations and Exception Conditions
    3.4.1      Programmable Operating Definition
    3.4.2      Incorrect Initiator Connection
    3.4.3      Selection of an Invalid Logical Unit
    3.4.4      Parameter Rounding

  3.5     Asynchronous Event Notification

  3.6     Contingent Allegiance Condition

  3.7     Extended Contingent Allegiance Condition

  3.8     Unit Attention Condition

  4      Characteristics of Most Device Types

  4.1     Model for Most Device Types
    4.1.1      SCSI Addresses
    4.1.2      Commands Implemented by SCSI Targets

  4.2     Commands for Most Device Types

  5      Power-On Protocols and Initialization Procedures

  5.1     Dynamic Reconfiguration of Devices

  5.2     External Boxes

  5.3     Device Behavior Following Power-On

  5.4     Device Behavior Following Bus Reset

  A   Associated Documents

  B   ANSI SCSI-2 Specification Cross-Reference

  Glossary
    ANSI . . . Common Command Set (CCS)
    command descriptor block (CDB) . . . ESD
    host adapter . . . LUN
    MSB . . . priority
    processor . . . SCSI port
    signal release . . . zero

  FIGURES

  1-1        Digital SCSI Connector Cables

  1-2        50-Pin Nonshielded SCSI Device Connector

  1-3        50-Pin Nonshielded SCSI Cable Connector

  1-4        50-Pin Shielded SCSI Device Connector

  1-5        50-Pin Shielded SCSI Cable Connector

  1-6        Nonshielded Pin Assignments

  1-7        Shielded Pin Assignments

  1-8        68-Pin Connector Assembly

  1-9        Configuration/Dimensions for 68-Pin Connector

  1-10       Cover and Strain Relief for 68-Pin Connector

  1-11       68-Pin Connector Pin Assignments

  1-12       Termination

  1-13       SCSI ID Bits

  1-14       Sample SCSI Configurations

  1-15       Signal Sources

  2-1        Information Transfer Phases

  2-2        SCSI Bus Phase Sequences

  2-3        Sequence of Signals in an INQUIRY Command

  2-4        SCSI Pointers

  2-5        Message Codes

  3-1        CDB for Six-Byte Commands

  3-2        CDB for Ten-Byte Commands

  3-3        Operation Code

  3-4        Control Byte

  3-5        Status Byte

  TABLES

  1 Digital's Implementation of SCSI

  1-1        Cable Ordering Information

  1-2        Terminator Ordering Information

  1-3        SCSI ID Assignments

  1-4        SCSI Bus Signals

  1-5        SCSI Bus Timing Values

  2-1        SCSI Bus Phases

  2-2        Digital Systems and Associated Host Adapter

  2-3        Mnemonics Used in Figure 2-5

  2-4        Extended Message Format

  2-5        Extended Message Codes

  2-6        SCSI Messages

  3-1        Operation Code Types

  3-2        Status Byte Codes

  4-1        Commands for Most Device Types

  B-1        Cross-Reference to ANSI SCSI-2 Specification