Universal Serial Bus
Specification
Compaq
Intel
Microsoft
NEC
Revision 1.1
September 23, 1998
Universal Serial Bus Specification Revision 1.1
ii
Scope of this Revision
The 1.1 revision of the specification is intended for product design. Every attempt has been made to ensure a
consistent and implementable specification. Implementations should ensure compliance with this revision.
Revision History
Revision Issue Date Comments
0.7 November 11, 1994 Supersedes 0.6e.
0.8 December 30, 1994 Revisions to Chapters 3-8, 10, and 11. Added
appendixes.
0.9 April 13, 1995 Revisions to all the chapters.
0.99 August 25, 1995 Revisions to all the chapters.
1.0 FDR November 13, 1995 Revisions to Chapters 1, 2, 5-11.
1.0 January 15, 1996 Edits to Chapters 5, 6, 7, 8, 9, 10, and 11 for
consistency.
1.1 September 23, 1998 Updates to all chapters to fix problems identified.
Universal Serial Bus Specification
Copyright © 1998, Compaq Computer Corporation,
Intel Corporation, Microsoft Corporation, NEC Corporation.
All rights reserved.
INTELLECTUAL PROPERTY DISCLAIMER
THIS SPECIFICATION IS PROVIDED “AS IS” WITH NO WARRANTIES WHATSOEVER INCLUDING
ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY
WARRANTY OTHERWISE ARISING OUT OF ANY PROPOSAL, SPECIFICATION, OR SAMPLE.
A LICENSE IS HEREBY GRANTED TO REPRODUCE AND DISTRIBUTE THIS SPECIFICATION FOR
INTERNAL USE ONLY. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR
OTHERWISE, TO ANY OTHER INTELLECTUAL PROPERTY RIGHTS IS GRANTED OR INTENDED
HEREBY.
AUTHORS OF THIS SPECIFICATION DISCLAIM ALL LIABILITY, INCLUDING LIABILITY FOR
INFRINGEMENT OF PROPRIETARY RIGHTS, RELATING TO IMPLEMENTATION OF
INFORMATION IN THIS SPECIFICATION. AUTHORS OF THIS SPECIFICATION ALSO DO NOT
WARRANT OR REPRESENT THAT SUCH IMPLEMENTATION(S) WILL NOT INFRINGE SUCH
RIGHTS.
GeoPort and Apple Desktop Bus are trademarks of Apple Computer, Inc.
Windows and Windows NT are trademarks and Microsoft and Win32 are registered trademarks of Microsoft Corporation.
IBM, PS/2, and Micro Channel are registered trademarks of International Business Machines Corporation.
AT&T is a registered trademark of American Telephone and Telegraph Company.
Compaq is a registered trademark of Compaq Computer Corporation.
UNIX is a registered trademark of UNIX System Laboratories.
I
2
C is a trademark of Phillips Semiconductors.
DEC is a trademark of Digital Equipment Corporation.
All other product names are trademarks, registered trademarks, or servicemarks of their respective owners.
Please send comments via electronic mail to techsup@usb.org
For industry information, refer to the USB Implementers Forum web page at http://www.usb.org
Universal Serial Bus Specification Revision 1.1
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Contents
CHAPTER 1 INTRODUCTION .................................................................................1
1.1 Motivation...............................................................................................................................................1
1.2 Objective of the Specification................................................................................................................1
1.3 Scope of the Document...........................................................................................................................2
1.4 Document Organization.........................................................................................................................2
CHAPTER 2 TERMS AND ABBREVIATIONS..........................................................3
CHAPTER 3 BACKGROUND..................................................................................11
3.1 Goals for the Universal Serial Bus......................................................................................................11
3.2 Taxonomy of Application Space..........................................................................................................12
3.3 Feature L
i
st...........................................................................................................................................12
CHAPTER 4 ARCHITECTURAL OVERVIEW........................................................15
4.1 USB System Description ......................................................................................................................15
4.1.1 Bus Topology..................................................................................................................................16
4.2 Physical Interface .................................................................................................................................17
4.2.1 Electrical .........................................................................................................................................17
4.2.2 Mechanical......................................................................................................................................17
4.3 Power.....................................................................................................................................................18
4.3.1 Power Distribution ..........................................................................................................................18
4.3.2 Power Management.........................................................................................................................18
4.4 Bus Protocol..........................................................................................................................................18
4.5 Robustness.............................................................................................................................................19
4.5.1 Error Detection................................................................................................................................19
4.5.2 Error Handling.................................................................................................................................19
4.6 System Configuration...........................................................................................................................19
4.6.1 Attachment of USB Devices ...........................................................................................................19
4.6.2 Removal of USB Devices................................................................................................................20
4.6.3 Bus Enumeration.............................................................................................................................20
4.7 Data Flow Types...................................................................................................................................20
4.7.1 Control Transfers.............................................................................................................................20
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4.7.2 Bulk Transfers.................................................................................................................................20
4.7.3 Interrupt Transfers...........................................................................................................................21
4.7.4 Isochronous Transfers.....................................................................................................................21
4.7.5 Allocating USB Bandwidth.............................................................................................................21
4.8 USB Devices..........................................................................................................................................21
4.8.1 Device Characterizations.................................................................................................................21
4.8.2 Device Descriptions ........................................................................................................................22
4.9 USB Host: Hardware and Software...................................................................................................24
4.10 Architectural Extensions .....................................................................................................................24
CHAPTER 5 USB DATA FLOW MODEL................................................................ 25
5.1 Implementer Viewpoints......................................................................................................................25
5.2 Bus Topology ........................................................................................................................................27
5.2.1 USB Host ........................................................................................................................................27
5.2.2 USB Devices...................................................................................................................................28
5.2.3 Physical Bus Topology....................................................................................................................29
5.2.4 Logical Bus Topology.....................................................................................................................30
5.2.5 Client Software-to-function Relationship........................................................................................30
5.3 USB Communication Flow ..................................................................................................................31
5.3.1 Device Endpoints ............................................................................................................................32
5.3.2 Pipes................................................................................................................................................33
5.4 Transfer Types......................................................................................................................................35
5.5 Control Transfers.................................................................................................................................36
5.5.1 Control Transfer Data Format.........................................................................................................36
5.5.2 Control Transfer Direction..............................................................................................................37
5.5.3 Control Transfer Packet Size Constraints........................................................................................37
5.5.4 Control Transfer Bus Access Constraints........................................................................................38
5.5.5 Control Transfer Data Sequences....................................................................................................40
5.6 Isochronous Transfers .........................................................................................................................41
5.6.1 Isochronous Transfer Data Format..................................................................................................41
5.6.2 Isochronous Transfer Direction.......................................................................................................41
5.6.3 Isochronous Transfer Packet Size Constraints ................................................................................41
5.6.4 Isochronous Transfer Bus Access Constraints ................................................................................42
5.6.5 Isochronous Transfer Data Sequences.............................................................................................43
5.7 Interrupt Transfers..............................................................................................................................43
5.7.1 Interrupt Transfer Data Format .......................................................................................................43
5.7.2 Interrupt Transfer Direction ............................................................................................................43
5.7.3 Interrupt Transfer Packet Size Constraints......................................................................................43
5.7.4 Interrupt Transfer Bus Access Constraints......................................................................................44
5.7.5 Interrupt Transfer Data Sequences..................................................................................................46
5.8 Bulk Transfers......................................................................................................................................46
5.8.1 Bulk Transfer Data Format .............................................................................................................47
5.8.2 Bulk Transfer Direction ..................................................................................................................47
5.8.3 Bulk Transfer Packet Size Constraints............................................................................................47
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5.8.4 Bulk Transfer Bus Access Constraints............................................................................................47
5.8.5 Bulk Transfer Data Sequences ........................................................................................................48
5.9 Bus Access for Transfers......................................................................................................................49
5.9.1 Transfer Management......................................................................................................................49
5.9.2 Transaction Tracking.......................................................................................................................52
5.9.3 Calculating Bus Transaction Times.................................................................................................54
5.9.4 Calculating Buffer Sizes in Functions and Software.......................................................................55
5.9.5 Bus Bandwidth Reclamation...........................................................................................................55
5.10 Special Considerations for Isochronous Transfers............................................................................55
5.10.1 Example Non-USB Isochronous Application..................................................................................56
5.10.2 USB Clock Model...........................................................................................................................59
5.10.3 Clock Synchronization ....................................................................................................................61
5.10.4 Isochronous Devices........................................................................................................................61
5.10.5 Data Prebuffering............................................................................................................................69
5.10.6 SOF Tracking..................................................................................................................................70
5.10.7 Error Handling.................................................................................................................................70
5.10.8 Buffering for Rate Matching ...........................................................................................................71
CHAPTER 6 MECHANICAL....................................................................................73
6.1 Architectural Overview........................................................................................................................73
6.2 Keyed Connector Protocol...................................................................................................................73
6.3 Cable......................................................................................................................................................74
6.4 Cable Assembly.....................................................................................................................................74
6.4.1 Detachable Cable Assemblies .........................................................................................................74
6.4.2 Full-speed Captive Cable Assemblies.............................................................................................76
6.4.3 Low-speed Captive Cable Assemblies ............................................................................................78
6.4.4 Prohibited Cable Assemblies...........................................................................................................80
6.5 Connector Mechanical Configuration and Material Requirements ................................................80
6.5.1 USB Icon Location..........................................................................................................................81
6.5.2 USB Connector Termination Data ..................................................................................................82
6.5.3 Series “A” and Series “B” Receptacles...........................................................................................82
6.5.4 Series “A” and Series “B” Plugs .....................................................................................................86
6.6 Cable Mechanical Configuration and Material Requirements ........................................................90
6.6.1 Description......................................................................................................................................90
6.6.2 Construction....................................................................................................................................91
6.6.3 Electrical Characteristics.................................................................................................................93
6.6.4 Cable Environmental Characteristics ..............................................................................................93
6.6.5 Listing .............................................................................................................................................94
6.7 Electrical, Mechanical and Environmental Compliance
Standards ................................................94
6.7.1 Applicable Documents..................................................................................................................102
6.8 USB Grounding ..................................................................................................................................102
6.9 PCB Reference Drawings...................................................................................................................102
