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On-The-Go Supplement to the
USB 2.0 Specification
Revision 1.0a
June 24, 2003
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
June 24, 2003
Revision History
Revision
Issue Date
Comment
0.7
11/07/2000
Revisions to all sections
0.8
04/06/2001
Revisions to all sections
0.9
09/05/2001
Revisions to all sections
1.0_rc1
10/15/2001
Minor edits to most sections
Defined TB_FS_BDIS for high speed HNP.
1.0
12/18/01
Minor edits to several sections
Defined RA_PLUG_ID and RB_PLUG_ID
1.0aRC1
11/19/2002
Updates reflected in Errata release 1
1.0aRC2
January 23, 2003
1.0aRC3
March 25, 2003
Clarify short versus long debounce and minor edits
1.0aRC4
March 28, 2003
Add figures clarifying long and short debounce and minor edits
1.0aRC5
April 30, 2003
Clarifying changes following review at April 23 face-to-face
1.0aRC6
June 13, 2003
Set copyright information
1.0a
June 24, 2003
Update contributor list, correct minor editorial errors in section 6
Add definition of “OTG Device”
Universal Serial Bus Specification Supplement
Copyright © 2001, 2003 USB Implementers Forum, Inc. (USB-IF).
All rights reserved.
INTELLECTUAL PROPERTY DISCLAIMER
THIS SPECIFICATION IS PROVIDED TO YOU “AS IS” WITH NO WARRANTIES WHATSOEVER,
INCLUDING ANY WARRANTY OF MERCHANTABILITY, NON-INFRINGEMENT, OR FITNESS FOR
ANY PARTICULAR PURPOSE. THE AUTHORS OF THIS SPECIFICATION DISCLAIM ALL
LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY PROPRIETARY RIGHTS,
RELATING TO USE OR IMPLEMENTATION OF INFORMATION IN THIS SPECIFICATION. THE
PROVISION OF THIS SPECIFICATION TO YOU DOES NOT PROVIDE YOU WITH ANY LICENSE,
EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY
RIGHTS.
All product names are trademarks, registered trademarks, or servicemarks of their respective owners.
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Contributors
Glen Chandler, Advanced-Connectek (Acon)
Chris Kolb, ARC International
Maria Pohlman, Aten
Ray Asbury, Cypress Semiconductor
Dave Cobbs, Cypress Semiconductor
Kosta Koeman, Cypress Semiconductor
David Wright, Cypress Semiconductor
Israel Zilberman, Cypress Semiconductor
Morten Christiansen, Ericsson
Ed Beeman, Hewlett-Packard
Matt Nieberger, Hewlett-Packard
Trung Le, Imation
Eric Huang, InSilicon
Dan Froelich, Intel Corp
Venkat Iyer, Intel Corp
Richard Lawrence, Intel Corp
Jeff Miller, Intel Corp
Francesco Liburdi, Lumberg
Ryan Hashimoto, Maxim
Paul E. Berg, MCCI
Terry Moore, MCCI
Rob Douglas, Mentor Graphics
Ian Parr, Mentor Graphics
Mark Hanson, Microsoft
Akira Aso, Molex
Mark Carlson, Motorola
Eric Overtoom, Motorola
Kazumasa Saito, NEC Systems
Esa Harma, Nokia
Mark Jenkins, Nokia
James Scales, Nokia
Sree Iyer, OnSpec
Peter Yi, Opti
Bill Stanley, Palm
Geert Knapen, Philips
Eric Lu, Philips
Chris Schell, Philips (Co-Chair)
Rik Stopel, Philips
Kenneth Tan, Philips
Jerome Tjia, Philips
David Wang, Philips
Hilbert Zhang, Philips
Keith Gallardo, Qualcomm
Terry Remple, Qualcomm (Co-Chair)
Joe Meza, SoftConnex
Dan Harmon, Texas Instruments
Jeff Kacines, Texas Instruments
Clarence Lewis, Texas Instruments
Richard Nie, Texas Instruments
Sue Vining, Texas Instruments
Joon Kim, TransDimension
Dave Murray, TransDimension
Jing Wang, TransDimension
David Wooten, TransDimension
Zong Liang Wu, TransDimension
Charles Brill, Tyco Electronics
Mark Paxson, USB-IF
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Table of Contents
1. Introduction.............................................................................................................................................. 1
1.1 General............................................................................................................................................. 1
1.2 Objective of the Supplement ............................................................................................................ 1
1.3 Intended Audience ........................................................................................................................... 1
2. Acronyms and Terms.............................................................................................................................. 3
3. Significant Features ................................................................................................................................ 5
3.1 USB 2.0 Specification Compliance .................................................................................................. 5
3.2 Dual-role Device ............................................................................................................................... 5
3.3 Targeted Peripheral List ................................................................................................................... 5
3.4 No Silent Failures ............................................................................................................................. 5
3.5 Supplying Current on VBUS.............................................................................................................. 6
3.6 Session Request Protocol ................................................................................................................ 6
3.7 Host Negotiation Protocol................................................................................................................. 6
3.8 Connectors ....................................................................................................................................... 6
3.9 Compliant Cable Assemblies ........................................................................................................... 6
3.10 Plug Overmolds ................................................................................................................................ 7
3.11 Cable Adapters................................................................................................................................. 7
3.12 Hubs ................................................................................................................................................. 7
3.13 Mandated Functionality .................................................................................................................... 7
4. Mechanical ............................................................................................................................................... 9
4.1 Introduction....................................................................................................................................... 9
4.2 Mini-Connector Mating ..................................................................................................................... 9
4.3 Color Coding................................................................................................................................... 10
4.4 Device, Cable and Adapter Delays ................................................................................................ 10
4.5 Compliant Usage of Connectors and Cables ................................................................................. 11
4.5.1 Cables ............................................................................................................................... 11
4.5.2 Overmolds ......................................................................................................................... 12
4.5.3 Mechanical Interfaces ....................................................................................................... 12
4.5.4 Receptacle Reference Designs ........................................................................................ 12
4.5.5 Connector Keying.............................................................................................................. 12
4.5.6 Right Angle Plugs.............................................................................................................. 12
4.5.7 Adapters ............................................................................................................................ 12
4.6 Drawings......................................................................................................................................... 13
5. Electrical Requirements........................................................................................................................ 33
5.1 A-Device Electrical Requirements.................................................................................................. 33
5.1.1 VBUS Output Voltage and Current..................................................................................... 33
5.1.2 VBUS Input Impedance ...................................................................................................... 33
5.1.3 VBUS Rise and Fall Time................................................................................................... 34
5.1.4 VBUS Capacitance............................................................................................................. 34
5.1.5 VBUS Leakage Voltage...................................................................................................... 34
5.1.6 Data Line Pull-down Resistance ....................................................................................... 34
5.1.7 Data Line Pull-up Resistance............................................................................................ 35
5.1.8 Data Line Leakage Voltage............................................................................................... 35
5.1.9 Data Line Discharge Time ................................................................................................ 35
5.1.10 VBUS Input Current Without Battery.................................................................................. 36
5.2 B-Device Electrical Requirements.................................................................................................. 36
5.2.1 VBUS Average Input Current ............................................................................................. 36
5.2.2 VBUS Peak Input Current................................................................................................... 36
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5.3
5.4
5.5
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5.2.3 VBUS Capacitance............................................................................................................. 36
5.2.4 Data Line Pull-down Resistance ....................................................................................... 36
5.2.5 Data Line Pull-up Resistance............................................................................................ 37
5.2.6 Data Line Leakage Voltage............................................................................................... 37
5.2.7 VBUS Input Current Without Battery .................................................................................. 37
Session Request Protocol .............................................................................................................. 37
5.3.1 Introduction ....................................................................................................................... 37
5.3.2 Initial Conditions................................................................................................................ 37
5.3.3 Data-line Pulsing ............................................................................................................... 38
5.3.4 VBUS Pulsing...................................................................................................................... 39
5.3.5 B-Device VBUS Pulsing Current ........................................................................................ 39
5.3.6 A-Device Session Valid..................................................................................................... 39
5.3.7 B-Device Session Valid..................................................................................................... 39
5.3.8 Duration of SRP ................................................................................................................ 39
5.3.9 Order of Methods .............................................................................................................. 40
5.3.10 Response Time of A-device ............................................................................................. 40
5.3.11 Repetition of SRP ............................................................................................................. 40
Electrical Characteristics ................................................................................................................ 41
Device Timings ............................................................................................................................... 43
6. Host Negotiation Protocol .................................................................................................................... 50
6.1 Introduction..................................................................................................................................... 50
6.2 Description Priority ......................................................................................................................... 50
6.3 HNP Overview ................................................................................................................................ 50
6.4 OTG Descriptor .............................................................................................................................. 52
6.4.1 srp_support ....................................................................................................................... 52
6.4.2 hnp_support ...................................................................................................................... 52
6.5 Set Feature Commands ................................................................................................................. 52
6.5.1 b_hnp_enable ................................................................................................................... 53
6.5.2 a_hnp_support .................................................................................................................. 53
6.5.3 a_alt_hnp_support ............................................................................................................ 54
6.6 State Machine Parameters............................................................................................................. 54
6.6.1 Inputs................................................................................................................................. 54
6.6.2 Internal Variables .............................................................................................................. 58
6.6.3 Outputs.............................................................................................................................. 58
6.6.4 Informative Variables ........................................................................................................ 58
6.6.5 Timers ............................................................................................................................... 59
6.6.6 Test Device Support.......................................................................................................... 59
6.7 Timing Summary ............................................................................................................................ 60
6.7.1 B-device becoming Host ................................................................................................... 60
6.7.2 A-device becoming Peripheral .......................................................................................... 60
6.8 State Diagrams............................................................................................................................... 61
6.8.1 Dual-role A-Device ............................................................................................................ 62
6.8.2 Dual-Role B-Device........................................................................................................... 66
6.8.3 Peripheral-Only, B-Device ................................................................................................ 68
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Figures
Figure 4-1 Mini-A to Mini-B Cable................................................................................................................. 14
Figure 4-2 Standard-B to Mini-A Cable......................................................................................................... 15
Figure 4-3 Mini-A to Captive Cable............................................................................................................... 16
Figure 4-4 Mini-A Plug Overmold, Straight ................................................................................................... 17
Figure 4-5 Mini-B Plug Overmold, Straight ................................................................................................... 18
Figure 4-6 Mini-A Plug Interface - 1 of 2 ....................................................................................................... 19
Figure 4-7 Mini-A Plug Interface - 2 of 2 ....................................................................................................... 20
Figure 4-8 Mini-A Receptacle Interface ........................................................................................................ 21
Figure 4-9 Mini-AB Receptacle Interface...................................................................................................... 22
Figure 4-10 Mini-A Receptacle Reference Design ....................................................................................... 23
Figure 4-11 Mini-AB Receptacle Reference Design..................................................................................... 24
Figure 4-12 Mini-A Plug Blockage ................................................................................................................ 25
Figure 4-13 Mini-B Plug Blockage ................................................................................................................ 26
Figure 4-14 Mini-A Plug, Side Right Angle ................................................................................................... 27
Figure 4-15 Mini-A Plug, Down Right Angle ................................................................................................. 28
Figure 4-16 Mini-B Plug, Side Right Angle ................................................................................................... 29
Figure 4-17 Mini-B Plug, Down Right Angle ................................................................................................. 30
Figure 4-18 Adapter, Standard-A receptacle to Mini-A plug......................................................................... 31
Figure 4-19 Adapter, Mini-A receptacle to Standard-A plug......................................................................... 32
Figure 5-1 A-device Input Impedance (VBUS not driven) ............................................................................ 33
Figure 5-2 A-device SRP Timing Reference................................................................................................. 45
Figure 5-3 A-device HNP Timing Reference (FS) ........................................................................................ 45
Figure 5-4 A-device HNP Timing Reference (HS) ........................................................................................ 46
Figure 5-5 B-device SRP Timing Reference................................................................................................. 48
Figure 5-6 B-device HNP Timing Reference (FS) ........................................................................................ 48
Figure 5-7 B-device HNP Timing Reference (HS) ........................................................................................ 49
Figure 6-1 HNP Sequence of Events............................................................................................................ 51
Figure 6-2 Dual-Role A-device State Diagram ............................................................................................. 62
Figure 6-3 Dual-Role B-device State Diagram ............................................................................................. 66
Figure 6-4 SRP Capable Peripheral-Only B-device State Diagram ............................................................. 68
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Tables
Table 4-1.
Table 4-2.
Table 4-3.
Table 4-4.
Table 4-5.
Table 5-1.
Table 5-2.
Table 5-3.
Table 5-4.
Table 6-1.
Table 6-2.
Table 6-3.
Table 6-4.
vi
Plugs Accepted By Receptacles.................................................................................................... 9
Mini-A Plug Pin Assignments ...................................................................................................... 10
Color Coding for Plugs and Receptacles .................................................................................... 10
Maximum Delay for Mini-Connector and Cable........................................................................... 11
Maximum Delay for Standard Connector Cable.......................................................................... 11
DC Electrical Characteristics ....................................................................................................... 41
A-device Timing ........................................................................................................................... 43
B-device Timing ........................................................................................................................... 44
Device Timing Comparison ......................................................................................................... 47
OTG Descriptor............................................................................................................................ 52
Set Feature Command Format.................................................................................................... 53
On-The-Go Feature Selectors ..................................................................................................... 53
Dual-Role Device Timers............................................................................................................. 59
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
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1. Introduction
1.1
General
USB has become a popular interface for exchanging data between PC’s and peripherals. An increasing
number of portable peripherals are using the USB interface to communicate with the PC. Many of these
portable devices would benefit from being able to communicate to each other over the USB interface,
yet certain aspects of USB make this difficult to achieve.
Specifically, USB communication can only take place between a host and a peripheral. However, in
order to qualify as a PC host, a device must have several characteristics, including:
•
•
•
storage for a large number of device drivers,
the ability to source a large current, and
a Series “A” host connector receptacle.
It is not practical for many portable devices to have all of the above characteristics, and in many cases,
these characteristics are not needed in order to interface portable devices with each other.
In order to enable these limited-requirement, portable USB applications, this supplement to the USB 2.0
specification was developed that allows a portable device to take on the role of a limited USB host,
without the burden of supporting all the above functions of a PC.
1.2
Objective of the Supplement
The objective of this supplement is to define a minimal set of changes to the USB 2.0 specification, such
that portable USB applications are enabled.
This is not a stand-alone document. It is a supplement to the USB 2.0 specification. Any aspects of USB
that are not specifically changed by this supplement are governed by the USB 2.0 specification.
1.3
Intended Audience
This specification is targeted to developers of PC peripherals and portable consumer electronic devices.
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2. Acronyms and Terms
This chapter lists and defines terms and abbreviations used throughout this specification.
A-Device
A device with a Standard-A or Mini-A plug inserted into its receptacle. An
A-device supplies power to VBUS; is host at the start of a session; and
under certain conditions as described in Section 6, the A-device will
relinquish the role of host to a dual-role B-device.
Application
A generic term referring to any software that is running on a device that
can control the behavior or actions of the USB port(s) on a device.
B-Device
A device with a Standard-B or Mini-B plug inserted into its receptacle.
The B-device is a peripheral at the start of a session. If the device is
dual-role, it may be granted the role of host from the A-device (see
Section 6).
Dual-role device
A device that has the following features and characteristics:
•
•
•
•
•
•
•
•
•
limited Host capability
full-speed operation as peripheral (high-speed optional)
full-speed support as host (low-speed and high-speed
optional)
Targeted Peripheral List
Session Request Protocol
Host Negotiation Protocol
one, and only one, Mini-AB receptacle
minimum 8 mA output on VBUS
means for communicating messages to the user
FS
Full Speed
HS
High Speed
Host
A physical entity that is attached to a USB cable and is acting in the role
of the USB host as defined in the USB Specification, Revision 2.0. This
entity initiates all data transactions and provides periodic Start of Frames
(SOF’s).
HNP
Host Negotiation Protocol. (See Section 6.)
ID
Identification. Denotes the pin on the Mini connectors that is used to
differentiate a Mini-A plug (ID pin resistance to ground < 10Ω) from a
Mini-B plug (ID pin resistance to ground greater than 100 kΩ).
OTG
On-The-Go
OTG device
See Dual-role device
Peripheral
A physical entity that is attached to a USB cable and is currently
operating as a “device” as defined in the USB Specification, Revision 2.0.
The Peripheral responds to low level bus requests from the Host.
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SE0
Single Ended Zero
Session
The period of time that VBUS is above a device’s session valid threshold.
For an A-device, the session valid threshold is VA_SESS_VLD, while for a
B-device it is VB_SESS_VLD.
SOF
Start of Frame
SRP
Session Request Protocol
Targeted Peripheral
List
A list of USB peripherals that a particular dual-role device can support
when it is acting as a host.
USB
Universal Serial Bus
USB-IF
USB Implementers Forum
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
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3. Significant Features
This section identifies the significant features of the OTG supplement. The purpose of this section is not
to present all the technical details associated with each major feature, but rather to highlight its
existence. Where appropriate, this section references other parts of the document where further details
can be found.
3.1
USB 2.0 Specification Compliance
Any device with OTG features is first and foremost a USB peripheral that is compliant with the USB 2.0
specification.
3.2
Dual-role Device
In addition to being a fully compliant USB 2.0 peripheral, a dual-role device must include the following
features and characteristics:
•
•
•
•
•
•
•
•
•
3.3
a limited Host capability
full-speed operation as a peripheral (high-speed optional)
full-speed support as a host (low-speed and high-speed optional)
Targeted Peripheral List
Session Request Protocol
Host Negotiation Protocol
one, and only one, Mini-AB receptacle
minimum 8 mA output on VBUS
means for communicating messages to the user
Targeted Peripheral List
When acting as Host, a dual-role device is not required to support operation with all other types of USB
peripherals. It is up to the manufacturer of each dual-role device to determine what peripherals the dualrole device will support and provide a list of those peripherals. This is the called the dual-role device’s
“Targeted Peripheral List”.
In its most primitive form, the Targeted Peripheral List is simply a list of peripherals, where each
peripheral is identified by a manufacturer, the kind of the device, and a model number.
The Targeted Peripheral List may also contain defined OTG peripheral types, such as an “OTG
keyboard”, or an “OTG camera”, etc. In order to qualify as a member of one of these OTG peripheral
types, a peripheral would need to exhibit the electrical and software characteristics defined for that OTG
peripheral type.
3.4
No Silent Failures
Whenever the cabling allows USB devices to be connected, and the devices do not support the type of
communication being requested by the user, then the devices shall provide messages to the user that
allow him or her to understand the problem, and correct it if possible. Insofar as is possible, the
messages shall be self explanatory, and shall not require the user to reference a manual or other
additional material.
For example, if a B-device generates SRP, the A-device may try to give control to the B-device by trying
to enable HNP. The B-device may not be HNP capable. The A-device may determine that the B-device
is not HNP capable because the B-device is LS or because the B-device STALL’s the command that
enables HNP. When the A-device determines that the B-device is not HNP capable and that the Bdevice is not supported, the A-device is responsible for providing an informative message to the user
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that the B-device is not supported. If, however, the B-device is HNP capable it will have responsibility for
informing the user if the A-device is not supported.
3.5
Supplying Current on VBUS
A dual-role device must be able to source a minimum of 8 mA on VBUS when it is the A-device and a
session is in progress.
3.6
Session Request Protocol
The OTG supplement defines a Session Request Protocol (SRP), which allows a B-device to request
the A-device to turn on VBUS and start a session. This protocol allows the A-device, which may be
battery powered, to conserve power by turning VBUS off when there is no bus activity while still providing
a means for the B-device to initiate bus activity.
Any A-device, including a PC or laptop, is allowed to respond to SRP. Any B-device, including a
standard USB peripheral, is allowed to initiate SRP. A dual-role device is required to be able to initiate
and respond to SRP.
The details of this protocol are found in Section 5.3.
3.7
Host Negotiation Protocol
The Host Negotiation Protocol (HNP) allows the Host function to be transferred between two directly
connected dual-role devices and eliminates the need for a user to switch the cable connections in order
to allow a change in control of communications between the devices. HNP will typically be initiated in
response to input from the user or an Application on the dual-role B-device. HNP may only be
implemented through the Mini-AB receptacle on a device.
3.8
Connectors
The USB 2.0 specification defines the following connectors:
•
•
•
Standard-A plug and receptacle,
Standard-B plug and receptacle, and
Mini-B plug and receptacle.
The OTG supplement defines the following additional connectors:
•
•
Mini-A plug and receptacle, and
Mini-AB receptacle.
The Mini-A receptacle can only be used in the Mini-A receptacle to Standard-A plug adapter defined in
Section 4.5.7.1. All other uses are prohibited.
3.9
Compliant Cable Assemblies
The USB 2.0 specification defines the following cables:
•
•
•
6
Standard-A plug to Standard–B plug,
Standard-A plug to Mini-B plug, and
Captive cable with Standard-A plug.
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The OTG supplement defines the following additional cables:
•
•
•
Mini-A plug to Mini-B plug,
Mini-A plug to Standard-B plug, and
Captive cable with Mini-A plug.
No other types of cables are allowed by either the USB specification, or by the OTG supplement.
Cables are not allowed to have receptacles on either end unless they meet the mechanical and electrical
requirements of adapters defined in Section 4.5.7.
3.10 Plug Overmolds
The USB 2.0 specification limits the maximum size of the overmold for the Mini-B plug on the StandardA to Mini-B cable, but it does not define the shape of the overmold. The OTG supplement constrains the
size and the shape of the overmolds for the Mini-A plug. This supplement also constrains the size and
shape of the overmolds for the Mini-B plugs if those plugs are used on any of the new cables specified in
this supplement.
The Mini-A plug’s overmold has an oval theme, and the Mini-B plug’s overmold has a rectangular theme.
This allows easy recognition and differentiation of the two plugs by the consumer.
3.11 Cable Adapters
The OTG supplement defines the following cable adapters:
•
•
Mini-A receptacle to Standard-A plug, and
Standard-A receptacle to Mini-A plug.
The first adapter allows a captive cable device with a Mini-A plug to be connected to a standard host.
The second adapter allows a captive cable device with a Standard-A plug to be connected to a dual-role
device.
The physical and electrical properties of cable adapters are defined in Section 4.5.7.
3.12 Hubs
Dual-role devices may support hubs. However, the signaling methods used for the Session Request
Protocol and the Host Negotiation Protocol are not handled by standard USB hubs. Therefore, when an
A-device is directly connected to a standard hub, the A-device is prohibited from issuing a command that
would enable the downstream device to expect or initiate HNP.
3.13 Mandated Functionality
Any device with a Mini-AB receptacle shall meet all of the requirements and provide all the functionality
of a dual-role device.
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4. Mechanical
This chapter provides the mechanical and electrical specifications for the cables, connectors, and cable
assemblies used to interconnect devices.
4.1
Introduction
The USB 2.0 specification defines three connector pairs:
•
•
•
Standard-A plug and receptacle for the host;
Standard-B plug and receptacle for the peripheral; and
Mini-B plug and receptacle as alternative connectors for the peripheral.
This supplement defines the following connector components:
•
•
•
Mini-A plug,
Mini-A receptacle, and
Mini-AB receptacle.
The Mini-AB receptacle accepts either a Mini-A plug or a Mini-B plug.
This supplement defines the use of the new connector components on cables and adapters and permits
the following combinations:
•
•
•
•
•
Mini-A plug to Mini-B plug cable,
Mini-A plug to Standard-B plug cable,
Mini-A plug to captive cable,
Mini-A receptacle to Standard-A plug adapter, and
Standard-A receptacle to Mini-A plug adapter.
Constraints on the design of the overmolds for the Mini-A plugs are provided in this section.
Additionally, new constraints are placed on the design of the overmold for the Mini-B plugs when used
on a cable that also has a Mini-A plug.
4.2
Mini-Connector Mating
The following table summarizes the plugs accepted by each of the receptacles.
Table 4-1. Plugs Accepted By Receptacles
Receptacle
Plugs Accepted
Standard-A
Standard-A
Standard-B
Standard-B
Mini-B
Mini-B
Mini-A
Mini-A
Mini-AB
Mini-A or Mini-B
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The usage and wiring assignments of the five pins in the Mini-A plug are defined in the following table.
Table 4-2. Mini-A Plug Pin Assignments
Contact
Number
Signal Name
Typical Wiring
Assignment
1
VBUS
Red
2
D-
White
3
D+
Green
4
ID
< 10 Ω to GND
5
GND
Black
Shell
Shield
Drain Wire
The ID pin on a Mini-A plug shall be connected to the GND pin. The ID pin on a Mini-B plug is not
connected or is connected to ground by a resistance of greater than RB_PLUG_ID. A dual-role device is
required to be able to detect whether a Mini-A or Mini-B plug is inserted by determining if the ID pin
resistance to ground is less than RA_PLUG_ID or if the resistance to ground is greater than RB_PLUG_ID.
Any ID resistance less than RA_PLUG_ID shall be treated as ID = FALSE and any resistance greater than
RB_PLUG_ID shall be treated as ID = TRUE.
4.3
Color Coding
The following colors are mandated for the plastic inside the Mini connectors defined in this supplement.
Table 4-3. Color Coding for Plugs and Receptacles
Connector
4.4
Color
Mini-A receptacle
White
Mini-A plug
White
Mini-B receptacle
Black
Mini-B plug
Black
Mini-AB receptacle
Gray
Device, Cable and Adapter Delays
In Figure 7-11 of the USB 2.0 specification, four test planes are defined along the transmission path from
the host transceivers to the peripheral transceivers. These test planes (TP) are as follows:
•
•
•
•
10
TP1: pins of host transceiver chip
TP2: contact points of host Standard-A receptacle
TP3: contact points of peripheral Standard-B or Mini-B receptacle
TP4: pins of peripheral transceiver chip
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
June 24, 2003
Section 7.1.16 of the USB 2.0 specification states that the maximum allowed delays between these test
planes are:
•
•
•
TP1 to TP2:
TP2 to TP3:
TP3 to TP4:
3 ns
26 ns
1 ns
Since the OTG supplement allows the addition of an adapter to a cable, the delays between the test
planes for dual-role devices needs to be modified so that the maximum total delay between TP1 and
TP4 is 30 ns. The limits are as follows:
•
•
•
Dual-role device - TP1 to TP2:
Adapter:
Any cable with a Mini-A plug:
1 ns
1 ns
25 ns
The maximum delays for the two worst cases of connection are shown in the following tables.
Table 4-4. Maximum Delay for Mini-Connector and Cable
Location
Delay Time
USB 2.0 Compliant Host – TP1 to TP2
3 ns
Standard-A plug to Mini-A receptacle adapter
1 ns
Mini-A plug to Mini-B plug cable
25 ns
USB 2.0 Compliant B-device – TP3-TP4
1 ns
Total
30 ns
Table 4-5. Maximum Delay for Standard Connector Cable
Location
4.5
Delay Time
On-The-Go Compliant Dual-Role Device – TP1 to
TP2
1 ns
Mini-A plug to Standard-A receptacle adapter
1 ns
Standard-A plug to Standard-B plug cable
26 ns
USB 2.0 Compliant B-device – TP3 to TP4
1 ns
Total
29 ns
Compliant Usage of Connectors and Cables
Cable assemblies and connectors not described below or not allowed by other amendments to the USB
specification are not compliant with the USB specification and may not be labeled as such.
4.5.1
Cables
The new cables allowed by the OTG supplement are shown in Figure 4-1, Figure 4-2 and Figure 4-3. A
cable with a Mini-A plug must have a propagation delay of 25 ns or less, have a physical length of no
more than 4.5 meters, and meet all other requirements of a USB cable.
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4.5.2
June 24, 2003
Overmolds
The size and shape of the Mini-A plug overmold must conform to the constraints shown in Figure 4-4.
The size of a Mini-B plug used on a Standard-A to Mini-B cable must conform to the constraints shown
in Figure 6-10 in the Engineering Change Notice #1 of the USB Specification, version 2.0.
The size and shape of a Mini-B plug used in any other cable or adapter assembly must conform to the
constraints shown in Figure 4-5.
It is recommended that all new designs for the Mini-B plug overmold follow the constraints in Figure 4-5.
4.5.3
Mechanical Interfaces
The mechanical interfaces for the Mini-A plug, Mini-A receptacle and Mini-AB receptacle are shown in
Figure 4-6, Figure 4-7, Figure 4-8 and Figure 4-9.
4.5.4
Receptacle Reference Designs
Figure 4-10 and Figure 4-11 show reference designs for the Mini-A and Mini-AB receptacles
respectively. By following these recommendations, receptacles from different manufacturers can be
used interchangeably on the same printed circuit boards.
4.5.5
Connector Keying
This Mini connector series has been designed so as to prevent the Mini-A and Mini-B plugs from being
incorrectly inserted into a receptacle. The amount of metal blocking various possible incorrect insertions
is shown in Figure 4-12 and Figure 4-13, and is always greater than 0.35 mm.
4.5.6
Right Angle Plugs
The overmolds for right angle plugs are required to comply with the same shape constraints that apply to
straight plugs. Reference drawings for right angle plugs are shown in Figure 4-14, Figure 4-15, Figure
4-16 and Figure 4-17.
4.5.7
Adapters
The following adapters are permitted; all others are prohibited.
The propagation delay of the adapter shall be less than 1 ns. The physical length shall not exceed 150
mm. The resistance of the adapter through VBUS and GND, including contacts, shall not exceed 70 mΩ.
The only compliant adapters are:
•
•
Standard-A receptacle to Mini-A plug, and
Mini-A receptacle to Standard-A plug.
The reasons for not allowing a Series-B adapter include:
•
•
12
all legal connection topologies can be achieved with the defined cables and adapters, and
a Series-B adapter would make it possible to exceed the maximum TP1 to TP4 delay of 30 ns.
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
4.5.7.1
June 24, 2003
Mini-A receptacle to Standard-A plug
This adapter is used to connect a cable with a Mini-A plug to a USB host or hub with a Standard-A
receptacle. A reference drawing for this adapter is shown in Figure 4-18.
4.5.7.2
Standard-A receptacle to Mini-A plug
This adapter is used to connect a cable with a Standard-A plug to a dual-role device that has a Mini-AB
receptacle. A reference drawing for this adapter is shown in Figure 4-19.
4.6
Drawings
This section contains the mechanical drawings that are referenced in the previous section.
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Figure 4-1 Mini-A to Mini-B Cable
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June 24, 2003
Figure 4-2 Standard-B to Mini-A Cable
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Figure 4-3 Mini-A to Captive Cable
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June 24, 2003
Figure 4-4 Mini-A Plug Overmold, Straight
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Figure 4-5 Mini-B Plug Overmold, Straight
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June 24, 2003
Figure 4-6 Mini-A Plug Interface - 1 of 2
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Figure 4-7 Mini-A Plug Interface - 2 of 2
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June 24, 2003
Figure 4-8 Mini-A Receptacle Interface
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Figure 4-9 Mini-AB Receptacle Interface
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June 24, 2003
Figure 4-10 Mini-A Receptacle Reference Design
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Figure 4-11 Mini-AB Receptacle Reference Design
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Figure 4-12 Mini-A Plug Blockage
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Figure 4-13 Mini-B Plug Blockage
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June 24, 2003
Figure 4-14 Mini-A Plug, Side Right Angle
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Figure 4-15 Mini-A Plug, Down Right Angle
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June 24, 2003
Figure 4-16 Mini-B Plug, Side Right Angle
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Figure 4-17 Mini-B Plug, Down Right Angle
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Figure 4-18 Adapter, Standard-A receptacle to Mini-A plug
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Figure 4-19 Adapter, Mini-A receptacle to Standard-A plug
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5. Electrical Requirements
This section defines electrical specifications for USB devices that implement the protocols defined in this
specification. Any parameter that is not specified in this section is unchanged from the USB 2.0
specification.
5.1
A-Device Electrical Requirements
5.1.1
VBUS Output Voltage and Current
When an A-device is providing power to VBUS on a port, it is required to maintain an output voltage
(VA_VBUS_OUT) on that port between 4.4 V and 5.25 V, under loads of 0 mA up to the rated per port
output of the device’s supply (IA_VBUS_OUT min = 8 mA) as long as the rated output of the A-device is
less than or equal to 100 mA.
If the current rating per port of the A-device is greater than 100 mA, then the voltage regulation is
required to be between 4.75 V and 5.25 V, and the A-device is required to meet the USB 2.0
specification requirements for power providers.
If the A-device is not capable of providing at least 100 mA on a port, it must be able to detect when VBUS
falls below the value necessary for proper operation of a B-device (VA_VBUS_VLD min). Any voltage
below VA_VBUS_VLD min shall be detected as a low-voltage condition.
5.1.2
VBUS Input Impedance
When the A-device is powered and not providing VBUS, it shall present an input impedance on VBUS of
no more than 100 kΩ (RA_BUS_IN max) to GND over the range of 0 V ≤ VBUS ≤ 5.25 V, as shown in
Figure 5-1. If the A-device responds to the VBUS pulsing method of SRP, then the input impedance may
be no lower than 40 kΩ (RA_BUS_IN min) to GND. Otherwise, it may be lower.
131 uA
110 uA
Meets
Specification
in this area
I A_VBUS
Slope = 1 / 40 kohm s
53 uA
44 uA
Slope = 1 / 100 kohm s
0 uA
0V
4.4 V
5.25 V
V BUS
Figure 5-1 A-device Input Impedance (VBUS not driven)
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5.1.3
June 24, 2003
VBUS Rise and Fall Time
When the A-device provides power, the rise time on VBUS from 0 V to 4.4 V shall be less than 100 ms
(TA_VBUS_RISE max) when driving a constant current load equal to the rating of the device’s VBUS supply
and an external load capacitance of 10 µF (this 10 µF is in addition to any VBUS decoupling capacitance
on the A-device). If VBUS does not reach this voltage within TA_VBUS_RISE max from the time that VBUS
is turned on, this is an indication that the B-device is drawing more current that the A-device is capable
of providing and an over-current condition exists. In such a case, the A-device shall turn off VBUS and
terminate the session. The A-device shall also indicate to the user that the B-device is not supported.
Note: VBUS rise time is not specified in USB 2.0 and standard USB hosts may have rise times longer
than 100 ms. A compliant device shall be able to operate with the longer VBUS rise times allowed by
the USB 2.0 specification.
The fall time of VBUS is derived and not specified. It is only significant when the B-device initiates and
the A-device responds to SRP. Before starting SRP, the B-device must insure that VBUS is below 0.8 V.
The B-device may either actively pull down VBUS through a resistance of no less than RB_SRP_DWN min
(see Section 5.3.2), or it may wait for the decoupling capacitance of the A-device and B-device to
discharge through the weak pull-downs that are present on VBUS.
For an A-device, the highest pull-down resistance on VBUS is 100 kΩ (RA_BUS_IN max) and the
decoupling capacitance is less than 6.5 µF (CDRD_VBUS max). The values of the decoupling capacitor
and the VBUS pull-down resistor on the B-device are known by the manufacturer of the B-device. These
values are used with the worst-case values of the A-device in computing the discharge time for VBUS. If
the worst-case values on the B-device are the same as for the A-device, then the longest discharge time
from 4.4 V (VA_VBUS_VLD min) to 0.8 V (VA_SESS_VLD min) will be approximately 1.1 seconds.
5.1.4
VBUS Capacitance
A dual-role device must have a VBUS capacitance (CDRD_VBUS) that is between 1.0 µF and 6.5 µF.
The limit on the decoupling capacitance allows a B-device to differentiate between a powered down
dual-role device and a powered down standard host, i.e.:
•
•
5.1.5
Capacitance on A-Device
Capacitance on Host
1.0 µF < CDRD_VBUS < 6.5 µF
CHST_VBUS > 96 µF
VBUS Leakage Voltage
When the A-device is not driving VBUS, the voltage on VBUS as a result of device leakage within the Adevice (VA_VBUS_LKG) shall not exceed 0.2 V. This voltage is measured with no device attached to the
A-device and after VBUS has been turned off for 5 seconds.
5.1.6
Data Line Pull-down Resistance
When an A-device is idle or acting as Host, it shall activate pull-down resistors on both the D+ and Dlines. These resistors shall be within the range of 14.25 kΩ to 24.8 kΩ (RPD).
When an A-device is acting as a Peripheral, it shall disable the pull-down on the D+ line but shall not
disable the pull-down on the D- line.
The A-device is allowed to disable both pull-down resistors during the interval of a packet transmission,
when acting as either Host or Peripheral.
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5.1.7
June 24, 2003
Data Line Pull-up Resistance
When operating as a Peripheral, the A-device shall enable a pull-up (as defined in the USB 2.0
specification) attached to the D+ line. It is allowed to disable the pull-up resistor during the interval of a
packet transmission.
5.1.8
Data Line Leakage Voltage
When neither device is driving the data bus, one of the data lines will be held low by the pull-down
resistor on the Host. The D- line is pulled low if the attached device is full speed and D+ line is pulled
low if the attached device is low speed.
The low-level voltage on the line that is being pulled low may not be above 0.342 V (VDRD_DATA_LKG
max). As per Section 7.1.6.6 of the USB 2.0 specification, the attached device may have an impedance
as low as 300 kΩ (ZINP min) to 3.6 V. When the data line of the attached device is grounded, this results
in a leakage current of approximately 10 µA. The leakage current from the Host shall be low enough
such that, when combined with the approximately 10 µA of leakage from the attached device, the
voltage across the pull-down resistor shall not exceed 0.342 V. This voltage is measured by pulling
either D+ or D- to 3.6 V through 300 kΩ (ZINP min) when the A-device is the Host and the bus is in the
idle state.
5.1.9
Data Line Discharge Time
When an A-device is in the a_peripheral state and detects that the bus is idle for greater than
TA_BIDL_ADIS, then it is allowed to:
•
•
•
disconnect its pull up
allow time for the data line to discharge
check if the B-device has connected its pull up
Similarily, when a B-device is in the b_peripheral state and detects that the bus is idle for greater than
TB_AIDL_BDIS, then it is allowed to:
•
•
•
disconnect its pull up
allow time for the data line to discharge
check if the A-device has connected its pull up
During the above steps, the amount of time that the local device must wait for the data line to discharge,
before checking to see if the remote device has connected its pull up, is determined as follows.
As per Table 7-7 of the USB 2.0 specification, the maximum capacitance for a downstream facing port is
150 pF (CIND max), and the maximum capacitance for the upstream port of a device without an attached
cable is 100 pF (CINUB max). The differential capacitance of a worst-case USB cable is approximately
340 pF (the single-ended capacitance is lower but is not specified so assuming that the single-ended
capacitance is the same as the differential capacitance will insure a worst case calculation). The pulldown resistance of each dual-role device is 24.8 kΩ (RPD max) or less. This results in a discharge time
constant of:
•
time constant = (150 pF + 100 pF + 340 pF) x (24.8 kΩ / 2) ≈ 6.7 µsec
For the data line to discharge from 3.6 V to 0.8 V requires approximately 1.55 time constants. This gives
a worst case delay for the data line discharge of about 10.4 µs. In previous cases of USB specification
development, time values for RC charge/discharge were used to set timing values. In most cases, these
values did not have a large margin for error or to allow for simple variations in implementation to reduce
costs or complexity. For this reason, the guard-band for the data-line discharge is set at about 2.5 times
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June 24, 2003
the calculated value. Thus, if a device uses this method to ensure the data line is at a logic low level, it
must wait for a minimum of TLDIS_DSCHG min before checking the state of the data-line.
5.1.10 VBUS Input Current Without Battery
In many cases, dual-role devices will be powered by a battery. When a dual-role device has a dead
battery that is not capable of powering up the device, or if the battery has been removed, then a dualrole device is allowed to act as a peripheral in accordance with the USB 2.0 specification. See Figure 729 and section 7.1.7.6 of the USB 2.0 specification for rules on current draw.
5.2
B-Device Electrical Requirements
5.2.1
VBUS Average Input Current
An unconfigured, dual-role B-device shall not draw more than IB_DRD_UNCFG max average current from
VBUS, except for a short interval immediately before initiating SRP.
An unconfigured, SRP capable, peripheral-only B-device shall not draw more than IB_PO_UNCFG max
average current from VBUS.
Average current as used above is defined as the average current over any 1 ms interval.
Before initiating SRP, either a dual-role or an SRP capable peripheral-only B-device is allowed to
discharge VBUS for a time period of not more than 100 ms, at a current of not more than IB_DSCHG_IN
max.
5.2.2
VBUS Peak Input Current
The peak current drawn by an SRP capable B-device shall not be so large as to cause more than a
VB_DELTA_PK drop in VBUS from its average value. The allowable transient is computed by assuming
that the A-device is a constant current source providing the average current consumed by the B-device
in parallel with a CDRD_VBUS min capacitor.
The 1 µF decoupling capacitor on the A-device and the decoupling capacitor provided on he B-device
will provide the only filtering of the voltage transient due to the transient current. If the transient current
computed by this method is greater than 100 mA, then the transient shall be no larger than the larger of
100 mA or the value reported in bMaxPower in the currently selected configuration. No transient shall
have a di/dt of greater than 100 mA/µs. (For reference, see Figure 7-48 of USB 2.0 specification.)
The peak current drawn by an SRP capable B-device shall not cause it to exceed the average current
requirement as defined in Section 5.2.1.
5.2.3
VBUS Capacitance
The VBUS capacitance allowed for a dual-role B-device is the same as that allowed for an A-device, (see
Section 5.1.4).
5.2.4
Data Line Pull-down Resistance
When a dual-role B-device is idle or acting as a Host, it shall activate pull-down resistors on both the D+
and D- lines. These resistors shall be within the range of 14.25 kΩ to 24.80 kΩ (RPD).
When a dual-role B-device is acting as a Peripheral, it shall disable the pull-down on the D+ line but shall
not disable the pull-down on the D- line.
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A dual-role B-device is allowed to disable both pull-down resistors during the interval of a packet
transmission while acting as either a Host or a Peripheral.
5.2.5
Data Line Pull-up Resistance
When operating as Peripheral, the B-device shall enable a pull-up (as defined in the USB 2.0
specification) attached to the D+ pin. It is allowed that the pull-up resistor be disabled during the interval
of a packet transmission.
5.2.6
Data Line Leakage Voltage
For a dual-role B-device, the data line leakage voltage shall be as specified in Section 5.1.8 for an Adevice.
5.2.7
VBUS Input Current Without Battery
If an SRP capable peripheral has a dead battery, or the battery has been removed, then it is allowed to
act as a peripheral in accordance with the USB 2.0 specification, and as described in Section 5.1.3.
5.3
Session Request Protocol
5.3.1
Introduction
In order to conserve power, the OTG supplement allows an A-device to leave VBUS turned off when the
bus is not being used. If the B-device wants to use the bus when VBUS is turned off, then it requires
some way of requesting the A-device to supply power on VBUS. For this reason, the OTG supplement
defines the Session Request Protocol (SRP).
A session is defined as the period of time that VBUS is above the Session Valid threshold of a given
device. This A-device threshold shall be within the range defined by VA_SESS_VLD, while the B-device
threshold shall be in the range defined by VB_SESS_VLD, (see Table 5-1). At the start of a session, the Adevice defaults to having the role of Host. During a session, the role of Host can be transferred back
and forth between the A-device and the B-device any number of times, using the Host Negotiation
Protocol (HNP) defined in Section 6. The session ends when VBUS falls below the A-device Session
Valid threshold.
Dual-role devices are required to be able to initiate and respond to SRP. Any A-device, including a PC
or laptop, is allowed to respond to SRP. Any B-device, including a standard USB peripheral, is allowed
to initiate SRP.
The OTG supplement defines two methods that are used by the B-device to request that the A-device
begin a session. They are called “data-line pulsing” and “VBUS pulsing”. These two methods comprise
the Session Request Protocol (SRP).
Two signaling methods are defined to allow maximum latitude in the design of A-devices. An A-device is
only required to respond to one of the two SRP signaling methods. A B-device shall use both methods
when initiating SRP to insure that the A-device responds.
5.3.2
Initial Conditions
The B-device may not attempt to start a new session until it has determined that the A-device should
have detected the end of the previous session. The A-device detects the end of a session by sensing
that VBUS has dropped below its session valid threshold. Since the A-device Session Valid threshold
may be as low as VA_SESS_VLD min, the B-device must insure that VBUS is below this level before
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requesting a new session. The B-device may ensure that VBUS is below the B-device Session End
threshold either by direct measurement of VBUS or by timing the discharge.
Additionally, the B-device may switch in a pull-down resistor from VBUS to ground in order to speed the
discharge process as long as the pull-down resistor does not cause the B-device to draw more than 8
mA from VBUS. To ensure this, the resistance of the pull-down (RB_SRP_DWN) must be greater than 656
Ω, (5.25 V / 8 mA = 656 Ω).
A second initial condition for starting a new session is that the B-device must detect that both the D+ and
D- data lines must have been low (SE0) for at least TB_SE0_SRP min. This ensures that the A-device has
detected a disconnect condition from the device.
These initial conditions define the period after which the A-device will properly recognize SRP from the
B-device.
Each B-device is required to have a Session End threshold that is within the Session End range
(VB_SESS_END) defined in Table 5-1. This threshold can be implemented directly, as with a comparator,
or it can be implemented indirectly, by timing a discharge of VBUS through a resistor. The reason that
Table 5-1 lists a lower limit of 0.2V on this threshold is that leakage currents from the transceivers could
prevent a non-driven VBUS from discharging below this lower voltage.
When the B-device detects that VBUS has gone below its Session End threshold and detects that both
D+ and D- have been low (SE0) for at least TB_SE0_SRP min, then any previous session on the A-device
is over and a new session may start.
5.3.3
Data-line Pulsing
To indicate a request for a new session using the data-line pulsing SRP, the B-device waits until the
initial conditions are met as described above and then turns on its data line pull-up resistor (either D+ or
D-) for a period of TB_DATA_PLS min to TB_DATA_PLS max. A dual-role B-device is only allowed to initiate
SRP at full-speed, and thus shall only pull up D+. The duration of such a data line pulse is sufficient to
allow the A-device to reject spurious voltage transients on the data lines.
An A-device that is designed to detect the data-line pulsing of SRP shall generate an SRP indication if
either D+ goes high or D- goes high.
Note: It has been observed that some self-powered USB devices do not follow USB Revision 1.1
Section 7.1.5 or USB Revision 2.0 Section 7.1.5.1 that state:
“The voltage source on the pull-up resistor must be derived from or
controlled by the power supplied on the USB cable such that when
VBUS is removed, the pull-up resistor does not supply current on the
data line to which it is attached.”
Devices that violate the above requirement have been observed to pull-up D+ or D- as long as they
have power applied to them, without regard to the presence of VBUS. For this reason, a dual-role
device that responds to data-line pulsing SRP should be able to disable this capability when an
offending device is attached. The process for handling this would be to start a session upon
detecting D+/D- high, enumerate the device, determine that it is not supported, disable SRP, and
turn off VBUS. When the data line returns low (indicating a disconnect), then SRP should be reenabled.
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5.3.4
June 24, 2003
VBUS Pulsing
To indicate a request for a new session using the VBUS pulsing method, the B-device waits until the
initial conditions are met as described in Section 5.3.2 and then drives VBUS. VBUS is driven for a period
that is long enough for a capacitance on VBUS that is smaller than 13 µF ( 2 x CDRD_VBUS max) to be
charged to VB_DRD_OUT min while a capacitance on VBUS of more than 97 µF (CHST_VBUS min +
CDRD_VBUS min) will not be charged above 2.0 V (VB_HST_OUT max).
There are two scenarios that a B-device could encounter when pulsing VBUS to initiate SRP. In one
scenario, the B-device is connected to an A-device that responds to the VBUS pulsing SRP. In this case,
the B-device can drive VBUS above the A-device Session Valid threshold in order to wake up the Adevice. (This assumes that the A-device is not already driving VBUS, in which case a session is already
in progress). When driving such an A-device, the B-device shall ensure that VBUS goes above 2.1 V
(VB_DRD_OUT min), but does not exceed 5.25 V (VB_DRD_OUT max).
In the second scenario, the B-device is attached to a standard host. In this case, the B-device shall not
drive VBUS above 2.0V (VB_HST_OUT max). This insures that no damage is done to standard hosts that
are not designed to withstand a voltage externally applied to VBUS.
In order to meet these requirements, the B-device can utilize the fact that the capacitance on a standard
host will not be less than 96 µF (CHST_VBUS min), while the maximum capacitance allowed on a dualrole device is 6.5 µF (CDRD_VBUS max). Based on the greater than one order-of-magnitude difference
between these two capacitances, and a self-imposed current limit, the B-device designer can derive a
maximum length of time the B-device is allowed to drive VBUS. By driving VBUS for this duration, the
designer can guarantee that VBUS will rise above 2.1 V if attached to a dual-role device, while ensuring
that VBUS will not exceed 2.0 V if attached to a standard USB host.
5.3.5
B-Device VBUS Pulsing Current
The B-device VBUS pulsing circuitry must be designed such that the maximum current drawn by the Bdevice does not exceed 8 mA (IB_SO_UNCFG max). One way to ensure this restriction is met is to drive
VBUS with a voltage source greater than 3.0 V and with an output impedance greater than 281 Ω
(RB_SRP_UP min). This takes into consideration the possibility that if the A-Device responds very quickly
to SRP, it could drive VBUS to 5.25 V while the B-device is still pulsing VBUS. If this happened, then
current could flow from the 5.25 V on the A-device back to the 3.0 V on the B-device. ([5.25 V – 3.0 V]/8
mA ≅ 281 Ω)
5.3.6
A-Device Session Valid
The A-device continuously monitors VBUS as long as power is available on the A-device. An A-device
that is designed to detect the VBUS pulsing method will detect that VBUS has gone above the A-device
Session Valid threshold (VA_SESS_VLD) and generate an indication that SRP has been detected.
5.3.7
B-Device Session Valid
When a B-device detects that the voltage on VBUS is greater than the B-Device Session Valid threshold
(VB_SESS_VLD), then the B-device shall consider a session to be in progress. After the VBUS voltage
crosses this threshold, the B-device shall assert either the D+ or D- data-line within 1 second
(TB_SVLD_BCON max).
5.3.8
Duration of SRP
The maximum time allowed for the B-device to complete all of its SRP initiation activities is 100 ms
(TB_SRP_INIT max). The SRP activities include all those activities that transpire while the B-device is not
monitoring the state of VBUS. The B-device shall not monitor VBUS when doing VBUS pulsing but it may
continue to monitor VBUS during the period of time when it is pulling VBUS down and during data-line
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June 24, 2003
pulsing. If VBUS is monitored during these periods, then the time taken for them is not counted in the 100
ms limit for SRP activities.
5.3.9
Order of Methods
The B-device shall first perform data-line pulsing, followed by VBUS pulsing.
5.3.10 Response Time of A-device
The A-device may be designed to respond to either of the methods of SRP. After initiating SRP, the Bdevice is required to wait at least 5 seconds (TB_SRP_FAIL min) for the A-device to respond, before
informing the user that the communication attempt has failed. For this reason, it is recommended that
the A-device respond to SRP in less than 5 seconds (TA_SRP_RSPNS max). The minimum response from
the A-device is to turn on VBUS and generate a bus reset.
5.3.11 Repetition of SRP
The B-device may initiate the SRP any time the initial conditions of Section 5.3.2 are met.
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5.4
June 24, 2003
Electrical Characteristics
Table 5-1. DC Electrical Characteristics
Parameter
Symbol
Conditions
Min
Max
Units
Ref
5.25
V
5.1.1
100
ms
5.1.3
0.2
V
5.1.5
5.25
V
5.3.4
2.0
V
5.3.4
400
mV
5.2.2
mA
5.1.1
VBUS Voltage:
A-Device Output Voltage
VA_VBUS_OUT
0 ≤ IVBUS ≤
IA_VBUS_OUT <
100 mA
VBUS Rise Time
TA_VBUS_RISE
CLOAD = 10 µF
IVBUS = rated load1
0.0 V < VBUS < 4.4 V
A-device Leakage Voltage
VA_VBUS_LKG
B-device (SRP capable) to
Dual-Role Device Output
Voltage
VB_DRD_OUT
B-device (SRP capable) to
Host Output Voltage
VB_HST_OUT
B-device (SRP capable)
Induced Transient
VB_DELTA_PK
di/dt < 100 mA/µs
A-Device Output Current
IA_VBUS_OUT
4.4 V ≤ VBUS ≤ 5.25
V
B-Device (Dual-Role)
Unconfigured Average Current
IB_DRD_UNCFG
0 V ≤ VBUS ≤ 5.25 V
TAVG = 1 ms
150
µA
5.2.1
B-Device (SRP capable,
Peripheral-Only) Unconfigured
Average Current
IB_PO_UNCFG
0V ≤ VBUS ≤ 5.25 V
TAVG = 1 ms
8
mA
5.2.1
B-Device (SRP capable)
Discharge Current
IB_DSCHG_IN
0 V ≤ VBUS ≤ 5.25 V
8
mA
5.2.1
.342
V
5.1.8
Ω
4.2
Ω
4.2
4.4
2.1
VBUS Current:
8
Data-Line Voltage:
Dual-Role Device Leakage
VDRD_DATA_LKG
ID Resistance:
Resistance to ground on MiniB plug
RB_PLUG_ID
Resistance to ground on MiniA plug
RA_PLUG_ID
100K
10
1
Each implementation must be capable of supplying a minimum of 8mA of VBUS. An implementation
that is designed to provide more than 8 mA shall be able to meet the rise-time requirement for VBUS
when the applied load is equal to the design limit of the supply.
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Table 5-1. DC Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Max
Units
Ref
Terminations:
A-device Data Line Pull-down
RPD
14.25
24.8
kΩ
5.1.6
B-device Data Line Pull-down
RPD
14.25
24.8
kΩ
5.2.4
A-Device VBUS Input
Impedance to GND
RA_BUS_IN
SRP capable Adevice, not driving
VBUS
40
100
kΩ
5.1.2
B-device VBUS SRP pull-up
RB_SRP_UP
Pull-up voltage = 3.0 V
281
Ω
5.3.5
B-device VBUS SRP pull-down
RB_SRP_DWN
656
Ω
5.3.2
A-device VBUS Valid
VA_VBUS_VLD
4.4
V
5.1.1
A-Device Session Valid
VA_SESS_VLD
0.8
2.0
V
5.3.6
B-Device Session Valid
VB_SESS_VLD
0.8
4.0
V
5.3.7
B-Device Session End
VB_SESS_END
0.2
0.8
V
5.3.2
CDRD_VBUS
1
6.5
µF
5.1.4
Input Levels:
Decoupling Capacitance:
Dual-role Device VBUS Bypass
Capacitance
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5.5
June 24, 2003
Device Timings
Table 5-2lists the timing parameters of an A-device. The parameters are listed in roughly the order that
they would occur during the following sequence of events.
•
•
•
A-device responds to SRP and becomes Host
A-device suspends the bus and B-device becomes Host
B-device suspends the bus and A-device becomes Host
In case of a discrepancy between a parameter value as listed in the table below, and it’s value as listed
in other parts of the document, the table value shall take precedence.
The states listed in the table are described in Section 6.
Table 5-2. A-device Timing
Parameter
SRP Response Time
Num
1
Symbol
TA_SRP_RSPNS
State
Min1
a_idle
Max1
Units
30
sec
5.3.10
ms
6.6.5.1
ms
6.6.1.12
sec
6.8.1.3
2
Ref
Wait for VBUS Rise
2
TA_WAIT_VRISE
a_wait_vrise
B-Connect Long Debounce
3
TA_BCON_LDB
a_wait_bcon
B-connect to A-reset
3
TA_BCON_ARST
a_wait_bcon
Wait for B-Connect
4
TA_WAIT_BCON
a_wait_bcon
1
sec
6.6.5.2
A-Idle to B-Disconnect
5
TA_AIDL_BDIS
a_suspend
200
ms
6.6.5.3
B-Disconnect to A-Connect
6
TA_BDIS_ACON
a_suspend
3
ms
6.3
B-Idle to A-Disconnect
7
TA_BIDL_ADIS
a_peripheral
3
200
ms
6.3
Local Disconnect to Data
Line Discharge
8
TLDIS_DSCHG
a_wait_bcon
25
µs
5.1.9
B-Connect Short Debounce
9
TA_BCON_SDB
a_wait_bcon
2.5
µs
6.6.1.12
B-Connect Short Debounce
Window
10
TA_BCON_SDB_WIN
a_wait_bcon
ms
6.6.1.12
100
100
30
100
1
Time values are presumed to have precision and accuracy to within 2,500 ppm for FS capable devices
and 500 ppm for HS capable devices.
2
This value is vendor dependent. A compliant A-device will be capable of bringing VBUS in tolerance
within no more than 100ms and waiting longer for VBUS rise is not advisable. If the vendor has designed
the power supply to bring VBUS within tolerance in less than 100 ms, then it is appropriate to adjust this
value downward to meet the capabilities of the implementation.
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Table 5-3 lists the timing parameters of an A-device. The parameters are listed in roughly the order that
they would occur during the following sequence of events.
•
•
•
B-device initiates SRP and becomes Peripheral
A-device suspends and B-device becomes Host
B-device suspends and A-device becomes Host
In case of a discrepancy between a parameter value as listed in the table, and it’s value as listed in other
parts of the document, the table value shall take precedence.
Table 5-3. B-device Timing
Parameter
Num
Symbol
State
Min1
SE0 Time Before SRP
11
TB_SE0_SRP
b_idle
2
Data-Line Pulse Time
12
TB_DATA_PLS
b_srp_init
5
SRP Initiate Time
13
TB_SRP_INIT
b_srp_init
SRP Fail Time
14
TB_SRP_FAIL
b_srp_init
Session Valid to B-Connect
15
TB_SVLD_BCON
b_idle
A-Idle to B-Disconnect
16
TB_AIDL_BDIS
b_peripheral
Time between B-device HS
to FS transition during
suspend, and B-device
disconnect
17
TB_FS_BDIS
Local Disconnect to Data
Line Discharge
18
TLDISC_DSCHG
Units
Ref
ms
5.3.2
10
ms
5.3.3
100
ms
5.3.8
30
sec
6.8.2.2
1
sec
5.3.7
5
150
ms
6.3
b_peripheral
1
147
ms
6.3
b_wait_acon
25
µs
5.1.9
ms
6.7.1
µs
6.6.1.5
ms
6.3
5
A-SE0 to B-Reset
19
TB_ASE0_BRST
b_wait_acon
3.125
A-Connect Debounce
20
TB_ACON_DBNC
b_wait_acon
2.5
A-Connect to B-SE0
21
TB_ACON_BSE0
b_wait_acon
1
Max1
as
per
USB
2.0
1
Time values are presumed to have precision and accuracy to within 2,500 ppm for FS capable devices
and 500 ppm for HS capable devices.
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1
2
4
3
Bus Reset
VIH
Data Line
VIL
4.4 V
VBUS
2.0 V
VA_SESS_VLD
0.8 V
Legend
Driven by A-device
A-device pull-down
Driven by B-device
B-device pull-up
Figure 5-2 A-device SRP Timing Reference
10
5
6
8
VOH
A-device
VOL
7
VOH
B-device
VOL
Bus Reset
9
Bus Reset
VIH
Composite D+
VIL
Driven
Legend
Normal bus traffic
Pull-down
Pull-up
Figure 5-3 A-device HNP Timing Reference (FS)
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10
5
6
8
VOH
A-device
VOL
HS
HS
HS
VOH
B-device
VOL
7
HS
HS
HS
Bus Reset
9
Bus Reset
VIH
Composite D+
VIL
HS
HS
Driven (FS)
Driven (HS)
Legend
Pull-down
HS
HS
Pull-up
Normal bus traffic
Figure 5-4 A-device HNP Timing Reference (HS)
At several points during SRP and HNP, one device is allowed a maximum length of time to respond to
an event, while the other device is required to wait a minimum length of time for this response. Table
5-4 compares the maximum response time of one device to the minimum wait time of the other device.
In case of a discrepancy between Table 5-4 and the values in Table 5-2and Table 5-3, the values in
Table 5-2and Table 5-3 take precedence.
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Table 5-4. Device Timing Comparison
Device
Parameter
Symbol
State
Min1
Max1
Units
B-device
SRP Initiate Time
TB_SRP_INIT
b_srp_init
100
ms
B-device
Session Valid Voltage to
Local Connect
TB_SVLD_BCON
b_idle
1
sec
A-device
Wait for B-Connect
TA_WAIT_BCON
a_wait_bcon
A-device
SRP Response Time
TA_SRP_RSPNS
a_idle
B-device
SRP Fail Time
TB_SRP_FAIL
b_idle
B-device
A-Idle to B-Disconnect
TB_AIDL_BDIS
A-device
A-Idle to B-Disconnect
A-device
B-Disconnect to A-Connect
1.2
sec
30
sec
5
30
sec
b_peripheral
5
150
ms
TA_AIDL_BDIS
a_suspend
200
TA_BDIS_ACON
a_suspend
3
ms
as
per
USB
2.0
ms
1
ms
200
ms
B-device
A-SE0 to B-Reset
TB_ASE0_BRST
b_wait_acon
B-device
A-Connect to B-SE0
TB_ACON_BSE0
b_wait_acon
A-device
B-Idle to A-Disconnect
TA_BIDL_ADIS
a_peripheral
3.125
3
ms
1
Time values are presumed to have precision and accuracy to within 2,500 ppm for FS capable devices
and 500 ppm for HS capable devices.
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Bus Reset
11
12
15
VIH
Data Line
VIL
14
4.4 V
13
VBUS
2.0 V
VB_SESS_VLD
0.8 V
Legend
Driven by A-device
A-device pull-down
Driven by B-device
B-device pull-up
Figure 5-5 B-device SRP Timing Reference
16
VOH
A-device
VOL
18
21
VOH
B-device
VOL
20
Bus Reset
VIH
Composite D+
VIL
Driven
Normal bus traffic
Legend
Pull-down
Pull-up
Figure 5-6 B-device HNP Timing Reference (FS)
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16
VOH
VOH
A-device
VOL
HS
HS
VOL
HS
19
18
VOH
VOH
B-device
VOL
HS
HS
17
21
VOL
HS
Bus Reset
VIH
VIH
Composite D+
VIL
HS
HS
20
Driven (FS)
Legend
Pull-down
Driven (HS)
Pull-up
VIL
HS
HS
Normal bus traffic
Figure 5-7 B-device HNP Timing Reference (HS)
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6. Host Negotiation Protocol
6.1
Introduction
Since dual-role devices have a Mini-AB receptacle, a dual-role device can default to being either Host or
Peripheral, depending up which type of plug (Mini-A plug for Host, Mini-B plug for Peripheral) is inserted.
By utilizing the Host Negotiation Protocol (HNP), a dual-role B-device, which is the default Peripheral,
may make a request to be Host. The process for this exchange of the role of Host is described in this
section. This protocol eliminates the need for the consumer to swap the cable connection in order to
change the roles of the connected devices.
6.2
Description Priority
HNP and SRP are described in this section by each of the following methods:
•
•
state diagrams
text
In the case of a conflict between these two descriptions, the state diagrams shall take precedence.
It should be noted that the state diagrams are presented to show one possible implementation of the
HNP and SRP protocols. An implementation that exhibits an equivalent behavior as observed at the
USB connector pins would also be considered to be in compliance with this specification.
6.3
HNP Overview
HNP is used to transfer control of a connection from the default Host (A-device) to the default Peripheral
(B-device). This is accomplished by having the A-device condition the B-device to be able to take
control of the bus, and then having the A-device present an opportunity for the B-device to take control.
The B-device is conditioned when the A-device sends a SetFeature(b_hnp_enable) command. After
sending this command, the A-device may suspend the bus to signal the B-device that it may now take
control of the bus. If the B-device wants to use the bus at that time, it signals a disconnect to the Adevice. If the A-device has enabled the B-device to become Host, then the A-device will interpret this
disconnect during suspend as a request from the B-device to become Host. The A-device will complete
the handoff by turning on it’s pull-up resistor on D+.
When the B-device has finished using the bus, it starts the process of returning control to the A-device
simply by stopping all bus activity and turning on its D+ pull-up resistor when the bus is in FS idle. The
A-device will detect this lack of activity and turn off its pull-up resistor. When the A-device detects the
connection from the B-device, it will resume bus operation as Host.
The sequence of events for HNP as observed on the USB are illustrated in Figure 6.1.
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A-device
A
F
H
C
B-device
B
D
E
G
D+ Com posite
Legend
D+ driven
Pull-up dom inates
Pull-down dom inates
Norm al bus activity
Figure 6-1 HNP Sequence of Events
A) A-device finishes using bus and stops all bus activity, (i.e. suspends the bus).
B) B-device detects that bus is idle for more than TB_AIDL_BDIS min and begins HNP by turning off pullup on D+. This allows the bus to discharge to the SE0 state. If the bus was operating in HS mode,
the B-device will first enter the full-speed mode and turn on its D+ pull-up resistor for at least
TB_FS_BDIS min before turning off its pull up to start the HNP sequence.
Note: After B-device enters the FS mode and turns on its pull-up resistor; it waits to see if the
data line goes high. If the data line does not go high within TWTRSTHS (from Table 7-14 in
USB 2.0 specification), then the B-device shall start its HS chirp. Otherwise, if the D+ line does
go high for at least TB_FS_BDIS min, then the B-device may start HNP.
C) The A-device detects the SE0 on the bus and recognizes this as a request from the B-device to
become Host. The A-device responds by turning on its D+ pull-up within TA_BDIS_ACON max of first
detecting the SE0 on the bus.
D) After waiting long enough to insure that the D+ line cannot be high due to the residual effect of the
B-device pull-up, (see Section 5.1.9), the B-device sees that the D+ line is high and D- low, (i.e. J
state). This indicates that the A-device has recognized the HNP request from the B-device. At this
point, the B-device becomes Host and asserts bus reset to start using the bus. The B-device must
assert the bus reset (SE0) within TB_ACON_BSE0 max of the time that the A-device turns on its pullup.
E) When the B-device completes using the bus, it stops all bus activity. (Optionally, the B-device may
turn on its D+ pull-up when a FS idle condition is detected on the bus.)
F) A-device detects lack of bus activity for more than TA_BIDL_ADIS min and turns off its D+ pull-up.
Alternatively, if the A-device has no further need to communicate with the B-device, the A-device
may turn off VBUS and end the session.
G) B-device turns on its pull-up.
H) After waiting long enough to insure that the D+ line cannot be high due to the residual effect of the
A-device pull-up, (see Section 5.1.9), the A-device sees that the D+ line is high (and D- low)
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indicating that the B-device is signaling a connect and is ready to respond as a Peripheral. At this
point, the A-device becomes Host and asserts bus reset to start using the bus.
6.4
OTG Descriptor
During enumeration, a dual-role A-device shall request the OTG configuration descriptor from the Bdevice. Any B-device that supports either HNP or SRP must respond by providing this descriptor in the
group of descriptors returned in response to a GetDescriptor(Configuration) command. When present,
the OTG descriptor shall be present in all configurations. This three-byte descriptor consists of three
fields: bLength, bDescriptorType, and bmAttributes, with bits as defined in the following table.
Table 6-1. OTG Descriptor
Offset
6.4.1
Field
Size
Value
Description
0
bLength
1
Number (3)
Size of Descriptor
1
bDescriptorType
1
Constant
OTG type = 9
2
bmAttributes
1
Bitmap
Attribute Fields
D7…2: Reserved (reset to zero)
D1: HNP support
D0: SRP support
srp_support
This bit is set to TRUE if the device supports SRP. This bit is not used by the A-device during normal
operation. However, this bit is used during compliance testing to automatically detect the capabilities of
the B-device.
6.4.2
hnp_support
This bit is set to TRUE if the device supports HNP. If the hnp_support bit is TRUE, then srp_support must
also be TRUE.
6.5
Set Feature Commands
An A-device may use the SetFeature command to enable certain behaviors on the B-device or to
indicate certain capabilities of the A-device to the B-device. Any HNP capable device is required to
accept the SetFeature commands for these features. If the device is not HNP capable, it shall return
STALL if it receives a SetFeature command for any of these features
A B-device that supports these features shall be able to accept the SetFeature command in the Default,
Address and Configured states. (It should be noted that the USB 2.0 specification states that setting a
feature in the Default state for other than test modes is unspecified. This supplement adds to the list of
features that can be set in the Default state.)
Setting one of these features when it is already set is not an error. The device receiving such a
command will acknowledge the command indicating successful completion.
A SetFeature command for these features shall be executed on receipt of an uncorrupted command
packet.
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Table 6-2. Set Feature Command Format
bmRequestType
bRequest
Wvalue
wIndex
wLength
Data
00000000B
SET_FEATURE
Feature
Selector
Zero
Zero
None
Table 6-3. On-The-Go Feature Selectors
Feature Selector
6.5.1
Value
b_hnp_enable
3
a_hnp_support
4
a_alt_hnp_support
5
b_hnp_enable
Setting this feature indicates to the B-device that it has been enabled to perform HNP. An A-device may
set this feature if, and only if, the B-device is connected directly to an A-device port that supports HNP
(i.e. no intervening hub between the Host and the B-device).
The b_hnp_enable feature takes precedence over either the a_hnp_support or a_alt_hnp_support
features. Thus, if b_hnp_enable is set, then HNP is enabled in the B-device, regardless of whether or
not the a_hnp_support or a_alt_hnp_support bits are set.
This feature is only cleared on a bus reset or at the end of a session. It cannot be cleared with a
ClearFeature(b_hnp_enable) command.
6.5.2
a_hnp_support
Setting this feature indicates to the B-device that it is directly connected to an A-device port that supports
HNP.
The A-device shall set this feature on any B-device that is connected to an A-device port that supports
HNP. The A-device shall set this feature at the start of a session, before any B-device configuration is
selected.
If the A-device port that is connected to the B-device is not HNP capable, then the A-device shall not set
this feature.
Before putting the B-device into a configuration, the A-device has the following three options with
regards to the b_hnp_enable and a_hnp_support features:
•
•
•
set the b_hnp_enable feature
set the a_hnp_support feature but not the b_hnp_enable feature
set neither the b_hnp_enable nor a_hnp_support features
If the b_hnp_enable feature is set, the B-device is allowed to do HNP, regardless of whether or not the
a_hnp_support feature is set.
If the a_hnp_support feature is set, but the b_hnp_enable feature is not set, then it is likely that
b_hnp_enable will be set later when the A-device is finished using the bus.
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If neither the b_hnp_enable or a_hnp_support features are set before the A-device puts the B-device in
a non-default configuration, then the B-device may at indicate to the user that HNP is not supported
through the current connection.
The a_hnp_support feature is only cleared on a bus reset or at the end of a session. It cannot be
cleared with a ClearFeature(a_hnp_support) command.
6.5.3
a_alt_hnp_support
Setting this feature indicates to the B-device that it is connected to an A-device port that is not capable of
HNP, but that the A-device does have an alternate port that is capable of HNP.
The A-device is required to set this feature under the following conditions:
•
•
•
the A-device has multiple receptacles
the A-device port that connects to the B-device does not support HNP
the A-device has another port that does support HNP
This feature is cleared at the end of a session. If this bit is set, and the user launches an Application that
requires the B-device to be Host, then the B-device can provide a message to the user indicating that
the user needs to connect the B-device to an alternate port on the A-device.
If both a_alt_hnp_support and a_hnp_support are set, then the meaning is the same as if only
a_alt_hnp_support was set.
If the B-device receives a SetFeature(b_hnp_enable) command when this feature is set, then HNP is
enabled in the B-device, as the b_hnp_enable bit takes precedence over the a_alt_hnp_support bit.
This feature is only cleared on a bus reset or at the end of a session. It cannot be cleared with a
ClearFeature(a_alt_hnp_support) command.
6.6
State Machine Parameters
This section describes the inputs, internal variables, timers, and outputs associated with the state
machines.
6.6.1
6.6.1.1
Inputs
a_bus_drop
The “A-device bus drop” (a_bus_drop) input is TRUE when the Application running on the A-device needs
to power down the bus, and is FALSE otherwise. When this input is TRUE, then the a_bus_req input must
be FALSE.
6.6.1.2
a_bus_req
The “A-device bus request” (a_bus_req) input is TRUE during the time that the Application running on the
A-device wants to use the bus, and is FALSE when the Application no longer wants to use the bus.
6.6.1.3
a_bus_resume
The “A-device bus resume” (a_bus_resume) variable is TRUE when the B-device detects that the Adevice is signaling a resume (i.e. K state) on the bus.
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If the B-device has transitioned to the b_wait_acon state, then a resume (i.e. K state) from the A-device
will cause the B-device to return to the b_peripheral state.
Section 7.1.7.7 of the USB 2.0 specification, states that the downstream device (in this case the Bdevice) interprets any non-idle signal as an indication that the upstream device (in this case the Adevice) is resuming operation of the bus. If the B-device is in the b_peripheral state, then this definition
for resume signaling holds.
However, if the B-device is in the b_wait_acon state, then only a J-to-K transition is treated as a
resume. After the B-device turns off its pull-up resistor the bus will be pulled to the SE0 state by the pulldowns on the A and B devices. This SE0 is not a resume indication. If the SE0 persists for more than
TB_ASE0_BRST min, then the A-device is not responding to the HNP request from the B-device and the Bdevice shall treat the SE0 on the bus as a bus reset indication. This takes the B-device back to the
b_peripheral state.
6.6.1.4
a_bus_suspend
The “A-device bus suspend” (a_bus_suspend) variable is TRUE when the B-device detects that the Adevice has put the bus into suspend.
If the B-device has been enabled to become Host (b_hnp_enable feature has been set), then the Bdevice uses this variable to transition from the b_peripheral state to the b_wait_acon state
As per Section 7.1.7.6 of the USB 2.0 specification, the downstream device (in this case the B-device)
interprets more than 3 ms of idle as an indication that the upstream device has suspended the bus.
6.6.1.5
a_conn
The “A-device connect” (a_conn) variable is used by the B-device as a condition for entering or exiting
the b_host state.
If the B-device is in the b_wait_acon state, the B-device sets a_conn TRUE if the B-device detects a
connection from the A-device. In order to detect a connection from the A-device, the B-device must
insure that there is no residual voltage on the D+ line from the B-device’s pull-up. (See Section 5.1.9).
When the B-device has qualified the high level on the D+ line as being from the A-device, and the level
has been present for at least TB_ACON_DBNC min then a_conn is set to TRUE.
Note: A dual-role device is required to operate as a full-speed peripheral. Therefore, a B-device
shall only accept a connection from an A-device when D+ is pulled up. If the B-device detects a
high on the D- line after disconnecting, this shall be interpreted as resume signaling from the Adevice.
While the B-device is in the b_host state, it will set a_conn FALSE if the B-device detects that the Adevice has disconnected, as described in Section 7.1.7.3 of the USB 2.0 specification. The B-device
also sets a_conn to FALSE whenever it goes to any state other than the b_host state.
6.6.1.6
a_sess_vld
The “A-device session valid” (a_sess_vld) input is TRUE if the A-device detects that the voltage on VBUS
is above its A-device Session Valid threshold (VA_SESS_VLD)(see Table 5-1).
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6.6.1.7
June 24, 2003
a_srp_det
The “A-device SRP detect” (a_srp_det) input is TRUE if the A-device detects SRP as defined in Section
5.3. This bit is set when either VBUS pulsing or data line pulsing is detected. This variable is set to
FALSE on initial power up of the A-device or whenever the A-device transitions to the a_wait_vfall state.
6.6.1.8
a_vbus_vld
The “A-device VBUS valid” (a_vbus_vld) input is TRUE when the VBUS voltage is above the A-device
VBUS Valid threshold. This threshold must be at or above VA_VBUS_VLD min, specified in Table 5-1.
6.6.1.9
b_bus_req
The “B-device bus request” (b_bus_req) input is TRUE during the time that the Application running on the
B-device wants to use the bus, and is FALSE when the Application no longer wants to use the bus.
6.6.1.10 b_bus_resume
The “B-device bus resume” (b_bus_resume) variable is TRUE when the A-device detects that the Bdevice is signaling a resume on the bus.
The A-device uses this variable to transition from the a_suspend state to the a_host state.
Section 7.1.7.7 of the USB 2.0 specification, states that the upstream device (in this case the A-device)
interprets any non-idle signal as an indication that the downstream device (in this case the B-device) is
waking up the bus. If the B-device is not enabled for HNP, then the behavior of the A-device in
response to bus activity from the B-device is as defined in the section cited above.
However, if the B-device is enabled for HNP, then only a J-to-K transition on the bus will be treated as a
resume. A transition to SE0 will be treated as the start of the HNP handoff. The A-device is expected to
respond by transitioning to the a_peripheral state and turning on its pull-up resistor on D+.
6.6.1.11 b_bus_suspend
The “B-device bus suspend” (b_bus_suspend) variable is TRUE when the A-device detects that the Bdevice has put the bus into suspend.
The A-device uses this variable to transition from the a_peripheral state to the a_wait_bcon state
As per Section 7.1.7.6 of the USB 2.0 specification, the downstream device (in this case the A-device)
interprets more than 3 ms of idle as an indication that the upstream device has suspended the bus.
6.6.1.12 b_conn
The “B-device connect” (b_conn) variable is used by the A-device as a condition for transitioning
between the following states:
On b_conn transition
FALSE
56
Î TRUE
Exit State
Enter State
a_wait_bcon
a_host
TRUE
Î FALSE
a_host
a_wait_bcon
TRUE
Î FALSE
a_suspend
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If b_conn is FALSE, it is set to TRUE if the B-device pulls D+ or D- high for longer than the debounce
interval. The debounce interval varies depending on how the a_wait_bcon state was entered, and how
long it has been since either D+ or D- has been pulled high. If the a_wait_bcon state was entered from
the a_peripheral, a_host or a_suspend states, then the short debounce interval (TA_BCON_SDB) is
allowed. If the a_wait_bcon state was entered from the a_wait_vrise state then the long debounce
interval (TA_BCON_LDB) is required.
The A-device is only allowed to apply the short debounce to b_conn in a window of time. If the A-device
stays in the a_wait_bcon state for longer than TA_BCON_SDB_WIN max, then the long debounce interval
applies no matter how the a_wait_bcon state was entered. Note that if the state machine is timing the
short debounce interval, changes to D- and D+ do not effect the setting of b_conn if they occur before
TLDIS_DSCHG min.
If the long debounce interval applies, then a new B-device connection is assumed and the A-device is
required to allow the B-device to become host as described in 6.8.1.4.
While the A-device is in the a_host or a_suspend state, then the A-device will set b_conn FALSE if the
A-device detects that the B-device has disconnected, as described in Section 7.1.7.3 of the USB 2.0
specification. The A-device also sets b_conn to FALSE whenever it transitions to any state other than
a_host or a_suspend.
Note: The USB 2.0 specification insures at least 100 ms from the time the device indicates a
connect until the device will be reset to start the session. This is not the case for dual-role devices.
They are not assured in all cases of a 100 ms interval after indicating a connect. When a dual-role
device signals connect, it must be prepared to receive the bus reset that starts the session.
6.6.1.13 b_se0_srp
The “B-device SE0 before SRP” (b_se0_srp) variable is TRUE when the B-device is in the b_idle state,
and the line has been at SE0 for more than the minimum time before generating SRP (TB_SE0_SRP), as
defined in Table 5-3.
6.6.1.14 b_sess_end
The “B-device session end” (b_sess_end) input is TRUE if the B-device detects that the voltage on VBUS
is below its B-Device Session End threshold (VB_SESS_END) (see Table 5-1).
6.6.1.15 b_sess_vld
The “B-device session valid” (b_sess_vld) input is TRUE when the B-device detects that the voltage on
VBUS is above its B-Device Session Valid threshold (VB_SESS_VLD)(see Table 5-1).
6.6.1.16 id
The identification (id) input is FALSE when a Mini-A plug is inserted in the device’s Mini-AB receptacle.
Otherwise, this input is TRUE.
6.6.1.17 a_suspend_req
The “A-device suspend request” (a_suspend_req) input is TRUE during the time that the Application
running on the A-device wants to suspend the bus for power savings, without ending the session. This
input is FALSE when the Application does not desire the bus to be suspended.
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6.6.2
June 24, 2003
Internal Variables
6.6.2.1
a_set_b_hnp_en
The “A-device set b_hnp_enable” (a_set_b_hnp_en) bit is TRUE when the A-device has successfully set
the b_hnp_enable bit in the B-device. The A-device sets this bit at the same time as it sets the
b_hnp_enable bit in the B-device, and clears this bit when it determines that the B-device should have
cleared the b_hnp_enable bit.
6.6.2.2
b_srp_done
The “B-device SRP done” (b_srp_done) bit is TRUE when the B-device has completed initiating SRP.
6.6.2.3
b_hnp_enable
This is the feature defined in Section 6.5.1.
6.6.3
Outputs
6.6.3.1
chrg_vbus
The “charge VBUS” (chrg_vbus) signal is TRUE when a B-device is charging VBUS through a resistor. See
Section 5.3.5.
6.6.3.2
drv_vbus
The “drive VBUS” (drv_vbus) signal is TRUE when an A-device is driving VBUS.
6.6.3.3
loc_conn
The “local connect” (loc_conn) variable is TRUE when the local device has signaled that it is connected to
the bus. This variable is FALSE when the local device has signaled that it is disconnected from the bus.
See Section 6.6.1.4.
6.6.3.4
loc_sof
The “local SOF” (loc_sof) bit is TRUE when the local device is generating activity on the bus. Activity
begins with a bus reset followed by start of frame packets (SOF’s) or low-speed keep-alives or any other
bus activity that occurs with enough frequency to prevent the Peripheral device from sensing a lack of
bus activity.
6.6.4
Informative Variables
The following variables are representations of behavior that is internal to the device.
•
•
•
•
•
a_bus_req
a_bus_drop
a_clr_err
a_suspend_req
b_bus_req
While the device must demonstrate behavior related to these variables (i.e. the A-device must turn on
VBUS in response to some activity, corresponding to receiving an a_bus_req) the actual implementation
and use of these variables is at the designer’s discretion. The inclusion of these variables within the
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following state machines is not meant to convey required operation, but is an informative example only
to show the behavior of the system.
6.6.5
Timers
The HNP state machines make use of the following timers:
Table 6-4. Dual-Role Device Timers
Timer
Timeout Time
Timeout Indication
Associated State
a_wait_vrise_tmr
TA_WAIT_VRISE
a_wait_vrise_tmout
a_wait_vrise
a_wait_bcon_tmr
TA_WAIT_BCON
a_wait_bcon_tmout
a_wait_bcon
a_aidl_bdis_tmr
TA_AIDL_BDIS
a_aidl_bdis_tmout
a_suspend
b_ase0_brst_tmr
TB_ASE0_BRST
b_ase0_brst_tmout
b_wait_acon
All timers are started on entry to and reset on exit from their associated states.
6.6.5.1
a_wait_vrise_tmr
This timer is used by an A-device in the a_wait_vrise state to wait for the voltage on VBUS to rise above
the A-device VBUS Valid threshold (a_vbus_vld = TRUE). If VBUS is not above this threshold before and
after TA_WAIT_VRISE (a_wait_vrise_tmout = TRUE), then this is an indication that the B-device is drawing
too much current.
6.6.5.2
a_wait_bcon_tmr
This timer is used by an A-device in the a_wait_bcon state, to wait for the B-device to signal a
connection, (b_conn = TRUE). If the B-device does not connect before TA_WAIT_BCON,
(a_wait_bcon_tmout = TRUE), then the A-device is allowed to stop waiting for a connection.
6.6.5.3
a_aidl_bdis_tmr
This timer is started by an A-device when it enters the a_suspend state. If the A-device does not detect
a disconnect before TA_AIDL_BDIS (a_aidl_bdis_tmout = TRUE), then the A-device is allowed to stop
waiting for a disconnect and end the session.
6.6.5.4
b_ase0_brst_tmr
This timer is used by a B-device in the b_wait_acon state, to wait for an A-device to signal a
connection, (a_conn = TRUE). If the A-device does not connect before TB_ASE0_BRST
(b_ase0_brst_tmout = TRUE), then the B-device shall assume that the A-device is signaling a bus reset
and return to the b_peripheral state.
6.6.6
Test Device Support
A device with VID=6666 (0x1A0A), PID=47837 (0xBADD) is defined to be a test device, part of the
compliance test configuration. A dual-role A-device or B-device shall treat a device with this
identification as an unsupported device, and shall interact with the test device as defined in 6.8.1.4 and
6.8.2.5 when such a device is attached.
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6.7
June 24, 2003
Timing Summary
6.7.1
B-device becoming Host
When a dual-role B-device has received a SetFeature(b_hnp_enable) and requires the bus, it must wait
for the bus enter the Suspend state before signaling a disconnect to start HNP.
After the bus enters the Suspend state, the B-device will transition from the b_peripheral to
b_wait_acon states and wait for the A-device to indicate a connect event, which would complete the
transfer of control to the B-device. While waiting in the b_wait_acon state, the B-device may detect a K
state on the bus. This indicates that the A-device is signaling a resume condition and is retaining control
of the bus. In this case, the B-device will return to the b_peripheral state.
If the B-device has had its D+ pull-up turned off for more than TLDIS_DSCHG min and a J is detected on
the bus, then this is an indication that the A-device is acknowledging the HNP request and has become
the Peripheral.
If the B-device at any time detects more than TB_ASE0_BRST min of SE0, then this is an indication that the
A-device is remaining Host and is resetting the bus, as per Section 7.1.7.5 of the USB 2.0 specification.
In this case the B-device shall return to the b_peripheral state and start to process the bus reset before
TB_ASE0_BRST max.
If the A-device turns on its pull up before TB_ASE0_BRST min of the B-device disconnecting, then the Bdevice has until TB_ACON_BSE0 max to start bus activity by issuing a bus reset.
6.7.2
A-device becoming Peripheral
When the A-device is in the a_host state and has set the dual-role B-device’s HNP enable bit
(b_hnp_enable = TRUE) the A-device shall place the connection to the B-device into Suspend when it is
finished using the bus. If the B-device disconnects after the bus has been suspended, then this is an
indication that the B-device is attempting to become Host. When the A-device detects the disconnect
from the B-device, it shall turn on its D+ pull-up resistor within 3 ms (TA_BDIS_ACON max) to acknowledge
the request from the B-device. The time in which the A-device must detect the disconnect is defined in
Table 7-13 of the USB 2.0 specification.
After the A-device signals a connect, it must continue to signal a connect for at least TA_BIDL_ADIS min,
while waiting for the B-device to issue a bus reset. This ensures that the B-device has at least
TB_ACON_BSE0 max to detect and respond to the A-device connect.
In some implementations of an A-device, the host controller may be on one chip, while the transceiver
may be on another chip. The transceiver would typically have an integrated pull up resistor, that would
be controlled by the host controller through a slow serial interface. In such an implementation, it may not
be possible for the A-device host controller to detect the B-device disconnect, and then turn on the Adevice’s pull-up resistor through the slow serial interface before TA_BDIS_ACON max. One method for
accomplishing this with the above architecture is as follows.
After finishing data transfers between the A-device and B-device, and before suspending the bus, the Adevice is sending out SOF’s. The B-device receives these SOF’s, and does not transmit any packets
back to the A-device. During this time, the A-device host controller enables a logic block in the
transceiver to look for an SE0 anytime that the A-device is not transmitting. After this logic is enabled,
the A-device stops transmitting SOF’s and allows the bus to go idle. If the B-device disconnects, then
the bus goes to SE0, and the transceiver logic automatically turns on the A-device pull up.
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Regardless of the implementation, the A-device must allow the B-device to disconnect before the Adevice connects. This is so that the A-device can detect the B-device disconnect, and transition out of
the a_suspend state.
6.8
State Diagrams
The HNP state machines are contained in this section. Figure 6-2 shows the state machine of a dualrole A-device. Figure 6-3 shows the state machine of a dual-role B-device. The HNP state machine for
a dual-role device is equivalent to the A-device state machine combined with the dual-role B-device
state machine.
An additional state diagram for an SRP capable Peripheral-only B-device is shown in Figure 6-4.
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6.8.1
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Dual-role A-Device
START
b_idle
id
drv_vbus/
chrg_vbus/
loc_conn/
loc_sof/
a_bus_drop/ &
(a_bus_req |
a_srp_det )
a_idle
id | a_bus_req |
(a_sess_vld/ &
b_conn/)
drv_vbus/
chrg_vbus/
loc_conn/
loc_sof/
a_wait_vfall
drv_vbus/
loc_conn/
loc_sof/
a_wait_vrise
id | a_bus_drop |
a_wait_bcon_tmout
id | a_bus_drop |
a_clr_err
id | a_bus_drop |
a_vbus_vld |
a_wait_vrise_tmout
b_bus_suspend
id |
a_bus_drop
drv_vbus
loc_conn/
loc_sof/
a_vbus_err
a_peripheral
a_vbus_vld/
drv_vbus
loc_conn
loc_sof/
id |
a_bus_drop |
a_aidl_bdis_tmout
drv_vbus/
loc_conn/
loc_sof/
a_vbus_vld/
a_vbus_vld/
a_vbus_vld/
a_suspend
a_bus_req |
b_bus_resume
a_bus_req/ |
a_suspend_req
Figure 6-2 Dual-Role A-device State Diagram
62
drv_vbus
loc_conn/
loc_sof/
b_conn/ &
a_set_b_hnp_en
b_conn/ &
a_set_b_hnp_en/
drv_vbus
loc_conn/
loc_sof/
a_wait_bcon
id |
b_conn/ |
a_bus_drop
a_host
drv_vbus
loc_conn/
loc_sof
b_conn
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The A-device state diagram shown in Figure 6-2 consists of the following eight states:
•
•
•
•
•
•
•
•
a_idle
a_wait_vrise
a_wait_bcon
a_host
a_suspend
a_peripheral
a_wait_vfall
a_vbus_err
There is a transition to the dual-role B-device start state (b_idle) that occurs if the cable is disconnected.
When the A-Device is in any state except the a_idle state, the A-Device transitions to the a_wait_vfall
state before transitioning to the a_idle state and then to the b_idle state.
6.8.1.1
a_idle
This is the start state for A-devices.
The A-device transitions to the a_wait_vrise state:
•
•
•
6.8.1.2
if the A-device application is not wanting to drop the bus (a_bus_drop = FALSE), and
if the A-device Application is requesting the bus (a_bus_req = TRUE), or
SRP is detected on the bus (a_srp_det = TRUE).
a_wait_vrise
In this state, the A-device waits for the voltage on VBUS to rise above the A-Device VBUS Valid threshold
(a_vbus_vld = TRUE). Upon entering this state, the A-device starts a timer: a_wait_vrise_tmr.
The A-device transitions to the a_wait_bcon state:
•
•
6.8.1.3
if the voltage on VBUS has risen above the A-device VBUS Valid threshold (a_vbus_vld = TRUE),
or
if the a_wait_vrise_tmr expires.
a_wait_bcon
In this state, the A-device waits for the B-device to signal a connection. Upon entering this state, the Adevice starts a timer: a_wait_bcon_tmr.
The A-device transitions to the a_wait_vfall state:
•
•
•
if the cable is removed (id = TRUE), or
if the A-device Application wants to drop the bus (a_bus_drop = TRUE), or
if the a_wait_bcon_tmr times out (a_wait_bcon_tmout = TRUE).
If VBUS drops below the A-device VBUS Valid threshold (a_vbus_vld = FALSE), then the A-device
transitions to the a_vbus_err state.
If the A-device detects the B-device signaling a connection (b_conn = TRUE), then the A-device shall end
the session or transition to the a_host state and generate a bus reset within TA_BCON_ARST. See
Section 6.6.1.12 for information on b_conn.
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Note: a device may set its a_wait_bcon_tmr to an arbitrarily large value and wait an indefinitely long
period of time for the B-device to connect.
6.8.1.4
a_host
Upon entering this state, the A-device resets the bus to prepare the B-device for packet traffic.
If a_bus_req = TRUE, then the A-device application wants to communicate with the B-device, and the Adevice performs the following actions:
•
•
•
•
A-device enumerates B-device
if A-device supports B-device (i.e. B-device is on Targeted Peripheral List), then A-device sets
up communication with B-device
else if A-device does not support B-device then A-device outputs message to user indicating
that B-device is not supported
A-device sets a_bus_req = FALSE
Before ending the session, the A-device must allow a dual-role B-device the opportunity to take control
of the bus. To do this, the A-device sends a SetFeature(b_hnp_enable) command. The A-device may
send the SetFeature(b_hnp_enable) command to any B-device but is only required to send the
command if the B-device is HNP capable (indicated in the OTG Descriptor). If the B-device responds to
the SetFeature(B_hnp_enable) with a STALL, then the B-device is not HNP capable. If the SetFeature
command is accepted, then the A-device shall exit to the a_suspend state and wait for the B-device to
start the HNP. The A-device is allowed to transition to the a_suspend state without setting
b_hnp_enable, if it does not want the B-device to become Host but wants to continue to power the bus
(possibly in expectation of imminent user input). If it does suspend the bus without enabling HNP, then it
must at some later time return to this state and enable HNP if the B-device is dual-role.
The dual-role A-device is required to perform HNP within TA_SRP_RSPNS max if it enumerates the Bdevice and discovers that the test device (defined in section 6.6.6) is attached. The dual-role A-device is
not required to display an unsupported device message when attached to the test device. If the dualrole A-device does display an unsupported device message, the message shall not delay HNP. When
connected to a test device, an A-device is not allowed to drive a resume signal longer than 30 seconds.
If an A-device has already granted the role of host to the test device once during a session, then the Adevice is not required to grant the role of host to test device again during the same session.
Under the following conditions, the A-device transitions from the a_host state to the a_wait_bcon state:
•
•
•
if the cable is removed (id = TRUE), or
if the A-device wishes to stop powering VBUS (bus_drop = TRUE), or
if the B-device disconnects (b_conn = FALSE).
If VBUS is or drops below the VBUS Valid value (a_vbus_vld = FALSE), then the A-device transitions to the
a_vbus_err state.
6.8.1.5
a_suspend
Upon entering the a_suspend state, the A-device starts the a_aidl_bdis_tmr. This timer can be set to
an arbitrarily long time, but must be longer than TA_AIDL_BDIS min.
The A-device transitions to the a_wait_vfall state:
•
64
if the a_aidl_bdis_tmr times out (a_aidl_bdis_tmout = TRUE), or
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•
•
June 24, 2003
if the A-device wishes to stop powering VBUS (bus_drop = TRUE) , or
if the the cable is removed (id = TRUE).
If the B-device signals a disconnect (b_conn = FALSE), and the A-device was successful in setting
b_hnp_enable (a_set_b_hnp_en = TRUE), then the A-device transitions to the a_peripheral state.
The A-device transitions to the a_host state if either a_bus_req is asserted, or if the B-device signals a
resume by putting a K state on the bus, even if the remote_wakeup feature has not been enabled. If
a_bus_req is asserted, then the A-device can either do a resume by putting a K state on the bus, or it
can do a bus reset by outputting SE0 for longer than TB_ASE0_BRST max. The dual-role A-device is not
allowed to resume unless the attached device is supported, or until TAIDL_BDIS max time has elapsed.
If the B-device signals a disconnect (b_conn = FALSE), and the A-device did not set b_hnp_enable
(a_set_b_hnp_en = FALSE), then the A-device transitions to the a_wait_bcon state.
If VBUS is or drops below the A-device VBUS Valid value (a_vbus_vld = FALSE), then the A-device
transitions to the a_vbus_err state.
6.8.1.6
a_peripheral
In this state, the A-device signals a connection to the B-device (loc conn = TRUE) and responds to
requests from the dual-role B-device. If the A-device is capable of HS operation, then it shall begin the
high-speed detection handshake whenever a bus reset is detected.
The A-device transitions from the a_peripheral state to the a_wait_vfall state:
•
•
if the cable is removed (id = TRUE), or
if the A-device is no longer capable of powering VBUS (bus_drop = TRUE).
If the A-device detects more than TA_BIDL_ADIS min of continuous idle (i.e. J_state for full-speed or SE0
for high-speed), on the bus, then the A-device may transition to the a_wait_bcon state. If no activity is
detected after TA_ BIDL_ADIS max the A-device must transition back to the a_wait_bcon state.
If VBUS is or drops below the A-device VBUS Valid threshold (a_vbus_vld = FALSE), then the A-device
transitions to the a_vbus_err state.
This is the only state in which the A-device will signal a connection to the B-device.
6.8.1.7
a_wait_vfall
In this state, the A-device waits for the voltage on VBUS to drop below the A-device Session Valid
threshold (a_sess_vld = FALSE) and for the B-device to drop D+/D- to indicate that it has detected the
end of the session. Once both of these conditions are met, then the A-device transitions to the a_idle
state. If the A-device is not dual-role and does not respond to the VBUS pulsing SRP, then the A-device
transitions to a_idle when the bus enters the SE0 state and does not wait for VBUS to fall below the
Va_sess_vld, threshold.
6.8.1.8
a_vbus_err
In this state, the A-device waits for recovery of the overcurrent condition that caused it to enter this state.
Upon assertion of a_clr_err (nominally by system software), the A-device transitions to the a_wait_vfall
state.
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6.8.2
June 24, 2003
Dual-Role B-Device
a_idle
id/
START
drv_vbus/
chrg_vbus/
loc_conn/
loc_sof/
b_idle
id/ |
b_sess_vld/
b_host
chrg_vbus/
loc_conn/
loc_sof
drv_vbus/
chrg_vbus/
loc_conn/
loc_sof/
b_bus_req &
b_sess_end &
b_se0_srp
id/ |
b_sess_vld/
id/ |
b_sess_vld/
b_bus_req/ |
a_conn/
a_conn
id/ |
b_srp_done
b_sess_vld
b_srp_init
pulse loc_conn
pulse chrg_vbus
loc_sof/
a_bus_resume |
b_ase0_brst_tmout
b_wait_acon
b_peripheral
chrg_vbus/
loc_conn/
loc_sof/
chrg_vbus/
loc_conn
loc_sof/
b_bus_req &
b_hnp_en &
a_bus_suspend
Figure 6-3 Dual-Role B-device State Diagram
The dual-role B-device state diagram consists of five distinct states:
•
•
•
•
•
6.8.2.1
b_idle
b_srp_init
b_peripheral
b_wait_acon
b_host
b_idle
In this state, the dual-role B-device waits for a session to start by monitoring if VBUS rises above the BDevice Session Valid threshold (b_sess_vld = TRUE). If VBUS rises above this threshold, the dual-role Bdevice enters the b_peripheral state and signals a connect (loc_conn = TRUE).
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June 24, 2003
The B-device transitions from the b_idle to the b_srp_init state:
•
•
•
if the Application indicates that it wants to start a session (b_bus_req = TRUE), and
if VBUS is below the B-device Session End threshold (b_sess_end = TRUE), and
if the bus has been in the SE0 state for at least TB_SE0_SRP min.
If the Mini-A plug is inserted (id = FALSE), then the dual-role B-device transitions to the a_idle state and
becomes an A-device.
6.8.2.2
b_srp_init
Upon entering this state, the dual-role B-device attempts to initiate a session via SRP. Upon completion,
the dual-role B-device returns to the b_idle state, nominally to wait for the A-device to drive VBUS above
the B-Device Session Valid threshold (b_sess_vld = TRUE). Since the B-Device cannot distinguish
between the A-device driving Vbus high, and any residual effect of the B-device signaling SRP on Vbus,
the B-device must assume that Vbus above the B-device session threshold is due to A-device driving it
high.
The B-device is required to complete its SRP activities in less than TB_SRP_INIT max. On entry to this
state, the B-device shall provide an indication to the user that it is trying to establish communications
with the A-device and a timer is started. This timer will continue to run until the B-device enters the
b_peripheral state. If the timer reaches a vendor specific limit between TB_SRP_FAIL min and
TB_SRP_FAIL max the B-device will indicate to the user that the A-device did not respond.
6.8.2.3
b_peripheral
In this state, the dual-role B-device acts as the peripheral, and responds to requests from the A-device.
If the dual-role B-device wishes to assume the role of Host (b_bus_req = TRUE) and the A-device has
granted the dual-role B-device permission (b_hnp_enable = TRUE) and the bus is in the Suspend state,
then the dual-role B-device transitions to the b_wait_acon state. In the event that the dual-role Bdevice started the session with an SRP request, the dual-role B-device shall transition to the
b_wait_acon state within the TA_AIDL_BDIS timeout, even if there is no longer an outstanding
bus_request.
If a Mini-A plug is inserted (id = FALSE) or if VBUS drops below the B-device Session Valid threshold
(b_sess_vld = FALSE), then the dual-role B-device transitions to the b_idle state.
When a high-speed capable B-device enters this state it shall enable its pull-up on D+. After the Bdevice enables its pull-up, it must monitor the state of the bus to determine if a bus reset is being
signaled by the A-device. If the pull-up is turned on for TWTRSTHS (Table 7-14 in USB 2.0 specification)
and the bus is in the SE0 state then a reset condition exists. (Note: The TWRTSTHS is a sample point that
occurs at a device dependent time after the pull-up resistor is turned on.) If the B-device is capable of
HS, it shall begin the high-speed detection handshake any time that a bus reset condition exists.
6.8.2.4
b_wait_acon
In this state, the dual-role B-device has received a SetFeature(b_hnp_enable) giving it permission to
assume the role of Host and it has detected that the bus has gone to the Suspend state. Upon entering
this state, the dual-role B-device turns off its pull-up resistor on D+, starts a timer (b_ase0_brst_tmr), and
waits for the A-device to signal a connect.
The dual-role B-device returns to the b_peripheral state:
•
if the b_ase0_brst_tmr expires (b_ase0_brst_tmout = TRUE), or
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•
June 24, 2003
if the B-device detects a K_state on the bus, indicating that the A-device is signaling a resume
(a_bus_resume = TRUE)
If the A-device signals a connect (a_conn = TRUE) before the b_ase0_brst_tmr expires, then the Bdevice transitions to the b_host state. The B-device shall be able to detect the connect from the Adevice and transition to the b_host state within TB_ACON_BSE0 max after D+ is detected to be high at the
B-device.
If a Mini-A plug is inserted (id = FALSE) or VBUS drops below the session valid threshold (b_sess_vld =
FALSE), then the dual-role B-device transitions to the b_idle state.
6.8.2.5
b_host
Upon entering this state, the B-device issues a bus reset, and starts generating SOF’s. The B-device
may query the A-device for its descriptors.
While the B-device is in this state, the A-device responds to requests from the B-device. If the B-device
does not support the A-device, then the B-device shall provide a message to the user informing them of
this.
Once the B-device has completed its usage of the A-device (b_bus_req = FALSE), or if the B-device
detects that the A-device has signaled a disconnect (a_conn = FALSE), or within 30 seconds of the dualrole B-device detecting that the test device (defined in section 6.6.6) is attached, then the B-device stops
generating bus activity (loc_sof = FALSE) and transitions to the b_peripheral state.
If a Mini-A plug is inserted (id = FALSE) or VBUS drops below the B-device Session Valid threshold
(b_sess_vld = FALSE), then the dual-role B-device transitions to the b_idle state.
6.8.3
Peripheral-Only, B-Device
START
b_idle
b_sess_vld/
b_peripheral
chrg_vbus/
loc_conn
b_sess_req &
b_sess_end &
a_bus_low
chrg_vbus/
loc_conn/
b_sess_vld
b_srp_done
b_srp_init
pulse loc_conn
pulse chrg_vbus
Figure 6-4 SRP Capable Peripheral-Only B-device State Diagram
The state diagram is only relevant for SRP capable Peripheral-only B-device. It consists of three distinct
states:
•
•
•
68
b_idle
b_srp_init
b_peripheral
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6.8.3.1
June 24, 2003
b_idle
In this state, the Peripheral-only B-device waits for a session to start by monitoring if VBUS rises above
the B-device VBUS Session Threshold (VB_SESS_VLD). If VBUS rises above this threshold, the Peripheralonly B-device enters the b_peripheral state.
The B-device transitions from the b_idle state to the b_srp_init state:
•
•
•
6.8.3.2
if the Application indicates that it wants to start a session (bus_req = TRUE), and
if VBUS is below the B-device Session End threshold (b_sess_end = TRUE), and
if the bus has been in the SE0 state for at least TB_SE0_SRP min.
b_srp_init
Upon entering this state, the device attempts to start a session using the SRP defined in Section 5.3.
Upon completion, the device returns to the b_idle state.
6.8.3.3
b_peripheral
In this state, the B-device acts as a normal, USB 2.0 compliant device.
If VBUS drops below the B-device Session Valid threshold (b_sess_vld = FALSE), then the device
transitions to the b_idle state.
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