Universal Serial Bus Specification Revision 2.0

Universal Serial Bus Specification Revision 2.0

Chapter 2

Terms and Abbreviations





Active Device


Asynchronous Data


Asynchronous RA



Asynchronous SRC



Audio Device












Big Endian






Bit Stuffing














Bulk Transfer



Bus Enumeration











Configuring Software



Control Endpoint


Control Pipe


Control Transfer



Computer Telephony Integration (CTI)


Cyclic Redundancy

Check (CRC)


Default Address


Default Pipe





Device Address


Device Endpoint



Device Resources



Device Software





Driver (hardware)


Driver (software)


DWORD (Double Word)


Dynamic Insertion

and Removal





Read Only Memory



End User




Endpoint Address


Endpoint Direction


Endpoint Number


Envelope detector







External Port


Eye pattern



False EOP





Frame Pattern











Handshake Packet









Host Controller


Host Controller

Driver (HCD)


Host Resources




Hub Tier



Interrupt Request



Interrupt Transfer



I/O Request Packet







Isochronous Data



Isochronous Device



Isochronous Sink



Isochronous Source












Little Endian















Message Pipe










Non Return to Zero

Invert (NRZI)








Packet Buffer


Packet ID (PID)





Phase Locked Loop



Physical Device














Power On Reset




Data Rate







Rate Adaption







Root Hub


Root Port




Sample Rate (Fs)


Sample Rate

Conversion (SRC)




Service Interval


Service Jitter


Service Rate








Split transaction









Stream Pipe





Synchronous RA



Synchronous SRC





Interface (SPI)










Time Division




Time Domain






Token Packet











Transfer Type


Turn-around Time


Universal Serial

Bus Driver (USBD)


Universal Serial

Bus Resources






USB-IF (USB Implementers Forum Inc.)


Virtual Device



A signal passed between communicating processes to signify acknowledgement of a response.


A device that is powered or currently in use.


Data transferred at random intervals between devices.


The incoming and outgoing data rate of the Rate Adaption process

are both independent. See Rate Adaption.

A device that is represented by a software interface layer.

The incoming and outgoing sample rate of the Sample Rate Conversion

process are both independent. See Sample Rate Conversion.


A device that sources sampled continuous signals for which the time varying feature of the signal is a representation of some other time varying quantity.


The measurement of an electrical wire’s diameter.


The presence of bus activity past the end of a frame with the potential to either deadlock the bus or force out the beginning of the next frame.


A measurement comparing the amount of data transmitted against a given unit of time. Typically Bandwidth is calculated as either bits per second (b/s) or bytes per second (B/s).


A method of storing data that places the most significant byte at a lower storage address.


A unit of digital information. Expresses the choice between

two possibilities represented by a logical one (1) or zero (0).


Insertion of a zero (0) bit into a given stream of data to cause an electrical transition on the data wires, allowing a phase-locked loop control system to remain locked.


The rate at which information is processed by a transmission expressed in bits per second.


The rate at which information is processed by a transmission expressed in bytes per second.



Temporary data storage used to compensate for a difference in data rates when transferring data from one device to another.


Large, irregular communication typically used for a transfer that can use any available bandwidth.


Discovering and recognizing USB devices.


Eight (8) bits.


Features of a USB device executed by the host.


Unalterable qualities of a USB device.


A user that interacts with the USB to organize a data transfer between a function and the host.


A software resident on the host software that is responsible for configuring a

USB device.


A pair of device endpoints with the same endpoint number.


See Message Pipe.


Support configuration/command/status type transmissions between client and function.


Any technology that permits interactions on a telephone and a computer to be integrated.


A check performed on data to see if an error has occurred during transmission.


An address used by a USB device when it is first powered or reset.


The message pipe created by the USB System Software to pass control and

status information between the host and a USB device’s endpoint zero.


A collection of hardware components that perform a particular function.


A 7-bit value representing the address of a device on the USB.


A uniquely addressable portion of a USB that carries data between the host computer and device in only one direction.


Resources provided by a USB device.



A collection of programs and related data that are integrated within a USB device.


The direction of data flow traveling away from the host.


An I/O pad that drives an external load.


A program responsible for interfacing to a hardware device.


A data element that is thirty-two (32) bits in size.



The ability to attach and remove devices while the host is operating.



Stable, rewritable memory.






The user of a host.


See Device Endpoint.


An endpoint number with an endpoint direction on a USB device.


The direction of data transfer on a USB.


A four (4) bit value between 0H and FH.


An electronic circuit inside a USB device that detects certain voltage related signal characteristics within the USB data lines .


End of Frame.


End of Packet.


See Port.


A USB signaling representation that provides minimum and maximum

voltage levels.


An artificial, usually noise-activated event that is decoded by a packet receiver as an EOP.


A one (1) millisecond time base.


A sequence of frames that exhibit a repeating pattern in the number of samples transmitted per frame.


See sample rate.


A computer data transmission that occurs in both directions at once.


USB operation at twelve (12) Mb/s.


A USB device that administers a capability to the host.


A packet that approves or rejects a specific condition.


A high-speed device endpoint that transfers between 1024 to 3073 bytes per microframe.


USB operation at 480 Mb/s.


The computer system where the USB Host Controller is installed.


The host’s USB interface.


The USB software layer that provides an SPI for interaction with a Host Controller while hiding the specifics of its hardware implementation.


Resources provided by a host.


A device that provides multiple USB connections.


The number of USB links in a communication path between the host

and a function plus one (1).


A hardware signal that allows a device to request support from a host.



A small, non-periodic, low-frequency, and bounded-latency USB data transfer.


A request to move data between a host and an endpoint in an appropriate direction.


See I/O Request Packet.


See Interrupt Request.


Data stream whose timing is represented by its delivery rate.



A device with isochronous endpoints that consumes and produces sampled analog streams.


An endpoint that consumes isochronous data streams that are sent by the host.



An endpoint that produces isochronous data streams and sends it to the host.



USB data transfer that provides periodic, continuous communication between a host and a device.


Lack of synchronization caused by mechanical or electrical changes.


Kilobits per second.


Kilobytes per second.


Data storage process that places the least significant byte of multiple-byte

values at lower storage addresses.


Loss of bus activity.


USB operation at 1.5 Mb/s.


Least significant bit.


Least significant byte.


Megabits per second.


Megabytes per second.


A two-way pipe that transfers data using a request/data/status pattern.


A 125 microsecond time base.


Most significant bit .


Most significant byte.


Handshake packet that displays a negative acknowledgment.


A way of encrypting serial data in which one (1) and zero (0) are represented by conflicting fluctuations of high and low voltages.


See Non Return to Zero Invert.


A data structure symbolizing a USB.


A data bundle arranged for transmission.


Buffer used by a USB for transmitting or receiving a packet.


A field in a USB packet that displays the format and the type of error detection assigned to the packet.


A token, data, or handshake packet.


A circuit that keeps an oscillator in phase with approaching frequency.



A device that has a physical embodiment .


See Packet ID.


The association between an endpoint on a device and software on the host.


See Phase Locked Loop.


Asking multiple devices if they have any data to transmit.


See Power On Reset.


Point of access to or from a system or circuit.


Restoring a storage device, register, or memory to a predetermined state when

power is applied.


A fixed data rate.



A set of rules associated with the format and timing of data transmission between two devices.


See rate adaptation.


Process by which incoming data streams are changed to outgoing data streams.


A command made to a USB contained within a SETUP packet.


To complete service for a transfer and notify the software client.


A USB hub directly attached to the Host Controller.


The downstream port on a Root Hub.


Smallest data unit on which an endpoint operates.


Number of samples per second, expressed in Hertz (Hz).


An application of the RA process used on sampled analog data streams.



A procedure provided by a System Programming Interface (SPI).


Interval between requests to an endpoint to send or receive data.


The change of service delivery from its scheduled delivery time.


Number of services to an endpoint per unit time.


See Start-of-Frame.




See System Programming Interface.


A transaction type supported by host controllers and hubs.


See Sample Rate Conversion.


A part of a sequence composing a control transfer.


The first transaction in each (micro)frame.



A pipe that transmits data as a stream of samples.


Classification that distinguishes an isochronous endpoint’s ability to connect to other isochronous endpoints.


Incoming data rates and outgoing data rates of an RA process are derived from the same master clock.


Incoming sample rates and outgoing sample rates of the SRC process are derived from the same master clock.


A defined interface to services provided by system software.





See Time Division Multiplexing.


See Time Domain Reflectometer.


Inactive components attached at the end of cables to block signals from being displayed or mirrored.


Transmitting multiple signals simultaneously by interleaving a piece of each signal one after another.



Tool capable of measuring impedance characteristics of USB signal lines.




Detection of a lack of bus activity at an interval.


Packet that identifies what transaction is to be performed on the bus.


The delivery of service to an endpoint.


A USB component that reacts to special high-speed transactions and converts them to full/low-speed transactions with full/low-speed devices attached on downstream facing ports.


Bus transactions moved between a software client and its function.



Data flow category between a software client and its function.


The time a device needs to begin communicating a packet.


Provides services to clients that are manipulating a function on a Host Controller.


Resources provided by a USB.



The direction of data flow towards the host.


See Universal Serial Bus Driver.


Nonprofit corporation formed to facilitate the development of USB compliant products and promote the technology.



A device that is represented by a software interface layer.


Data element 16 bits in size.


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Vincent Clarke

Vincent Clarke is the Universal Serial Bus (USB) Guru for USBtips.com. When he's not writing tutorials and catching up on the latest USB news, Vincent is busy preparing his next blog post and answering USB questions from his readers and subscribers.

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