Universal Serial Bus

USB Interface


[USB Description]
[USB Interface ICs]
[USB Pinout] [USB Connector]
[USB Standard / Organizations]
[USB Converter, Adapter, Cables]
[Home]

USB Description

The USB [Universal Serial Bus] spec defines the Mechanical, Electrical and Protocol layers of the interface. Cables and connectors are fully defined. USB defines 2 types of hardware, Hubs and Functions. Up to 127 devices may be connected together in a tiered Star topology [Bus Topologies]. The limiting factor being 7 address bits. The physical wire segments are point-to-point between a Host, Hub, or Function. The system may only have one Host, which connects to a Hub. A USB Hub may connect to another Hub or to a USB Function. Each layer transition from Hub to Hub represents another Tier. USB Hubs allow connection to a USB bus, while USB Functions are the devices which perform some function.

The USB bus is a [Differential] Bi-directional serial interface cable bus. Differential NRZI data is transmitted Isochronous or Asynchronous between devices. Data is transferred at three different rates over a maximum cable length of 4 meters ~ over 4 wires, 2 of which carry data on a balanced twisted pair.
USB may operate at any speed from 10kbps to 400Mbps in one of three speed modes. A Slow-Speed mode of 10kbps to 100kbps is used for devices such as a USB keyboard or USB mouse. Full-Speed mode is used by most devices and allows a transfer rate of 500kbps to 10Mbps. High-Speed mode [defined by USB 2.0] allows rates of up to 480Mbps, with a speed range of 25Mbps to 400Mbps. Transmission at the High-Speed mode requires the addition of 45 ohm termination resistors between each data line and ground. Operation at Full-Speed mode is 2.8 volts [High] to 0.3 volts [Low]. Operation at High-Speed mode is at 400mV +/-10% [High] to 0V +/- 10mV {Low]. Cable impedance for both modes is 90 ohms +/- 15% (differential).

Four different (packet) protocols are used; Control, Interrupt, Isochronous and Bulk. Each exchange contains 3 packets; A token packet which holds the address, a data packet which holds the data, and a handshake packet which terminate the exchange.
NRZI produces a change in the signal indicating a logic zero, no change indicates a logic one. Bit stuffing is used with NRZI to stop the signal remaining in the steady state condition; if more then 6 ones are transmitted (no change in the signal) a zero is inserted to produce a transition. NRZI, with bit stuffing is self clocking, allowing the receiver to synchronize with the transmitter.

USB 3.0 (Super-Speed USB) increases the data rate to 4.8 Gbit/s, 600 MB/s. USB 3.0 ports and cabling are designed to enable backward compatibility, so the new connector and cable contains both a USB 3.0 interface and a USB 2.0 interface.
USB 3.0 connectors contain legacy pins to interface to USB 2.0 devices, and a new set of pins for USB 3.0 connectivity (both sets reside in the same connector).
Editor note; when the new standard was first announced USB 3.0 would be adding a fiber interface; 'future-proofing for optical capabilities'. However; the final standard used a PCIe 'like' interface to add USB 3.0 capabilities.

{USB Bus Index}


USB Standard and Specifications

The Universal Serial Bus specification was first released in 1994. The current USB standard, Revision 2.0 was released in 2000.
Revision 3.0 (Superspeed USB) was released in 2008.

USB 2.0 Specification {USB.org}
Provides both version 2.0 and version 1.1 of the USB Standard

micro-USB Description {micro-USB description and devices}

Enhanced Host Controller Interface [EHCI] specification describes the register-level interface for a Host Controller for the Universal Serial Bus (USB) Revision 2.0

Wireless USB description and details. USB w/ wireless access

There are two different IC USB standards; HSIC, and Inter-IC USB

VoIP Phone Manufacturers {USB Voice of IP devices}

ReadyBoost, which is a blog post.

{USB Bus top}


USB Bus Interface IC Manufacturers

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Atmel {USB Hub Manufacturer}

Cypress {USB IC Manufacturer, USB 1.0/2/0, USB On-The-Go 'OTG'}

Epson {USB20 Device Controllers}

Exar {USB Vbus Switches}

Fairchild Semiconductor, Corp. {Universal Serial Bus Transceiver, USB 2.0 FS Peripheral Transceiver, Dual Port Hi-Speed USB 2.0, USB Switch Dual SPDT Multiplexer/Demultiplexer}

Freescale Semiconductor, Inc. {USB Controller IC Manufacturer}

FTDI Future Technology Devices International Limited {USB UART-Controller / USB Hub Controller}

Genesyslogic company {USB 2.0 Host Controller, USB 2.0 Flash Drive Controller, USB 2.0 Card Reader Controller}

initio Corp. {USB 2.0/1394a Bridge Controller; 400/800Mbit}

Intel {USB Controllers}

LSI Corporation {USB Core: Hub, Host, Controller}

Lucent Technologies {USB to Parallel-USB Controller-PCI to USB Host Controller IC}

Micrel Semiconductor {USB Integrated Circuit Manufacturer}

National Semiconductor {USB Controller IC}

NXP {ULPI Transceivers, USB On-The-Go (OTG) Controllers, USB Hub Controllers, USB Host Controllers, USB Peripheral controllers, USB Transceivers}

PLX Technology {USB Device Controller}

Standard Microsystems Corp. 'SMSC' {USB2.0 ATA/ATAPI Controller, Floppy Disk Controller, Flash Media Controller}

STMicroelectronics {USB Controller ICs}

TI {USB IC Manufacturer}

IC Manufacturers {All other types}

{USB Interface Bus Index}


USB Pinout

USB Type A Molded Connector Cable End
USB Type A Connector
USB Type B Molded Connector Cable End
USB Type B Connector


The USB pinout is the same for either a type A or B connector.
The difference is in the shape of the connector not the pinout.

USB Pinout, Cable Assembly
Pin Signal Name Description
1 VBUS Red
2 D- White
3 D+ Green
4 GND Black
Shell Shield Drain

USB Type A Connector pinout
USB Pin Location, Type A Connector

{USB Interface Bus top}


USB Connector Manufacturers

Stacked USB Type A Connector pinout
USB Type A, Stacked

(Type A/B, Male/Female)

Four different types: the (A/B) Jacks are used on the chassis side, and the (A/B) Plugs are used on the cable ends.
Type A jacks [female] connect to type A plugs [male], and type B jacks connect to type B plugs.
Normally Hubs will have an A jack. Cables will have an A plug on one end an a B plug on the opposite end.
The connectors have both pins 1 and 4 longer then 2 and 3, so power and ground mate first.
Having the power and ground pins mate first allow devices to be Hot-Swappable.
Type A connectors point to the Hub, while type B connectors point to the Function.
Normally a cable will have a type A connector on the computer side [Hub] and a USB type B connector on the far [function] side, to a USB device.
The cable pinout and signal names are shown in the table above [90 ohms +/-15% differential impedance]


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micro-USB Connector Manufacturers

ACON {USB plugs and receptacles SMT and Thru-hole. Mini USB 5Pin(one ID Pin), 0.8mm pitch, super mini connector}

Amphenol {Board/Cable Mount Receptacles}

Cypress Industries {USB Connector Manufacturer}

FCI {USB Connectors}

Keystone {USB Type A/B Sockets, USB Type A/B Plug}

Kycon {USB Connectors}

ITT Cannon {USB Series A/B Connectors, USB Cable Plug Assemblies}

Molex {USB Connector Manufacturer}

Newnex Technology Corp. {USB Connectors-Cable Assemblies}

OUPIIN America Inc. {Type A, B USB Connectors}

Panasonic Electric Works {USB Series A - B connectors}

Power Dynamics {USB Type A Connector Manufacturer}

Samtec {USB-B, USBR-B, USB-A, USBR-A (USB Receptacles), USB-AM (USB Plug), MUSB (Mini USB Receptacle)}

Switchcraft {Single/dual USB connectors}

Tyco Electronics {USB Connectors}

Types of USB Connectors, revision 2.0
USB Connector Styles

{USB top}


USB Cable Assemblies and Adaptors

USB Bus Cable Drawing Cut-Away
USB Cable Layout

Cable is 4 wire. The data wires are 28 AWG, the power wires are 20 to 28 AWG.
Two power lines are un-twisted and 2 data lines, twisted. Longer cables will use 20 AWG for power.
The wire are color coded per the drawing above. Cables will have an A plug on one end an a B plug on the opposite end.
The maximum cable length is 5 meters; however that can be increased by using Hubs. The USB interface is designed to operate down to -20 degrees C.

RAM Electronics Industries Inc {USB Converters / USB Adaptors / USB Cable Assemblies}
icron {Extreme USB - USB Converter, Hub/Hub allows USB up to 100 meters}
The USB pinout is shown above.

Possible transition cable assemblies include; USB to IEEE488, USB to GPIB, USB to RS232 and USB to RS422.


USB Software Vendors

Converters for legacy peripherals to Universal Serial Bus, Device Drivers from FTDI [www.ftdichip.com]

Device Driver Development Tool from Jungo [www.jungo.com]

{USB Interface Bus Top}


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Modified 2/29/12
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