U S B

UNIVERSAL SERIAL BUS

A modern computer system is likely to involve a wide variety of devices such as keyboards, microphones, cameras, speakers ,and display devices.

Most computers also have a wired or wireless connection to the internet.

A key requirement in such an environment is availability of simple ,low-cost mechanism to connect these devices to computer , and an important recent development in this regard is introduction of the Universal Serial Bus(USB).

TYPES

The USB supports two speeds of operation called, 1.low-speed(1.5 megabits/s) 2.full-speed(12 megabits/s)

USB 1.0(January 1996)

(USB 2.0) high-speed 1999 -(480 megabits/s)

(USB 3.0) super-speedsep 2007 -(3.2 Gbits/s)

OBJECTIVES:

1.USB is a simple, low-cost, speedy and expandable connection .

2.It overcomes the limited number of I/O ports available on a computer.

3.Accommodate a wide range of data transfer characteristics for I/O devices, including telephone and internet connection.

4.Plug-and-play

PORT LIMITATION

To add a new ports, a user must open the computer box to gain access to the internal expansion bus and install a new interface card.

An objective of the USB is to make it possible to add many devices to a computer system at any time , without opening the computer box.

DEVICE CHARACTERISTICS

The speed, volume, and timing constrains associated with data transfers to and from such devices vary significantly.

PLUG-AND-PLAY

The plug-and-play feature means that a new device ,such as an additional speaker can be connected any time while the system is operating.

The system should detect the existence of this new device automatically, identify the appropriate device driver software and other facilities needed to service to that device, that also establish automatically.

USB ARCHITECTURE

USB PROTOCOL

All information transferred over the USB is organized in packets.

Packet consists of one or more bytes of information.

Categories: 1.Control packets(Token packets) -it perform such task as addressing

a device to initiate data transfer. 2.Data packets -it carry information that is

delivered to a device.

Packet identifier field

Token packet, IN or OUT (CRC-Cycle Redundancy Check)

Data packet

A OUTPUT TRANSFER

ADVANTAGES:

a) Easy to use b) Accomodate wide range of I/O devices,

including connection of PC to telephone. c) Port expansion (upto 127 devices) d) low cost e) User convenience plug and play (pnp)

QUESTIONS…