USB BY

SUKESH SHETTY

Universal serial bus Wired high speed serial bus for data communication

follows star topology

Supports connection up to 127

USB is a n/w of attachments connected to host which

comes in 2 types namely “functions”& “hubs”

USB host contains host controller responsible for

controlling data communication

Different std. to implement USB host control

interface are open host control interface (OHCI) &

Universal host control interface(UHCI).

Transmits data in packet form having standard

format

Each USB data transfer consists of

- Token packet (header defining what it wants

to follow)

- Optional data packet (contains the payload)

- Status packet (used to acknowledge

communication & provides a mean for error

correction)

USB cable connects peripheral device & master

device

USB std uses two types of connector for

connecting peripheral device & host device

- Type A

- Type B

Both these connectors have 4 pins for

communication

Each USB device has Product ID (PID) &

Vendor ID (VID)

PID & VID are essential for loading the

drivers corresponding to a USB device

• USB supports 4 types of data transfers

• 1. Control2. Isochronous3. Bulk4. Interrupt

• Control transfers exchange configuration, setup and command information between the device and the host. The host can also send commands or query parameters with control packets.

• Isochronous transfer is used by time critical, streaming device such as speakers and video cameras. It is time sensitive information so, within limitations, it has guaranteed access to the USB bus. Data streams between the device and the host in real-time, and so there will not be any error correction.

• Bulk transfer is used by device like printers & scanners, which receives data in one big packet. Here the timely delivery is not critical. Bulk transfers are fillers, claiming unused USB bandwidth when nothing more important is going on. The error correction protects these packets.

• Interrupt transfers is used by peripherals exchanging small amounts of data that need immediate attention. It is used by devices to request servicing from the PC/host. Devices like a mouse or a keyboard comes in this category. Error checking validates the data.

USB supports 4 different rates

- Low speed (1.5Mbps)

- Full speed (12Mbps)

- High speed (480Mbps)

- Super speed (4.8Gbps)

Low speed & Full speed are defined by USB1.0

High speed is defined by USB 2.0

Super speed is defined by USB 3.0

• USB Features

• The Universal Serial Bus has the following features:

• The computer acts as the host.

• Up to 127 devices can connect to the host, either directly or by way of USB hubs.

• Individual USB cables can run as long as 5 meters; with hubs, devices can be up to 30 meters

(six cables' worth) away from the host.

• With USB 2.0,the bus has a maximum data rate of 480 megabits per second (10 times the

speed of USB 1.0).

• A USB 2.0 cable has two wires for power (+5 volts and ground) and a twisted pair of wires to

carry the data. The USB 3.0 standard adds four more wires for data transmission. While USB

2.0 can only send data in one direction at a time (downstream or upstream), USB 3.0 can

transmit data in both directions simultaneously.

• On the power wires, the computer can supply up to 500 milliamps of power at 5 volts. A USB

3.0 cable can supply up to 900 milliamps of power.

• Low-power devices (such as mice) can draw their power directly from the bus. High-power

devices (such as printers) have their own power supplies and draw minimal power from the

bus. Hubs can have their own power supplies to provide power to devices connected to the

hub.

• USB devices are hot-swappable, meaning you can plug them into the bus and unplug them

any time. A USB 3.0 cable is compatible with USB 2.0 ports -- you won't get the same data

transfer speed as with a USB 3.0 port but data and power will still transfer through the cable.

• Many USB devices can be put to sleep by the host computer when the computer enters a

power-saving mode.

• The devices connected to a USB port rely on the cable to carry power and data.

THANK YOU…