Understanding USB ConceptsUniversal Serial Bus

Step by Step Tutorial

IMBUENT TECHNOLOGIES PVT. LTD.

Ludhiana, Punjab,India

Universal Serial Bus : Introduction

� The Universal Serial Bus (USB) is one of the most common

interfaces used in electronic consumer products today, including

PCs, cameras, GPS devices, MP3 players, modems, printers,

and scanners, to name a few.

� The USB was originally developed by

• Compaq,

• Microsoft, • Microsoft,

• Intel,

• and NEC,

• and later by Hewlett-Packard, Lucent, and Philips as well.

These companies eventually formed the nonprofit corporation USB

Implementers Forum Inc. to organize the development and publication

of USB specifications.

2

Cont’d:

The USB is four-wire serial cable of up to three or even five meters in length.

The USB is a high-speed serial interface that can also provide power to devices connected to it. A USB bus supports up to 127 devices.

A device can be plugged into a hub which is plugged into another hub, and so on. The maximum number of tiers permitted is six.

3

so on. The maximum number of tiers permitted is six.

For longer-distance bus communications, other methods such as use ofEthernet are recommended.

Who Developed USB?

Universal Serial Bus (USB) is a specification[1] to establish communication between

devices and a host controller (usually a personal computer), developed and invented

by Ajay Bhatt while working for Intel.

4

USB Device

1) USB as Host Like .. USB based Audio, Video Player

1) USB as DeviceLike.. USB Based Pen Drive, Mouse

1) USB as OTG (On- to – Go)Latest One. Same device will acts Host and Device using Same

5

Latest One. Same device will acts Host and Device using SameBus(Signals) Like.. Nokia N8 Mobile.

USB On-The-Go, often abbreviated USB OTG, is part of a supplement[1] to the USB 2.0 specification originally agreed upon

in late 2001 and later revised.[2] The specification allows for devices that generally fulfill the role of being a slave USB device

(which might be, e. g. digital audio player or mobile phone) to a USB host (usually a desktop or notebook computer) to

become the host themselves when paired with another USB device. The latest version of the supplement also defines

behavior for an Embedded Host which has targeted capabilities and the same USB Standard-A port used by PCs.

Source:http://en.wikipedia.org/wiki/USB_On-The-Go

1.USB Fundamentals:

Bus Specifications:

Low speed —1.5Mb/secFull speed —12Mb/secHigh speed — 480Mb/sec (Version USB 2.0)Super Speed — 5.0 Gbit/sec (Latest Version USB 3.0)

Wireless USB - 53 - 480 Mbit/s (in 3-10 meter)

6

Wireless USB - 53 - 480 Mbit/s (in 3-10 meter)

The maximum power available to an external device is limited to about 100mA at 5.0V

Advertisement:

EMBEDDED TRAINING IN LUDHIANA

PUNJAB, INDIA

8051/ PIC / ARM / EMBEDDED LINUX

7

www.imbuent.com

2. USB Connector (s):

� USB device comes with their own USB cable, which may have

two type of connectors

• A Type Connector

• B Type Connector

� A Type Connector

• This connector goes to computer A type Connector• This connector goes to computer

• This is upstream connector

� B Type Connector

• This connector goes to device side

• This is downstream connector

8

A type Connector

B type Connector

2. Mini USB Connector (s): Cont’d

9

Source: http://en.wikipedia.org/wiki/Universal_Serial_Bus#Physical_appearance

3. USB Pin Assignment:

USB is a four-wire interface implemented using a four-core shielded cable. Two

types of connectors are specified and used.

10

4. USB Signals

� USB signals are bi-phase, and signals are sent from the host

computer using the NRZI (non-return to zero inverted) data

encoding technique

11

5. USB Speed Specifications

USB has four Signals i.e. Vbus, D+ , D- ,GND

For Full Speed Bus:

If D- must be having pulled up resistance with +5V.

For Low Speed Bus:

12

For Low Speed Bus:

If D+ must be having pulled up resistance with +5V.

When no device is plugged in, the host will see both data lines as low. Connecting a device to the

bus will pull either the D+ or the D- line to logic high, and the host will know that a device is

plugged into the bus

6. USB Transaction:

Data is transmitted on a USB bus in packets. A packet starts with a sync pattern to allow

the receiver clock to synchronize with the data. The data bytes of the packet follow,

ending with an end of packet signal.

There are four packet formats, based on which PID is at the start of the packet:

1. Token packets,

2. Data packets,

3. Handshake packets

4. Special packets

13

7. USB Transfer:

•Bulk transfer:

•Interrupt transfers:

•Isochronous transfers:

•Control transfer:

14

•Control transfer:

8.Enumeration:

When a device is plugged into a USB bus, it becomes known to the host through a process called enumeration (Means Part of Host i.e. Host)

15

9. Descriptor:

All USB devices have a hierarchy of descriptors that describe various features of

the device: the manufacturer ID, the version of the device, the version of USB it

supports, what the device is, its power requirements, the number and type of

endpoints, and so forth.

16

The most common USB descriptors are:

• Device descriptors

• Configuration descriptors

• Interface descriptors

• HID descriptors

• Endpoint descriptors

Some common USB terms are:

HID : Human Interface Device

PID : Product ID

VID : Vendor ID

Endpoint: An endpoint is either a source or a sink of data. A single

USB device can have a number of endpoints, the limit being

sixteen IN and sixteen OUT endpoints.

Transaction: A transaction is a transfer of data on the bus.Transaction: A transaction is a transfer of data on the bus.

Pipe: A pipe is a logical data connection between the host and an

endpoint.

Note: Vendor IDs are unique throughout the world and are issued by the USB implementers

. Please Log on to www.usb.org

Where to Get VID?? : http://www.usb.org/developers/vendor/

17

Examples: USB Device Class (HID)

18

Advertisement:

EMBEDDED TRAINING IN LUDHIANA

PUNJAB, INDIA

8051/ PIC / ARM / EMBEDDED LINUX

19

www.imbuent.com

Embedded USB: USB in MCUs

Microchip PIC18F4550 Host/Device

PIC24FJ256GB110 Host/Device

NxP LPC2148 Host/Device

TI LM3S9B90 Host/Device/USB On-to-Go

NxP LPC1768 Host/Device/USB On-to-Go

Microchip PIC32MX440F512H Host/Device/USB On-to-Go

20

Why USB??

1) USB Devices are plug and play.

2) Speed:USB is much faster than Traditional Communication Techniques like Serial,

Parallel

3) Implementation: Only Four Wires needs for USB.

4) Self Power and Low Cost

5) Size: Varity of Connectors available for USB interface.

21

6) Adaptation: USB interface is adapted by No. of Devices for different manufactures in All

Most all domain like Consumer, Industrial,Domestic applications for facilitate the user in

terms Of accessibility of use as well as upgradation of system.

How to Check USB Detail ?

22

USB Viewer:

23

http://www.ftdichip.com/Support/Utilities.htm

Example : Kingston USB Pen Drive

24

Thanks

http:// www.embeddedcraft.orghttp:// www.embeddedcraft.org

embeddedcraft@googlegroup.com

query@embeddedcraft.com