22-01-2011, 06:14 PM
Inside USB:
The Basics
Appu Sajeev
2K7708
S7 CSE
The Basics
Appu Sajeev
2K7708
S7 CSE
Inside USB.pptx (Size: 350.18 KB / Downloads: 52)
Overview
Basic Concepts
Topology
Physical Specifications
Endpoints and Pipes
USB packet format
Transfer types
USB Enumeration
Building a USB Device
Universal Serial Bus
Fast, standard, serial interfacing protocol with handshaking
Auto detection and configuration
Upto 127 devices can be connected to one port, hubs can extend the number
Different versions:
USB 1.1 – form 1.5 Mbps(Low speed) up to 12Mbps (Full Speed)
USB 2.0 – up to 480 Mbps(Hi Speed)
USB 3.0 – up to 5 Gbps (Super Speed)
Topology
A hub is at the center of each star. Each wire segment is a point-to-point connection
Physical Specifications
Simple Interface, 2 wires for power (5V and GND) and 2 wires for serial data (D+ and D-). Can source a maximum of 500mA
D+ and D- form a differential pair, the voltage in on line is the is the inverse of other.
The data lines are NRZI (Non Return to Zero Inverted) encoded for synchronization. No explicit clock signal
USB packet format
Each USB transaction is divided into one or more transactions.
Each transaction involves 3 packets – Token packet, Data packet(optional) and handshake packet
Packets are grouped into frames that are released every 1 ms
Fields common to each packet
SYNC field – Used to synchronize the clocks of host and device. Denotes the start of a packet
8 bits for USB 1.1 devices and 32 bits for USB 2.0 devices