ITEC 352

Lecture 32USB

USB (1)

Review

• Exam• Intro/review of the bus system

USB (1)

Objectives

• Rationale• History of USB– Firewire

• Goal– Electricity to code

USB (1)

USB

• What do you know about it?• Why is it useful?• What alternatives can you think of?

USB (1)

History

• Started in 1994– Several companies participated

• High / low speed– 12 / 1.5 Mbits/s

• Development continues– USB 2.0 went up to 480 Mbits/s– USB 3.0 is up to 5 Gbit/s

USB (1)

Similar devices

• Firewire– Created by a different set of companies

• Designed for high-end audio/video transfer– Serial not parallel…Why?

• What differences do you think are made?– Keyboard versus camera

• Started at 400 Mbit/s (USB 1.0 = Molasses)–Went up to 800 Mbit/s

USB (1)

Serial versus parallel

• Getting data into a system• Modeling data sent over through– Serial– Parallel

• What are the advantages and disadvantages of each method

• Why do you think both types chose serial instead of parallel?

USB (1)

Topology

• One to one?• Many to one?• Many to many?• Anyone heard of hubs?• Is it synchronous or asynchronous?

USB (1)

Breakdown

• Allows sub-devices–Webcam = Video + Audio–Why is this important?

• 16 pipes– Two types: Stream and message–Why do think there is a need for two

types?

USB (1)

Transfer modes

• Isochronous transfers– Guaranteed rate but possible data loss

• Interrupt transfers– Quick response transfer

• Bulk transfers– Uses all available bandwidth– No guarantee on timing or latency

• Control transfers– Tell the device what to do

USB (1)

Connector

• Pin Layout (1-4)– Vcc +5V (Why is this important?)– Data-– Data+– Ground

USB (1)

Summary

• USB• Introduction / format• Next time– Physical mapping– Packets

• Friday– Code / libraries