USB Complete fourth- P3 ppsx

7UGUCPF.KOKVU USB is a likely solution any time you want to use a computer to communicate with an external device.. When a user connects a USB device to a PC, the operating system detect

At the start of each code example, a sidehead indicates the programming lan-guage:

The NET code is compatible with the NET Framework Version 2.0 and later

Example applications are available for free download from www.Lvr.com.

5KFGJGCF 2TQITCOOKPI.CPIWCIG 2TQXKFGT

VB Visual Basic NET Microsoft VC# Visual C# NET Microsoft PBP PICBASIC PRO microEngineering Labs, Inc.

C18 MPLAB C compiler for

PIC18 CPUs

Microchip Technology Inc.

xxi

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This book uses the abbreviations and symbols below to express quantities and units:

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p pico 10-12

n nano 10-9

µ micro 10-6

m milli 10-3

K kilo 210 (1024)

M mega 106 or 2 20 depending on context

G giga 109 or 2 30 depending on context

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A ampere

F farad

V volt

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s second

Hz Hertz (cycles per second)

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0WODGT5[UVGOU Binary values have a trailing subscript “b” Example: 10100011b An exception is when it’s clear from the context that the values are binary

Example: Set bits 6 5 to 01

Hexadecimal values have a trailing “h” Example: A3h.

All other values are decimal Example: 163.

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in inch

ft foot

m meter

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B byte bps bits per second

xxiii

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USB is much too big a topic to write about without help I have many people to thank

My technical reviewers provided feedback that helped make the book as com-plete and accurate as possible With that said, every error in this book is mine and mine alone A big thanks to Paul E Berg, Greg Burk, Robert Dunstan, John Garney, Bill Jacobus, Kosta Koeman, and Matt Leptich

Others I want to thank for their support are Phyllis Brown of J Gordon Elec-tronic Design, Michael DeVault of DeVaSys Embedded Systems, Traci Donnell

of the USB-IF, David Flowers of Microchip Technology, Inc., Laurent Guin-nard of Ellisys, Tim Harvey of CWAV, Inc., Blake Henry of Bitwise Systems,

John Hyde of usb-by-example.com, Rahman Ismail and Jeff Ravencraft of Intel

Corporation, Dr Bob Miller of Trace Systems, Inc., and Jeff Schmoyer of microEngineering Labs, Inc

For their help with the previous editions this edition builds on, thanks to Joshua Buergel, Gary Crowell, Fred Dart, Wendy Dee, Lucio DiJasio, Keith Dingwall, Dave Dowler, Mike Fahrion, David Goll, John M Goodman, Lane Hauck, David James, Christer Johansson, Geert Knapen, Alan Lowne, Jon Lueker, Brad Markisohn, Rich Moran, Bob Nathan, Walter Oney, Amar Rajan, Marc Reinig, Rawin Rojvanit, Glenn M Roberts, Robert Severson, Craig R Smith, and Dave Wright

I hope you find the book useful and welcome your comments at jan@Lvr.com.

1



75$$CUKEU

At over two billion new installed units per year, USB is the most successful per-sonal-computer interface ever Every recent PC has USB ports that can connect

to keyboards, mice, game controllers, scanners, cameras, printers, drives, and more USB is reliable, fast, versatile, power-conserving, inexpensive, and sup-ported by major operating systems USB 3.0’s new SuperSpeed bus means USB

is likely to continue to dominate as the interface of choice for an ever-expand-ing selection of peripherals

This chapter introduces USB, including its advantages and limits, some history about the interface and recent enhancements to it, and a look at what’s involved

in designing and programming a device with a USB interface

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USB is a likely solution any time you want to use a computer to communicate with an external device Internal devices, such as fingerprint readers, can use USB as well The interface is suitable for mass-produced, consumer devices as well as specialized, small-volume products and one-of-a-kind projects

Chapter 1

To be successful, an interface has to please two audiences: the users who want to use the devices and the developers who design the hardware and write the code that communicates with the devices USB has features to please both groups

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From the user’s perspective, the benefits of USB are ease of use, fast and reliable data transfers, low cost, and power conservation Table 1-1 compares USB with other interfaces

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Ease of use was a major design goal for USB, and the result is an interface that’s

a pleasure to use for many reasons:

One interface for many devices USB is versatile enough for just about any

standard PC peripheral function Instead of having a different connector and cable type for each peripheral function, one interface serves many

Automatic configuration When a user connects a USB device to a PC, the

operating system detects the device and loads the appropriate software driver The first time the device connects, the operating system may prompt the user to insert a disc with driver software, but other than that, installation is automatic Users don’t need to reboot before using the device

Easy to connect A typical PC has multiple USB ports, and hubs make it easy

to add ports without opening up the PC

Convenient cables USB connectors are small and compact compared to

con-nectors used by other interfaces such as RS-232 To ensure reliable operation, the USB specification defines electrical requirements for cables A cable seg-ment can be as long as 5 m depending on bus speed With hubs, again depend-ing on bus speed, a device can be as far as 30 m from its host PC

Wireless options USB originated as a wired interface, but technologies are

now available for wireless communications with USB devices

Hot pluggable Users can connect and disconnect a USB device whenever they

want, whether or not the system and device are powered, without damaging the

USB Basics

3

Table 1-1: USB is more flexible than other interfaces, which often target a

specific use.

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USB 3.0 dual simplex

serial

127 (per bus) 9 (typical)

(up to 49 with 5 hubs)

5 G Mass storage,

video

USB 2.0 half duplex

serial

127 (per bus) 16 (98 ft

with 5 hubs)

1.5M, 12M, 480M

Keyboard, mouse, drive, speakers, printer, camera

eSATA serial 2 (port

multiplier supports 16)

Ethernet serial 1024 1600 10G General network

communications IEEE-1394b

(FireWire 800)

serial 64 300 3.2G Video, mass

storage IEEE-488

(GPIB)

parallel 15 60 8M Instrumentation

I 2 C synchronous

serial

40 18 3.4M Microcontroller

communications Microwire synchronous

serial

8 10 2M Microcontroller

communications MIDI serial current

loop

2 (more with flow-through mode)

50 31.5k Music, show

control

Parallel Printer

Port

parallel 2 (8 with

daisy-chain support)

10–30 8M Printers,

scanners, disk drives

RS-232

(EIA/TIA-232)

asynchronous serial

2 50–100 20k (115k

with some hardware)

Modem, mouse, instrumentation

RS-485

(TIA/EIA-485)

asynchronous serial

32 unit loads (some chips allow up to

256 devices)

4000 10M Data acquisition

and control systems

SPI synchronous

serial

8 10 2.1M Microcontroller

communications

Chapter 1

No power supply required (sometimes) The USB interface includes

power-supply and ground lines that provide a nominal +5V from the PC or a hub A device that requires up to 500 mA (USB 2.0) or 900 mA (USB 3.0) can draw all of its power from the bus instead of using a dedicated power supply In contrast, devices that use other interfaces may have to provide a power supply inside the device or an external supply

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USB supports four bus speeds: SuperSpeed at 5 Gbps, high speed at 480 Mbps, full speed at 12 Mbps, and low speed at 1.5 Mbps SuperSpeed requires a USB 3.0 host controller in the host PC USB 2.0 host controllers support low, full, and high speeds

The bus speeds describe the rate that information travels on the bus In addi-tion to applicaaddi-tion data, the bus must carry status, control, and error-checking information Plus, multiple devices can share a bus Thus, the data throughput for an individual device’s data is less than the bus speed The USB protocols support data transfers at around 400 MB/s for SuperSpeed, 53 MB/s for high speed, 1.2 MB/s for full speed, and 800 B/s for low speed Hardware and soft-ware limitations can result in lower real-world rates, however

The USB 1.0 specification defined low and full speeds Full speed was intended for most peripherals that had been using RS-232 (serial) and parallel ports Full-speed data-transfer rates are comparable to the speeds of these earlier inter-faces Mice tend to use low speed because the less stringent cable requirements allow flexible cables Low-speed devices may have lower manufacturing cost due

in part to cheaper cables High speed became an option with the release of USB 2.0, and USB 3.0 defined SuperSpeed

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USB’s reliability is due to both the hardware and the protocols The hardware specifications for USB drivers, receivers, and cables ensure an electrically quiet interface that eliminates most noise that could cause data errors The USB pro-tocols enable detecting errors in received data and notifying the sender so it can

USB Basics

5

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Because the host computer provides most of the intelligence to control the interface, components for USB devices are inexpensive A device with a USB interface is likely to cost the same or less than an equivalent device with a differ-ent interface

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Power-saving circuits and protocols reduce a device’s power consumption while keeping the device ready to communicate when needed Reducing power con-sumption saves money, helps the environment, and for battery-powered devices, allows a longer time between recharges

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Many of the user advantages described above also make things easier for opers For example, USB’s cable standards and error checking mean that devel-opers don’t have to worry about specifying cable characteristics or providing error checking in software

Other advantages help the hardware designers who select components and design the circuits in devices and the programmers who write firmware embed-ded in the devices and software to communicate with devices

The benefits result from the flexibility built into the USB protocol, the support

in the controller chips and operating system, and the support available from the USB Implementers Forum

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USB’s four transfer types and four speeds make the interface feasible for many types of peripherals USB has transfer types suited for exchanging large and small blocks of data, with and without time constraints For data that can’t tol-erate delays, USB can guarantee bandwidth These abilities are especially wel-come under Windows where accessing peripherals in real time is often a challenge Although the operating system, device drivers, and application soft-ware can introduce unavoidable delays, USB makes it as easy as possible to achieve transfers that are close to real time even on desktop systems

Unlike other interfaces, USB doesn’t assign specific functions to signal lines or make other assumptions about how the system will use the interface For exam-ple, the status and control lines on the PC’s parallel port were defined with the