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PC PeripheralsPC Peripherals for for TechniciansTechnicians Chapter 1.3 - Chapter 1.3 -

Interfaces: USBInterfaces: USB(Universal Serial Bus)(Universal Serial Bus)

Systems Manufacturing Training Systems Manufacturing Training and Employee Developmentand Employee Development

Copyright © 1998 Intel Corp.Copyright © 1998 Intel Corp.

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USB OverviewUSB OverviewOBJECTIVES: At the end of this section, the

student will be able to do the following: List features & applications of the Universal Serial Bus Explain the Topology of the USB Describe USB Cables and Connections Discuss USB Bus transactions

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Why Universal Serial Bus? Historically adding functionality to the PC has been

problematic for the user:Limited external standard ports:

» Serial; Parallel

Add-in card configuration:» Dip switches; jumper cables; IRQ settings; DMA channels;

I/O addresses; software drivers.

PC User Experience:» Time consuming; high-risk; fear of system crashing

USB allows simpler addition of peripherals to PC's.Projected to replace many existing peripheral-to-host

protocols (e.g. RS-232), allowing many peripherals to connect to PC through the same type of port.

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Why Universal Serial Bus?

USB ConnectorsGraphics

PortLAN

USB USB USB

Keyboard

Mouse

SerialPort

ParallelPort

SCSIPort

Sound/Game

GraphicsPort

LANLAN Modem

USB

Initially, USB is an addition to existing interfaces.

BEFORE .... AFTER ...Gradual Transition

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Universal Serial Bus - Overview USB is a bi-directional, dynamically attachable, host-

driven serial interface for adding peripheral devices on a single bus. USB uses a single connector for keyboards, mice, serial

devices, digital audio, printers, etc.The USB provides a new serial protocol for sending data

between a PC and peripherals.USB enables low & medium speed I/O devices to be

connected without card insertions or reconfiguration.

USB was jointly developed by Compaq, Digital Equipment, IBM, Intel, Microsoft, NEC, and Nortel.The USB specification is royalty-free and openly

available.

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Universal Serial Bus - Features USB Features Summary:

Plug & play “outside the box”» Supports hot-plugging

» Supports up to 127 devices

Single connector across all devices» Up to 5 meters per cable segment

» Built-in power distribution

12 Mb/s throughput--for highest performance» Low-speed option (1.5 Mb/s)--for lowest cost

2-wire differential signalingAsynchronous and isochronous support

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Universal Serial Bus - Features Allows virtually unlimited expansion “outside the box.”

Can connect up to 127 daisy-chained devices.» Breaks the traditional log jam associated with the limited

number of serial and parallel expansion connectors or PC card slots available for port expansion.

Supports hot-plugging: » Enables devices to be connected to the PC without card

insertions, reconfiguration or powering down the computer.

Dynamic insertion-removal and autoconfiguration on change.

» If the devices and the OS support Plug and Play, the appropriate device drivers can automatically load and unload without user intervention.

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Universal Serial Bus - Features USB employs a “one-size-fits-all” industry-standard

connector and socket interfaceCables have only 4 wires, allowing compact connectors.USB cable +5-volt power distribution eliminates the need

for AC power supply boxes for low/bus-powered devices.

Data transfer rate of 12Mbits/second supports a wide variety of desktop peripherals:Low-speed 1.5 Mbit/second option supports low-end,

low-speed devices such as key-boards and mice for further cost reduction.

Isochronous transfers (such as audio), get top priority, assuring that time-sensitive data streams are not interrupted.

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Universal Serial Bus - Applications USB eliminates need for mouse port, keyboard port,

and eventually for serial and parallel portsKeyboard, mouse, trackballPrinters and scannersGame peripherals (Joystick)Modem or ISDN/PBX interface4x & 6x CD ROM drives and floppy drivesDigital audio interface - Eliminates need for an analog

audio connection for speakers and microphones.» Speakers and microphones could be built into monitor.

Monitor - Control Only (Contrast, Brightness, Colors, etc.)

» Video Signals are not managed (uses separate connection)

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Universal Serial Bus - Applications

USB in 1997:An incremental Connector for new applications

1394.x Optional Add-in Card

USB Future:The PC evolves into a simpler, easier to use appliance.

Keyboard

Mouse

SerialPort

ParallelPort 1394.x

Sound/GamePorts

GraphicsPort

LAN Modem

USB

1394

.x C

ard

Graphics LAN

1394.xUSB

Telephony, Modem,Kyb, Mouse, Joystick,Still/ Motion Camera,Digital Audio, Backup Store,Printer, Scanner,Wireless Adapters

DigitalVideo, ConsumerElectronics,Storage

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Universal Serial Bus - Applications

USB and IEEE1394 Are Complementary Technologies

Digital VCRDVD-RAM

DV Camcorder

“NIC”DSS

Keyboard Mouse

Joystick

Phone

1394 Domain 1394 Domain

Video ConfCamera

AudioPersonal PrintersTape BackupFloppy

USB Domain USB Domain

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Universal Serial Bus - Applications USB Focus on Low Cost, High Volume Applications

USB is targeted at devices requiring relatively low bandwidth (10Mb/s or less).

The USB, tiered star approach is cheap for downstream nodes, but requires a central host.

IEEE 1394 is more expensive and has a different design focus.IEEE 1394 (FireWire) has no central host, and therefore

requires a complete controller at each node.IEEE 1394 is targeted at applications requiring 100Mb/s+

bandwidth which is not needed for most PC peripherals.» Digital VCRs and other consumer electronics require the

bandwidth provided by IEEE 1394.

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Universal Serial Bus - Topology

SCSI

BUS

LAN

LANAdapter

SCSIHost BusAdapter

PCI Bus

GraphicAdapterCPU CPU Local Bus

Host/PCI

BridgeMemory Bus

Keyboard(Hub)

Monitor(Hub)

USB Host Ctlr (e.g PIIX3)

(Root Hub)

Tape

Disk

CDROM

Mouse Speakers

USBPort

MainMemory

The Universal Host Controller is integrated into the PIIX3 (and later) PCI-ISA Expansion Bridge chips.

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Universal Serial Bus - TopologyHost: Initiates all transactions under software control.

Hub: Provides connecting ports and power.

Device: A Peripheral that attaches to the USB.

5m

5m

5m

5m

5m

Host Hub

Device

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Universal Serial Bus - TopologyThe USB physical interconnect is a tiered star topology.

Each segment is a point-to-point connection between the host and a hub/device, or a hub connected to another hub or device.

A hub is at the center of each star. Up to 5 meters per segment Up to 127 devicesUp to 6 tiers

USB has the concept of a HUB: A device whose purpose is to allow the connection of additional devices.

Host (Root Tier)

Tier 1

Tier 2

Tier 3

Tier 4

Hub 1

Hub 2 Port

Host

Port

Hub 3 Hub 4 Port Port

PortPortPort

RootHub

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Universal Serial Bus - Topology Each USB Hub converts a single attachment point into

multiple attachment points (ports).A USB Hub expands a single connection, or port (termed

the upstream port), to two or more downstream ports.Peripherals can act as Hub devices so only 1 peripheral

device must be plugged directly into the host PC.» A Hub may have integrated device(s)--the combination is

known as a compound device.

A Hub provides attach/detach detection.A Hub also provides electrical safety services.

» Automatically reports to the host every over-current event.

» Shuts down the downstream power to all four ports when total load exceeds 400mA.

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Universal Serial Bus - Topology USB supports 100mA and 500 mA current levels.

Max current available is 500mA for bus powered devices.Minimum current available at a port is 100mA (1 load).

Hubs may be self-powered or bus-poweredUnpowered devices (e.g. mice) can be attached to

powered hubs--power distributed over the USB cabling.» A bus-powered hub draws electrical current (500ma)

directly from its upstream connection to the USB.> It delivers 100ma to each of its 4 downstream connections,

using the remaining power for its own operation.

» Note: The USB spec. does not permit the connection of an additional bus-powered hub to one of the downstream ports of a bus-powered hub; the downstream hub must be self-powered (i.e., have its own power supply).

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USB Cables and Connections Physical Layer

4 pin connector, 4 wire cableSupply Sourcing +5V2-wire differential signalingCMOS signal levels @ 3.3V

In most cases a USB cable should be captive (molded in) to it's peripheral.The series "A" connector is a plug for a

peripheral and a socket for a PC platform.The series "B" connector (detachable)

was created for applications where a captive cable is prohibitive.

Power pair

Differential Signal pair

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USB Cables and Connections Connectors

4-Position with shielded housingPositive RetentionBlind Mating CapabilitiesStaggered power/data pins in plug

» Insures power will not flow through data lines

Cables have only four wires, allowing compact connectors roughly as wide as a staple.Small size is important for notebooks &

downsized desktop PCs.

Plug

Plug

~9.7 mm

~ 8.65 mm

+5 D- D+ Gnd

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USB Cables and Connections

-

+

D+

D-

Rcv Data

DifferentialReceiver

Xmt Data

DifferentialDriver

-

+

D+

D-

Rcv Data

DifferentialReceiver

Xmt Data

DifferentialDriver

D+

D-

USB Cable

Upstream Port (HUB)e.g. PC

Downstream Porte.g. Digital Video Camera

Bi-directional, half-duplex linkThe Differential Receiver amplifies the difference between

the incoming data lines.» Communication toward the host PC is called upstream

» Communication toward the devices is called downstream.

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USB Cables and Connections

Cables: 20-28 AWG for power; 28 AWG for signaling Full-Speed--Twisted & Shielded cable

USB runs at 12 Mbit / sec Full Speed (F.S.) bit rate

Low-Speed Mode--Unshielded & Untwisted cable1.5 Mbit / sec Low Speed (L.S.) bit rate (1.5Mbps sub-channel)Saves EMI suppression costs and allows very-low-cost devices to

be built without compromising data rate for faster devices. Mice, keyboards, and most other user interface peripherals don’t

need fast data rate.

5 meters max

...

...

+5V

GND

D+D-

+5V

GND

D+D-

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USB Cables and Connections

D-

D+

R1

R1 = 15K±5%R2 = 1.5K±5%

Twisted Pair, Shielded

Untwisted, Unshielded

F.S./L.S. USBTransceiver

(45Outputs)

Host or Hub Port

ZO = 90 5 Meters Max.

F.S. USBTransceiver

(45Outputs)

Hub Port 0or

Full Speed Function

R1

R2

D-

D+

R1

R1 = 15K±5%R2 = 1.5K±5%

F.S./L.S. USBTransceiver

(45Outputs)

Host or Hub Port

3 Meters Max.

F.S. USBTransceiver

(45Outputs)

Low Speed FunctionR1

R2

D+

D-

D+

D-

Differential signal pair

Device Connect Detection

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USB Cables and Connections Pull-down resistors on the D+ and D- lines ensure that both

data lines are near ground when no device is attached. USB devices have a pull-up resistor on either D+ or D-

When D+ (Full Speed) or D- (Low Speed) rise above 2VDC for longer than 2.5 us, the HUB recognizes device attachment.

Host software periodically polls each HUB to check for device attachment and detachment

Full Speed Device Connect Detection

DeviceConnected

D-

D+

ConnectDetected

VOH (min)

VIH (max)

VIL (min)VOL (max)VSS

2.5 s

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USB Bus TransactionsUSB uses 7 bits to address each device on the bus.

The USB Host Controller broadcasts tokens on the bus and a device that detects a match on the address in the token responds by either accepting data or sending data to the host.

HUBHUB HOST/HUB

Monitor

SpeakerPen Mouse

Kbd

Mic Phone

PC

USB has automatic address selection, no terminators, and locations on the bus are arbitrary.

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USB Bus Transactions USB transfers data at regular intervals called frames.

All bus activity is controlled and directed by the host.

Four transfer types (Control, Interrupt, Bulk, Isochronous) enable a variety of peripherals:Control (e.g.: Configuration, Messages)

» Bi-directional; Used for bus management, configuration, device control, & status information.

Interrupt (e.g.: Keyboard, Mouse, Joystick) » Designed to support Human Input Devices (HID) such as

joysticks, mice, & keyboards.

» Used to poll devices to see if they have data to transfer.

» Asynchronous, non periodic, low bandwidth, response time sensitive.

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USB Bus TransactionsBulk (e.g.: Printer, Scanner, Still camera)

» Enables devices like printers to communicate large amounts of data as bus bandwidth becomes available.

» Stream, NO guaranteed bandwidth.

» Asynchronous, non periodic, high bandwidth utilization.

» Used for data that may be bursty, less time-sensitive.

Isochronous (e.g.: Audio, Telephony)» Isochronous transfers get top priority, assuring that time-

sensitive data streams are not interrupted.

» Unidirectional, no handshake, no guaranteed delivery.> Based on time slices rather than handshaking. > No retry in the event of delivery failure or error.

» Media access controlled by host.

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REVIEW & SUMMARY USB Features

Plug & play “outside the box”» Up to127 devices; Hot-plugging; Autoconfig. on change

Single connector across all devices» Built-in power distribution; 2-wire differential signaling

12 Mb/s throughput--for highest performance» Low-speed option (1.5 Mb/s)--for lowest cost

Asynchronous and isochronous support USB Applications

Telephony, Modem, Kyb, Mouse, Joystick, Still/ Motion Camera, Digital Audio, Printer, Scanner, 4x/6x CD ROM, Floppy drives, & Monitor (control only).

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REVIEW & SUMMARY USB Topology

Tiered Star (Distributes Connectivity Points) 127 devices + hostUp to 6 tiers (up to 5 meters per segment)

USB Cables and Connections2-wire differential signalingSupply Sourcing +5V4 pin connector, 4 wire cable

Power pairPower pair

Differential Signal pairDifferential Signal pair

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REVIEW & SUMMARY USB Bus transactions

Media access controlled by hostSpeed: 12Mbps full speed; 1.5Mbps sub-channelFour transfer types enable a variety of peripherals:

» Control (e.g.: Configuration, Messages)

» Interrupt (e.g.: Keyboard, Mouse, Joystick)

» Bulk (e.g.: Printer, Scanner, Still camera)

» Isochronous (e.g.: Audio, Telephony)

BEFORE .... AFTER ...

End of Chapter 1-3