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3. Buses. Introduction Electrical Considerations Data Transfer Synchronization Bus Arbitration VME Bus Local Buses PCI Bus PCI Bus Variants Serial Buses. Serial Buses. Serial Buses I 2 C Bus USB. Serial Buses. Viable alternatives to parallel buses Advantages :

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3 buses

3. Buses

  • Introduction

  • Electrical Considerations

  • Data Transfer Synchronization

  • Bus Arbitration

  • VME Bus

  • Local Buses

  • PCI Bus

  • PCI Bus Variants

  • Serial Buses

Input/Output Systems and Peripheral Devices (03-4)


Serial buses

Serial Buses

  • Serial Buses

    • I2C Bus

    • USB

Input/Output Systems and Peripheral Devices (03-4)


Serial buses1

Serial Buses

  • Viable alternatives to parallel buses

  • Advantages:

    • Smaller connectors

    • Reduced susceptibility to electrical interferences

    • Longer interconnection distance

    • Higher reliability

    • Lower cost of the interface

Input/Output Systems and Peripheral Devices (03-4)


Serial buses2

Serial Buses

  • Serial Buses

    • I2C Bus

    • USB

Input/Output Systems and Peripheral Devices (03-4)


I 2 c bus

I2C Bus

  • I2C Bus

    • Overview

    • Start and Stop Conditions

    • Data Transfers

    • Bus Variants

Input/Output Systems and Peripheral Devices (03-4)


Overview 1

Overview (1)

  • I2C (Inter-Integrated Circuits) – Philips

  • Bidirectional bus with two wires:

    • SDA (Serial Data)

    • SCL (Serial Clock)

Input/Output Systems and Peripheral Devices (03-4)


Overview 2

Overview (2)

  • A device connected to the I2C bus can operate as:

    • Receiver

    • Transmitter and receiver

  • Each device has a unique address

  • Transmitters and receivers can operate either in master or slave mode

  • Multiple master devices can be connected to the bus

    • Arbitration procedure

Input/Output Systems and Peripheral Devices (03-4)


I 2 c bus1

I2C Bus

  • I2C Bus

    • Overview

    • Start and Stop Conditions

    • Data Transfers

    • Bus Variants

Input/Output Systems and Peripheral Devices (03-4)


Start and stop conditions 1

Start and Stop Conditions (1)

  • Generated by the master device

  • Start condition:

    • 1  0 transition on the SDA line, SCL = logical 1

  • Stop condition:

    • 0  1 transition on the SDA line, SCL = logical 1

Input/Output Systems and Peripheral Devices (03-4)


Start and stop conditions 2

Start and Stop Conditions (2)

  • Data on the SDA line must be stable while SCLis logical 1

  • Data can be changed only when SCL is logical 0

Input/Output Systems and Peripheral Devices (03-4)


I 2 c bus2

I2C Bus

  • I2C Bus

    • Overview

    • Start and Stop Conditions

    • Data Transfers

    • Bus Variants

Input/Output Systems and Peripheral Devices (03-4)


Data transfers 1

Data Transfers (1)

  • Categories of information sent on the I2C bus:

    • Startbit

    • Slave device address (7 or 10 bits)

    • Read/write bit

    • Data bits (segments of 8 bits each)

    • Acknowledge bit (after each data segment)

    • Stopbit

Input/Output Systems and Peripheral Devices (03-4)


Data transfers 2

Data Transfers (2)

  • Example transfer

    • The number of bytes in a transfer is not restricted

    • The receiver can force the transmitter into a wait state

Input/Output Systems and Peripheral Devices (03-4)


Data transfers 3

Data Transfers (3)

  • Three formats for data transfers:

    • Write data from a master transmitter to a slave receiver

    • Read data by a master device

    • Multiple read and write transfers

  • The address and direction of data are encoded in the first byte after the start bit

    • LSB = 0: write data from master

    • LSB = 1: read data from slave

Input/Output Systems and Peripheral Devices (03-4)


I 2 c bus3

I2C Bus

  • I2C Bus

    • Overview

    • Start and Stop Conditions

    • Data Transfers

    • Bus Variants

Input/Output Systems and Peripheral Devices (03-4)


Bus variants 1

Bus Variants (1)

  • Original I2C bus

    • Maximum transfer rate of 100 Kbits/s

    • 7-bit addresses

  • Version 2.0

    • Fast transfer mode, max. 400 Kbits/s

    • 10-bit addresses

    • Possibility to connect devices with 7-bit or 10-bit addresses

Input/Output Systems and Peripheral Devices (03-4)


Bus variants 2

Bus Variants (2)

  • Version 2.1

    • Shifting of voltage levels (Level-shifting) in order to connect devices with different supply voltages

    • Extended specifications for devices with voltages below 2.7 V

    • High-speed transfer mode →maximum 3.4 Mbits/s

Input/Output Systems and Peripheral Devices (03-4)


Serial buses3

Serial Buses

  • Serial Buses

    • I2C

    • USB

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Introduction

Introduction

  • USB – Universal Serial Bus

  • Developed in 1995 by a group of companies: HP, Compaq, Intel, Lucent, Microsoft, NEC

  • USB Implementers Forum (www.usb.org)

  • Motivation:

    • Simplify the connections with peripherals

    • Provide high data transfer rates

    • Ease of use (“Plug and Play”)

    • Eliminate the restrictions due to insufficient hardware resources

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Features

Features

  • Detects when a new peripheral is added

  • Determines the resources it needs

  • Adding and removing a peripheral can be done without shutting down the computer

  • A tree-like interconnection is possible, with up to 127 peripherals

  • The peripherals are powered with +5 V through the cable

  • Master/slave (host/device) architecture: data transfers initiated by the master

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Bus topology 1

Bus Topology (1)

  • Hubs

  • Functions (devices)

Input/Output Systems and Peripheral Devices (03-4)


Bus topology 2

Bus Topology (2)

  • USB Hubs

    • Recognize dynamic attachment of a peripheral

    • Provide a power of at least 0.5 W for each peripheral during initialization

    • Can provide a power of up to 2.5 W for peripheral operation

    • Each hub consists of:

      • Repeater: switch

      • Controller: interface registers for communication with the host

Input/Output Systems and Peripheral Devices (03-4)


Bus topology 3

Bus Topology (3)

  • Upstream port (for host)

  • Downstream ports (for functions)

  • Cascaded connection up to 5 levels

Input/Output Systems and Peripheral Devices (03-4)


Bus topology 4

Bus Topology (4)

Input/Output Systems and Peripheral Devices (03-4)


Bus topology 5

Bus Topology (5)

  • USB Functions

    • USB peripherals that are able to transmit or receive data or control information

    • A peripheral may contain multiple functions

    • Must respond to transaction requests sent by the host

    • Contain configuration information that describe their capabilities and resources needed

    • Configuringa function: allocating bandwidth and selecting configuration options

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Usb versions 1

USB Versions (1)

  • Version 1.0 (1995): max. 12 Mbits/s

  • Version 1.1 (1998): max. 12 Mbits/s

    • Low-speed channel (1.5 Mbits/s)

  • Version 2.0 (2000)

    • The maximum transfer rate increased 40 times, to 480 Mbits/s (High-Speed)

    • Uses the same cables, connectors, and software interfaces

    • Allows to use new types of peripherals: video cameras, scanners, printers

Input/Output Systems and Peripheral Devices (03-4)


Usb versions 2

USB Versions (2)

  • USB On-The-Go (USB OTG)

    • Supplement to USB 2.0 specification (2006)

    • A device may have either the master or slave role (host, peripheral)

      • Protocol to exchange the host/peripheral role

    • Two devices can communicate with each other without a computer

      • Tablet  printer

      • Printer  camera

Input/Output Systems and Peripheral Devices (03-4)


Usb versions 3

USB Versions (3)

  • Version 3.0

    • Specifications completed in 2008 by the USB 3.0 Promoter Group

    • SuperSpeed mode: 5 Gbits/s

    • Two simplex differential channels in addition to the existing differential channel  a total of 8 wires

    • Technology is similar to PCI Express 2.0 8b/10b encoding (500 MB/s)

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Cables and connectors 1

Cables and Connectors (1)

  • Differential signals on the D+ and D- wires

  • Supply voltage for peripherals on the VBUS wire

  • Terminations at each end of the cable

    • Provide correct voltage levels for peripherals

    • Allow detection of attach and detach of devices

    • Differentiate between full- and low-speed devices

Input/Output Systems and Peripheral Devices (03-4)


Cables and connectors 2

Cables and Connectors (2)

  • The original USB specification defines Type-A and Type-B plugs and sockets

  • Hosts and hubs: Type-A socket (rectangle)

  • Peripherals: Type-B socket (square)

  • In general, cables have only plugs

Input/Output Systems and Peripheral Devices (03-4)


Cables and connectors 3

Cables and Connectors (3)

  • The data connectors in the Type-A plug are recessed compared to the power connectors

  • Some devices operate in a different mode when the connector is only partially inserted

Input/Output Systems and Peripheral Devices (03-4)


Cables and connectors 4

Cables and Connectors (4)

  • Mini-USB and micro-USB connectors for tablets, mobile phones, cameras

  • Mini-USB: 7 x 3 mm; not used in new devices

  • Micro-USB: 7 x 1.5 mm

Input/Output Systems and Peripheral Devices (03-4)


Cables and connectors 5

Cables and Connectors (5)

  • USB OTG

    • Micro-AB sockets

    • Allow to connect either a micro-A or a micro-B plug

    • An ID pin: used to detect the type of the plug inserted

      • Grounded in micro-A, floating in micro-B

      • If an A plug is connected: host role  power supplier

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Electrical interface

Electrical Interface

  • Data are encoded  generation of a receive clock signal is simplified

  • The encoding used is NRZI(Non Return to Zero Inverted)

    • Bits of 1 and 0 are represented by opposite and alternating voltages, without return to zero voltage between encoded bits

  • Bit stuffing to ensure enough transitions of the transmitted signals

Input/Output Systems and Peripheral Devices (03-4)


3 buses

USB

  • USB

    • Introduction

    • Features

    • Bus Topology

    • USB Versions

    • Cables and Connectors

    • Electrical Interface

    • Transfer Types

Input/Output Systems and Peripheral Devices (03-4)


Transfer types 1

Transfer Types (1)

  • Control Transfers

    • Used by the host drivers to configure the peripherals

  • Bulk Transfers

    • Consist of large amounts of data

    • Used for printers, scanners etc.

    • Reliability ensured by: error detection code; retries of erroneous transfers

    • Transfer rate can vary

Input/Output Systems and Peripheral Devices (03-4)


Transfer types 2

Transfer Types (2)

  • Interrupt Transfers

    • Used for small amounts of data

    • A data transfer may be requested by a peripheral at any time

    • The transfer rate cannot be lower than that specified by the peripheral

    • Data consist of event notification, characters, or coordinates

Input/Output Systems and Peripheral Devices (03-4)


Transfer types 3

Transfer Types (3)

  • Isochronous Transfers

    • Isos – equal, uniform; chronos – time

    • Isochronous – with equal duration; that occurs at equal intervals

    • Used for data generated in real time, that must be delivered at the rate at which data are received

    • The maximum delivery delay must also be ensured

Input/Output Systems and Peripheral Devices (03-4)


Transfer types 4

Transfer Types (4)

  • The timely delivery of data is ensured at the expense of potential losses in the data stream

  • Dedicated portion of bandwidth

  • Isochronous transfers:

    • Timely data delivery

    • Lack of retries for erroneous data

  • Asynchronous transfers:

    • Correct data delivery

    • Retries for erroneous data

Input/Output Systems and Peripheral Devices (03-4)


Summary 1

Summary (1)

  • Serial buses have several advantages compared to parallel buses

  • The I2C bus has been developed for the communication between microcontrollers and various peripherals

    • To achieve bus control, a start condition has to be generated

    • To release the bus, a stop condition has to be generated

    • Each byte sent is followed by an acknowledge bit Ack

Input/Output Systems and Peripheral Devices (03-4)


Summary 2

Summary (2)

  • Motivations for developing the USB: simplifying the connections with peripherals; higher data transfer rates; ease of use

    • When a peripheral is attached, its required resources are determined

    • Star topology, with hubs and functions

  • The USB OTG version enables a USB device to initiate transfers with another device

  • The USB 3.0 version uses a technology similar to that of the PCI Express 2.0 bus

Input/Output Systems and Peripheral Devices (03-4)


Summary 3

Summary (3)

  • The electrical interface uses the NRZI encoding

  • The USB allows several types of data transfers:

    • Control transfers

    • Bulk transfers

    • Interrupt transfers

    • Isochronous transfers

  • Isochronous transfers enable to allocate a dedicated portion of bandwidth for data generated in real time

Input/Output Systems and Peripheral Devices (03-4)


Concepts knowledge 1

Concepts, Knowledge (1)

  • Advantages of serial buses

  • Overview of I2C bus

  • Start and stop conditions

  • Data transfers on the I2C bus

  • I2C bus variants

  • Features of USB

  • USB hubs

  • USB functions

Input/Output Systems and Peripheral Devices (03-4)


Concepts knowledge 2

Concepts, Knowledge (2)

  • USB OTG version

  • USB 3.0 version

  • The role of USB terminators

  • The electrical interface of USB

  • Transfer types on the USB

  • Bulk transfers

  • Interrupt transfers

  • Isochronous transfers

Input/Output Systems and Peripheral Devices (03-4)


Questions

Questions

  • What are the advantages of serial buses?

  • What are the main features of the USB bus?

  • How can a USB host determine the capabilities and resources needed by a USB function?

  • What is the difference between isochronous and asynchronous transfers?

Input/Output Systems and Peripheral Devices (03-4)


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