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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)

slide19
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)

slide21
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)

slide23
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)

slide29
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)

slide33
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)

slide39
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)

slide41
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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