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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. Serial Buses. Serial Buses I 2 C Bus USB. Serial Buses. Viable alternatives to parallel buses Advantages :

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3. Buses

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  1. 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)

  2. Serial Buses • Serial Buses • I2C Bus • USB Input/Output Systems and Peripheral Devices (03-4)

  3. 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)

  4. Serial Buses • Serial Buses • I2C Bus • USB Input/Output Systems and Peripheral Devices (03-4)

  5. I2C Bus • I2C Bus • Overview • Start and Stop Conditions • Data Transfers • Bus Variants Input/Output Systems and Peripheral Devices (03-4)

  6. 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)

  7. 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)

  8. I2C Bus • I2C Bus • Overview • Start and Stop Conditions • Data Transfers • Bus Variants Input/Output Systems and Peripheral Devices (03-4)

  9. 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)

  10. 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)

  11. I2C Bus • I2C Bus • Overview • Start and Stop Conditions • Data Transfers • Bus Variants Input/Output Systems and Peripheral Devices (03-4)

  12. 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)

  13. 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)

  14. 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)

  15. I2C Bus • I2C Bus • Overview • Start and Stop Conditions • Data Transfers • Bus Variants Input/Output Systems and Peripheral Devices (03-4)

  16. 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)

  17. 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)

  18. Serial Buses • Serial Buses • I2C • USB Input/Output Systems and Peripheral Devices (03-4)

  19. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  20. 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)

  21. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  22. 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)

  23. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  24. Bus Topology (1) • Hubs • Functions (devices) Input/Output Systems and Peripheral Devices (03-4)

  25. 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)

  26. 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)

  27. Bus Topology (4) Input/Output Systems and Peripheral Devices (03-4)

  28. 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)

  29. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  30. 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)

  31. 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)

  32. 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)

  33. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  34. 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)

  35. 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)

  36. 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)

  37. 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)

  38. 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)

  39. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  40. 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)

  41. USB • USB • Introduction • Features • Bus Topology • USB Versions • Cables and Connectors • Electrical Interface • Transfer Types Input/Output Systems and Peripheral Devices (03-4)

  42. 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)

  43. 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)

  44. 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)

  45. 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)

  46. 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)

  47. 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)

  48. 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)

  49. 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)

  50. 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)

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