1. Introduction Electrical Considerations Data Transfer Synchronization Bus Arbitration VME Bus Local Buses PCI Bus PCI Bus Variants Serial Buses 11/06/20141Input/Output Systems and Peripheral Devices (03-4)

2. Serial Buses I 2 C Bus USB 11/06/20142Input/Output Systems and Peripheral Devices (03-4)

3. Viable alternatives to parallel buses Advantages: Smaller connectors Reduced susceptibility to electrical interferences Longer interconnection distance Higher reliability Lower cost of the interface 11/06/20143Input/Output Systems and Peripheral Devices (03-4)

4. Serial Buses I 2 C Bus USB 11/06/20144Input/Output Systems and Peripheral Devices (03-4)

5. I 2 C Bus Overview Start and Stop Conditions Data Transfers Bus Variants 11/06/20145Input/Output Systems and Peripheral Devices (03-4)

6. I 2 C (Inter-Integrated Circuits) – Philips Bidirectional bus with two wires: SDA (Serial Data) SCL (Serial Clock) 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 6

7. A device connected to the I 2 C 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 11/06/20147Input/Output Systems and Peripheral Devices (03-4)

8. I 2 C Bus Overview Start and Stop Conditions Data Transfers Bus Variants 11/06/20148Input/Output Systems and Peripheral Devices (03-4)

9. 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 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 9

10. Data on the SDA line must be stable while SCL is logical 1 Data can be changed only when SCL is logical 0 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 10

11. I 2 C Bus Overview Start and Stop Conditions Data Transfers Bus Variants 11/06/201411Input/Output Systems and Peripheral Devices (03-4)

12. Categories of information sent on the I 2 C bus: Start bit Slave device address (7 or 10 bits) Read/write bit Data bits (segments of 8 bits each) Acknowledge bit (after each data segment) Stop bit 11/06/201412Input/Output Systems and Peripheral Devices (03-4)

13. Example transfer The number of bytes in a transfer is not restricted The receiver can force the transmitter into a wait state 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 13

14. 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 11/06/201414Input/Output Systems and Peripheral Devices (03-4)

15. I 2 C Bus Overview Start and Stop Conditions Data Transfers Bus Variants 11/06/201415Input/Output Systems and Peripheral Devices (03-4)

16. Original I 2 C 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 11/06/201416Input/Output Systems and Peripheral Devices (03-4)

17. 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 11/06/201417Input/Output Systems and Peripheral Devices (03-4)

18. Serial Buses I 2 C USB 11/06/201418Input/Output Systems and Peripheral Devices (03-4)

19. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201419Input/Output Systems and Peripheral Devices (03-4)

20. USB – Universal Serial Bus Developed in 1995 by a group of companies: HP, Compaq, Intel, Lucent, Microsoft, NEC USB Implementers Forum (www.usb.org)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 11/06/201420Input/Output Systems and Peripheral Devices (03-4)

21. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201421Input/Output Systems and Peripheral Devices (03-4)

22. 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 11/06/201422Input/Output Systems and Peripheral Devices (03-4)

23. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201423Input/Output Systems and Peripheral Devices (03-4)

24. Hubs Functions (devices) 11/06/201424Input/Output Systems and Peripheral Devices (03-4)

25. 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 11/06/201425Input/Output Systems and Peripheral Devices (03-4)

26. Upstream port (for host) Downstream ports (for functions) Cascaded connection up to 5 levels 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 26

27. 11/06/201427Input/Output Systems and Peripheral Devices (03-4)

28. 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 Configuring a function: allocating bandwidth and selecting configuration options 11/06/201428Input/Output Systems and Peripheral Devices (03-4)

29. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201429Input/Output Systems and Peripheral Devices (03-4)

30. 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 11/06/201430Input/Output Systems and Peripheral Devices (03-4)

31. 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 11/06/201431Input/Output Systems and Peripheral Devices (03-4)

32. 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) 11/06/201432Input/Output Systems and Peripheral Devices (03-4)

33. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201433Input/Output Systems and Peripheral Devices (03-4)

34. Differential signals on the D+ and D- wires Supply voltage for peripherals on the V BUS wire Terminations at each end of the cable Provide correct voltage levels for peripherals Allow detection of attach and detach of device s Differentiate between full- and low-speed devices 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 34

35. 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 11/06/201435Input/Output Systems and Peripheral Devices (03-4)

36. 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 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 36

37. 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 11/06/2014 Input/Output Systems and Peripheral Devices (03-4) 37

38. 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 11/06/201438Input/Output Systems and Peripheral Devices (03-4)

39. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201439Input/Output Systems and Peripheral Devices (03-4)

40. 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 11/06/201440Input/Output Systems and Peripheral Devices (03-4)

41. USB Introduction Features Bus Topology USB Versions Cables and Connectors Electrical Interface Transfer Types 11/06/201441Input/Output Systems and Peripheral Devices (03-4)

42. 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 11/06/201442Input/Output Systems and Peripheral Devices (03-4)

43. 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 11/06/201443Input/Output Systems and Peripheral Devices (03-4)

44. 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 11/06/201444Input/Output Systems and Peripheral Devices (03-4)

45. 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 11/06/201445Input/Output Systems and Peripheral Devices (03-4)

46. Serial buses have several advantages compared to parallel buses The I 2 C 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 11/06/201446Input/Output Systems and Peripheral Devices (03-4)

47. 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 11/06/201447Input/Output Systems and Peripheral Devices (03-4)

48. 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 11/06/201448Input/Output Systems and Peripheral Devices (03-4)

49. Advantages of serial buses Overview of I 2 C bus Start and stop conditions Data transfers on the I 2 C bus I 2 C bus variants Features of USB USB hubs USB functions 11/06/201449Input/Output Systems and Peripheral Devices (03-4)

50. 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 11/06/201450Input/Output Systems and Peripheral Devices (03-4)

51. 1.What are the advantages of serial buses? 2.What are the main features of the USB bus? 3.How can a USB host determine the capabilities and resources needed by a USB function? 4.What is the difference between isochronous and asynchronous transfers? 11/06/201451Input/Output Systems and Peripheral Devices (03-4)