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2 nd ADVANCED COURSE ON DIAGNOSTICS AND DATA ACQUISITION

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  1. 2nd ADVANCED COURSE ON DIAGNOSTICS AND DATA ACQUISITION Instrumentation Buses, Digital Communication and Protocols J. Sousa

  2. Summary • Digital Communication • Signalling, Encoding and Protocols • Instrumentations Buses • Networks for Control and Data Acquisition

  3. Digital Communication

  4. Types of data transmission • Parallel • Theoretically higher transfer rates • Short distances • Volumous cabling • Serial • Longer distances • Complex channel encoding and data recovery • Synchronous or Asynchronous • Hybrid transmission • Bundle of serial links • Long distances and high transfer rates • X1, X2, X4, X16, X32

  5. Asynchronous transmission (RS-232C) • Each word is enclosed between two synchronization characters (start and stop bit). • The start bit indicates a word follows. The data line is held in mark or “1” when no data is being transmitted; set to space or “0” by the start bit. The receiver synchronizes its clock with the start bit • The stop bit reports word transmission complete resetting data line to “1”. • Parity bit. • Odd parity: “1” if checksum is odd number • Even parity: “1” if checksum is even number

  6. Synchronous transmission • Parallel or serial transmission • No start and stop bits • A continual stream of data is then sent between the two nodes • A timing signal (character) is generated periodically by the transmitter. • Receiver clock is re-synchronized by the timing signal. • Synchronous clocks in both transmitter and receiver allow data recovery. • Error detection and correction

  7. Signal distorsion on transmission channel • Serial data transmission sends binary bits of information as a series of optical or electrical pulses • The transmission channel (cable, radio, fiber) generally distorts the signal in various ways • Jitter on reception can impede correct data reception

  8. Source encoding – 8b/10b • 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to: • achieve DC-balance • provide enough state changes to allow reasonable clock recovery • up to 12 special symbols: start-of-frame, end-of-frame, link idle … • Un-allowed symbols permit error detection • Used among others in: • PCI Express • IEEE 1394b • Serial ATA • Fibre Channel • Gigabit Ethernet • InfiniBand • Serial RapidIO • HyperTransport

  9. Communication Protocols • Detection of the underlying physical connection (wired or wireless), or the existence of the other endpoint or node • Handshaking • Negotiation of various connection characteristics • How to start and end a message • How to format a message • What to do with corrupted or improperly formatted messages (error correction) • How to detect unexpected loss of the connection, and what to do next • Termination of the session and or connection.

  10. Internet Protocol (IP) • Deliver datagrams (packets) from the source host to the destination host based on their addresses • Defines addressing methods and structures for datagram encapsulation • Connection-less protocol • Lack of reliability allows any of the following fault events to occur: • data corruption • lost data packets • duplicate arrival • out-of-order packet delivery

  11. Instrumentation buses • Local • Backplane • System • Parallel buses • GPIB (IEEE 488) • VME • PCI • FPDP • Serial buses • RS-232C • USB • PCI Express • Ethernet (IEEE 802)

  12. Peripheral Component Interconnect (PCI) • Parallel, Synchronous • 32/64-bit, 33/66 MHz • Max data throughput rate from 133 to 266 Mbyte/s • PCI-X, PCIe physical share logical PCI specification

  13. PCI Express (PCIe) • Serial, point-to-point type interconnect for communication between two devices • PCI Express interconnect consists of either a x1, x2, x4, x8, x12, x16 or x32 point-to-point Link • A Lane consists of signal pairs in each direction. • A x1 Link consists of 1 Lane or 1 differential signal pair in each direction for a total of 4 signals. • Switch-based technology • Packet Based Protocol; 8b/10b coding. • 2.5 Gbits/sec/lane/direction transfer rate (~200MB/lane). 3.2GB on x16

  14. VME • VMEbus: VERSAmodule Eurocard bus • Parallel, Asynchronous • 64-bit bus in 6U-sized cards and 32-bit in 3U cards. • VME64 has a typical performance of 40 MB/s.

  15. GPIB • Connect and control programmable instruments • IEEE-488 allows up to 15 devices by daisy chaining connections • 8-bit parallel, asynchronous electrical bus • maximum data rate is 1 MB/s to 8 MB/s

  16. AdvancedTCA • AdvancedTCA Data Transport • Differential signaling capable of 10 Gbps (XAUI) today • 5+ Gbps differential signal capacity • Single backplane supports many fabric technologies and topologies • Base Interface • 10/100/1000 BASE-T Ethernet • Dual Star fabric topology • Fabric Interface • SERDES (3.125 Gbps minimum) • 1x, 2x, or 4x Channels • Star or Mesh fabric topology • actual throughput capacity of ~800 MByte/s per link • Synchronization Interface • Three dedicated clock interfaces (8kHz, 19.44 MHz, user defined) • Redundant buses

  17. Networks for Control and Data Acquisition • Plant Operation Network • Synchronous DataBus Network • Event Distribution Network • Time Communication Network • Audio Video Network • Central Interlock Network • Central Security Network

  18. Networks • Synchronous DataBus Network (SDN) • SDN is used for deterministic communication between CODAC systems and Plant Systems, which cannot be guaranteed with conventional technology as used by PON. • The purpose of SDN is to provide data exchange between multiple Plant Systems and CODAC systems for plasma feedback control with a performance cycle time on less than 1 ms. • Time Communication Network (TCN) • The purpose of TCN is to provide the distribution of timing information to plant wide I&C for synchronization and time stamping to processes, data, and actions/events. • TCN interface allows to generate synchronized clock from timing information with guaranteed phase alignment and jitter. • Standards like UTC, GPS, NTP, IEEE 1588 • Event Distribution Network (EDN) • The Event Distribution Network (EDN) manages the events signaling among CODAC Systems and Plant Systems with a lower latency than the Synchronous DataBus. • Low latency, low jitter • Audio Video Network (AVN) • The purpose of the AVN is to provide plant wide distribution of surveillance audio-video signals and diagnostics video data. • AVN interfaces standard source devices like camera, mic etc. and standard receiving devices like screens, TV, remote displays