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

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

Digital Communication

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

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

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

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

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

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.

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

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

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

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

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.

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

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, MHz, user defined) – Redundant buses

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

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