2nd 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, 19.44 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

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Video Data

I&C Bridge

NTP

Actuators Actuators

Equipment

Subsystem

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TCN InterfaceUnit

Equipment

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SDN

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EDNTCN

CSN

PON

SDN InterfaceUnit

Plant System Host

CLOCK

CODAC Networks

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Digitizers

Digitizers

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EquipmentEquipment

Subsystem Subsystem

Subsystem (PLC / PC )

Actuators / Sensors

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EDN InterfaceUnit

AVN InterfaceUnit

Safety InterfaceUnit

Interlock Interface Unit

Plant System Process

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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