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2nd ADVANCED COURSE ON
DIAGNOSTICS AND DATA ACQUISITION
Instrumentation Buses,
Digital Communication and Protocols
J. Sousa
Summary
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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)
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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
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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
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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
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up to 12 special symbols: start-offrame, end-of-frame, link idle …
Un-allowed symbols permit error
detection
Used among others in:
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PCI Express
IEEE 1394b
Serial ATA
Fibre Channel
Gigabit Ethernet
InfiniBand
Serial RapidIO
HyperTransport
Communication Protocols
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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:
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data corruption
lost data packets
duplicate arrival
out-of-order packet delivery
Instrumentation buses
• Local
• Backplane
• System
• Parallel buses
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GPIB (IEEE 488)
VME
PCI
FPDP
• Serial buses
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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
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AdvancedTCA Data Transport
– Differential signaling capable of 10
Gbps (XAUI) today
– 5+ Gbps differential signal capacity
– Single backplane supports many
fabric technologies and topologies
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Base Interface
– 10/100/1000 BASE-T Ethernet
– Dual Star fabric topology
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Fabric Interface
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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
CODAC Networks
CMD
STATUS /
DATA
TCN Interface
Unit
Interlock
Interface Unit
Plant System Host
EDN Interface
Unit
Real Time
Feedback Data
NTP
Fieldbus
AVN Interface
Unit
Safety Interface
Unit
Video Data
Subsystem
(PLC / PC )
Digitizers
PIS
EVENTS
PSS
Subsystem
Subsystem
Equipment
Equipment
CLOCK
Subsystem
Equipment
Actuators
/ Sensors
Sensors
Subsystem
Digitizers
Equipment
Digitizers
Actuators
/ Sensors
Sensors
Plant System Process
Actuators
Actuators
/ Sensors
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Actuators
Sensors
Actuators
ITER_CODAC_PCDH_Figures_Visio_0011
Interface I&C
SDN Interface
Unit
Plant System
• Plant Operation Network
• Synchronous DataBus
Network
• Event Distribution Network
• Time Communication
Network
• Audio Video Network
• Central Interlock Network
• Central Security Network
I&C Bridge
PON
SDN
EDN
TCN
AVN
CIN
CSN
Networks
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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.
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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
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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
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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