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Digital Avionics
Avionics Data Bus ( CP – 4)
Avionics BUS system
Bus : contraction of Greek word “ OMNBUS “ means “ to all “ Hence associated with “ Protocol” for data interchange in digital systems
# It provides a medium for the exchange of data and information between various Avionics subsystems
# Integration of Avionics subsystems in military or civil aircraft and spacecraft.
DATA BUS
set of formal rules and conventions governing the flow of information among the systemsLow level protocols define the electrical and physical standardsHigh level protocols deal with the data formatting, including the syntax of messages and its format
PROTOCOL
Avionics Bus
Bus
Serial
Synchronous Asynchronous
Parallel
BUS SELECTION CRITERION
STANDARD BUS SYSTEM
COTS & Commercial a. RS 232 C ( Serial Asynchronous , Twisted cable type )
--- RS 422 differential Signals --- RS 485 More devices can be connected
b. Parallel Interface c. USB / FireWire d. Ethernet ( ISO /IEC 802.3 )
MILITARY BUSa. Tornado Serial Bus b. ARINC 429c. Mil STD 1553 Bd. STANAG 3910
Advanced Bus systema. CSDB ( Commercial System Data Bus )b. Optical Fibre data bus c. Global Bus ( using Time Triggered Protocol
Token Passing Bus architecture
Ethernet Protocol/BusDeveloped by XEROX PARC 1970. adopted as std in 1978.Stds :IEEE 802.3 : CSMA/CD Ethernet 2 Mbps IEEE 802.3 U ; “ 100 Mbps z : 1 Gbps ------------------------------------------------------------------------------Topology Shared access system : Bus , Ring ( token Ring ) , Star Media Access control ( MAC ) Mechanism : - CSMA / CD ( Broadcast Technology : when sensed collision stop sending ){ each data frame separated by 9.6 μs – to switch from send to receive:}-------------------------------------------------------------------------------------Other IEEE Stds based on same concept :IEEE 802 .11 WLANIEEE 802.15 BluetoothIEEE 802.16 Wi MAx
Ethernet Data Format
Preamble 64 bits
Source add 48
Dest.Add 48 Type Data
1500 CRC 32
Preamble : sequence of 7 bytes 10101010. : synchronizationData : 1500 bytes
Comparing Data bus capability
BUS Architecture
BUS CONTROLLER (BC)
REMOTE TERMINAL (RT)
MONITORING TERMINAL (MT)
TRANSMISSION MEDIA
Developed at Wright Patterson Air Force
Base in 1970s
Published First Version 1553A in 1975
Introduced in service on F-15 Program
Published Second version 1553B in 1978
History : 1553 B
MIL-STD-1553 : Command / Response : Time Division Multiplex Data Bus,
the method of communication and the electrical interface requirements for the subsystems
connected in the data bus
MIL STD 1553 B
MIL STD 1773 B : Fibre Optic Data bus
Data Rate
Message Length
Data Bits per Word
Transmission Technique
Encoding
Protocol
1 Mbps
32 Word Strings(maximum)16 Bits
Half - Duplex
Manchester II Bi-phase
Transmission Mode
Word Length 20 Bits
Voltage Mode
Command Response
Message Sequencing ( 9 Types)
ARINC : Aeronautical Radio Incorporated
Standards
ARINC 429 : Serial Data Bus standard
ARINC 615 : software Protocol ( high speed read / write )
ARINC 629 : 2 Mbps Bi directional standard
ARINC 708 : From Weather Radar to aircraft display data transfer std
ARINC 717 : Flight Data Recorder standard
ARINC : Aeronautical Radio Inc. funded by airlines, in charge of the definition of Aeronautical standards that ensure interchange ability and interoperability. AEEC : Airlines Electronic Engineering Commitee ADN : Aircraft Data Network working group
Unidirectional , can take on 20 receivers of data on a single bus .
Packets of 32 bits Bit Rate 12.5 Kbps to 100 Kbps Voltage Level + /- 5 v Data encoding Bi Polar return to Zero Uses labeling of data to differentiate bet different data types
Contd…
ARINC 429 Data Packet
1-8
bits
Label 9-10SDI 11
-29
Data 30-3
1
SSM 32Parity
Label : identifies what type of data e.g altitude . Airspeed etcSDI : receivers are assigned ID code SSM : specifies field such as North , south , + or –P : Parity
Impedance Matching
Bus couplers : Voltage Mode Current mode operation
ARINC 429RECEIVER
ARINC 429RECEIVER
ARINC 429RECEIVER
ARINC 429 DATABUS UPTO 20 RECEIVERSTOTAL
ARINC 429TRANSMITTER
ARINC 429 is a differential line with bipolar non return to zero (BNRZ) signaling. Differential voltage between two lines is +10V (between 7,25 and 11V), 10V (between -7,25 and -11V) or 0 V (between -0,5 and 0,5V) for high, low and null respectively.
32 bit words are separated with 4 bit times of null gaps and each bit has a transition from the zero volts according to BNRZ which together help in synchronization without clock
Binary Data allocation : sign bit 1 ( Left , from , Below, South , West ) Sign bit 0 : ( North East , right, to , over)
1977 => Boeing began to work on “DATAC” project
1977 - 85 => DATAC Emerged as ARINC 629
1989 => ARINC 629 was adopted by AEEC
1990 => ARINC 629 was first implemented in BOEING-777
ARINC 629 data : Time Division Multiplex Linear Bus Multiple Transmitter Access 2 Mbps Data Rate Current Mode Coupling
(Present implementation)
Data Rate
Message Length
Data Bits per Word
Transmission Technique
Encoding
Protocol
Transmission Mode
Word Length
2 Mbps
31 Word Strings(maximum)
16 Bits
Half - Duplex
Manchester II Bi-phase
Carrier Sense Multiple AccessCollision avoidance
Voltage Mode,Current Mode, Fiber Optic Mode
20 Bits
Specifications
ARINC 629TERMINAL
ARINC 629TERMINAL
ARINC 629TERMINAL
ARINC 629 DATABUSUPTO 120 SUBSCRIBERTERMINALS