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