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# EASA PART-66 MODULE 5.4 : DATA BUSES

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### EASA PART-66 MODULE 5.4 : DATA BUSES

1. 1. 5.4 DATA BUSES www.part66.blogspot.com 1
2. 2. BITS, BYTES,WORD• The traditional data hierarchy are: – Bit – either 0 or 1 – Bytes – a collection of bits to make a character – Word – a collection of bytes to have a meaningful word. – Field – a collection of words – A record – a collections of field on a related subject. 2
3. 3. Traditional Example – STUDENTS FILE• Student’s File – consist of 100 records of student.• A record – for example – information on a student.• Fields – example students name or address or telephone number e.g Abraham Maslow• Word – the name of a student e.g Abraham• Bytes – e.g A is represented by 10000001• Bit – either 0 or 1 3
4. 4. ARINC 429 DATA WORD• In computing, word is the natural unit of data used by a particular processor design.• It is basically a fixed sized group of bits that are handled as a unit by the instruction• The number of bits in a word (the word size, word width, or word length) is determined by the computer architecture. 4
5. 5. INTRODUCTION TO DATA BUSES• Data buses are used to transmit data from one component to another.• The buses can be electrical or fibre optic.• The specification for data transmission is drawn by ARINC.• The standard used in aircrafts is the ARINC 429. 5
6. 6. ABOUT ARINC 429• It defines how avionics equipment should talk with each other.• Defines the electrical and data characteristics and protocol.• A 32 bits serial bus with data flow in one direction. If two directions are required, then two sets of buses are required. (max 20 receivers)• The signal uses three level -10v, 0 and +10v. (measured between 2 wires)• High speed 100k and low speed of 12-14k/sec (cannot be mixed) 6
7. 7. ARINC 429 DATA WORD• Five Basic Parts – Label (e.g True air speed, TAT) – Source /Destination Identifier (SDI) – Data Field (bit 11-28) – Sign Status Matrix (SSM) (e.g +, - , North) – Parity Bit ( Odd parity) 7
8. 8. 8
9. 9. DATA TRANSMISSION 9
10. 10. ARINC DATA WORD1- 8 Label – information about the data9-10 SDI – Source Destination Information11-28 – Data29-31 – SSM Sign Status Matrix32 – Parity bit - sum of all logic is ODD 10
11. 11. DATA FORMAT• It is using Bipolar return to zero (RZ) modulation. – The data in 3 states, hi, null, lo (1, null, 0) – A 4 null period separate the words. 11
12. 12. DATA BUS• Operates on one of the two speeds – High - 100kbits/sec – Low - 12.0kbits/sec• Self clocking – the receiver receives the null between the bits to generate its internal clock.• Self synchronous – the 4 bits null is recognized and used to generate word synchronisation. 12
13. 13. VOLTAGE LEVEL• The voltage used is +10 , 0 and -10 volts.• +10volts signifies logic 1 and (-10v) is logic 0 (obsolute voltage +- 5 )• The second half of the bit is always null.• The shield is grounded at both end of he wire. 13
14. 14. INSTALLATION 14
15. 15. 1977 => Boeing began to work on “DATAC” project1977 - 85 => DATAC Emerged as ARINC 6291989 => ARINC 629 was adopted by AEEC1990 => ARINC 629 was first implemented in BOEING-777 15
16. 16. Triple-Triple Redundant777 Primary Flight Computer 16
17. 17. Time Division MultiplexLinear BusMultiple Transmitter Access2 Mbps Data RateCurrent Mode Coupling(Present implementation) 17
18. 18. ARINC 629• ARINC 629 introduced in May 1995• Used on B777, A330 andA340 .• Multiple-source, multiple sink system• Each terminal can transmit receive data• ARINC 629 can handle total of 120 terminals• It supports a data rate of 2 Mbps 18
19. 19. ARINC 629 SYSTEM - COMPONENTS 19
20. 20. ARINC 629 DATA BUS CABLE 20
21. 21. ARINC 629BUS INSTALLATION BUS COUPLER• Most of the wires are in • The coupler is used to electronics compartment. connect the LRU to the data This to enable the black bus. boxes to talk to each other. • A maximum of 120 couplers can be connected. 21
22. 22. 429 V 629 BUSES• A pair if wire per link • Shared buses – max 120• One way flow • Two ways• Max 100kb • Max 2 mega• Receiver max 20 • Receiver – max 120 22
23. 23. ARINC 629 MESSAGE STRUCTURE Message Max 31 word string / gap 4 bits Each word string Label + 256 datawords Each label Each data word 20bits/label-12/ext-4/3 syncro/1 parity 20bits/ 16 data/ 3 syn/ 1 parity 23
24. 24. MESSAGE STRUCTURE 24