EASA PART-66 MODULE 5.4 : DATA BUSES
- 1. 5.4 DATA BUSES www.part66.blogspot.com 1
- 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. 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. 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. 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. 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. 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
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- 9. DATA TRANSMISSION 9
- 10. ARINC DATA WORD 1- 8 Label – information about the data 9-10 SDI – Source Destination Information 11-28 – Data 29-31 – SSM Sign Status Matrix 32 – Parity bit - sum of all logic is ODD 10
- 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. 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. 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. INSTALLATION 14
- 15. 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 15
- 16. Triple-Triple Redundant 777 Primary Flight Computer 16
- 17. Time Division Multiplex Linear Bus Multiple Transmitter Access 2 Mbps Data Rate Current Mode Coupling (Present implementation) 17
- 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. ARINC 629 SYSTEM - COMPONENTS 19
- 20. ARINC 629 DATA BUS CABLE 20
- 21. ARINC 629 BUS 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. 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. 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. MESSAGE STRUCTURE 24