Slide for student who want to take EASA part66 exam Other note you can get at http://part66.blogspot.com

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

8. 8

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