Topic 6 Digital Technique Data buses

Malaysian Inst itute of Aviat ion Technology

Revision 00 Issue 01 Module 5.4

DIGITAL TECH (MECH)AKD 21102

CHAPTER 6

DATA BUSES


• To understand the operation of data buses in aircraft systems, including knowledge of ARINC and other specifications


LEARNING OUTCOME


• A wire or group of wires used to move data to/from components and to/from other computer

• The data can be in the form of electrical pulses or light signals (fiber optics)


DATA BUSES


• Aeronautical Radio INCorporated (ARINC) was established in 1929

• Leading provider of the transport communications and systems and engineering solutions for 5 major industries i.e. aviation, airport, defence, government and transportation.

• Primary activity is to produce specifications and reports for purpose of :– Indicating to manufacturers the group opinion concerning

requisites of new equipment– To channel new equipment design in direction which will result in

maximum standardization


ARINC


• Examples of ARINC specifications are: ARINC 573 : Digital flight data recording ARINC 561 : Inertial navigation systems ARINC 429 : Transfer of digital data

between avionics components ARINC 629 : Improvement of ARINC 429


ARINC


• Is a specification which define how avionic equipment and systems should communicate to each other

• Consist of pairs of twisted wires with shielding• Point to point bus and uses a unidirectional data

bus standard (TX and RX are on separate ports)• Also known as the Mark 33 Digital Information

Transfer System (DITS)


ARINC 429


• Messages are transmitted at either 12.5 kbit/s or 100 kbit/s to other system element that are monitoring the bus messages

• Always transmitting either 32 bit data words or a NULL state


ARINC 429


• Self clocking and self synchronizing system called ‘bipolar return to zero’

• Transmitting in binary bit form where bit ‘1’represent high voltage (+5V) and bit ‘0’ represent low voltage (-5V) level for half of clock cycle then each pulse return to zero in the middle of the clock pulse


ARINC 429: Electrical Characteristics



ARINC 429: Electrical Characteristics


• Only one transmitter on a wire pair• Always transmit 32 bit word or a NULL state• At least 1 receiver on wire pair and up to 20

receivers only• Number of receiver depend on line length and

the number of receivers connected to the bus


ARINC 429 : Protocol


Revision 00 Issue 01 Module 5.4Example of ARINC 429 Application in Boeing 747


• Word format is a 32 bits with 5 basic parts:1) Label2) Source/Destination Identifier (SDI)3) Data field4) Sign Status Matrix (SSM)5) Parity bit (P)


ARINC 429 :Word Format



Malaysian Institute of Aviation Technology

ARINC 429 - Word Format





• LABEL - The first 8 bits of the word (octal coded). Identifies the information contained in the data e.g. airspeed, total air temp.

LABEL PARAMETER

230 True Airspeed

231 Total Air Temperature

233 Static Air Temperature

323 Flight Path Acceleration

330 Body Yaw Rate

Example of label




• SOURCE/DESTINATION IDENTIFIER (SDI)

- used to identify the source/ destination of a word e. g. Which of a number of installations the word is coming from or needs to be directed into.




ARINC 429 - Word Format • DATA FIELD - contains specific data related to

the LABEL. For binary word contained in bits 11- 28 and binary coded decimal (BCD) in bits

11- 29. Any bit not used are filled with logic 0's (pad bits)

• SIGN STATUS MATRIX - bits 29,30,31 for binary word and 30,31 for BCD. Identify characteristics of the word e.g. east/west, +ve/- ve and its status e.g. No computed data, failure warning, functional test or normal operation.




ARINC 429 - Word Format • SSM code for identity characteristic of

the word for BCD data




ARINC 429 - Word Format • SSM code for status of word for BCD data





• PARITY - Uses odd parity e.g. Total number of logic '1' in the word must be an odd number. If not parity bit is set to 1. - Uses to check an error e.g. If receiving signal

doesn't contain odd number 1, fault signal will be generated.


• The least significant bit (LSB) of each byte except the label is transmitted ahead of the data in each case. The order as follows:

8,7,6,5,4,3,2,1,9,10,11,12,13,14,….32


ARINC 429 :Transmission Order


• Additional ARINC standard that is being developed and is used in new fleet of BOEING 777 aircraft

• Uses a high speed bidirectional bus with the capability of either periodic or aperiodic transmission

• Access to the bus is controlled by a sophisticated protocol involving wait period, quiet period and other rules

• Data bus is unshielded twisted pair of wires, bonded and terminated at both ends.

• Data is send at the rate of 2 Mbps


ARINC 629

Topic 6 Digital Technique Data buses

Engineering

Transcript of Topic 6 Digital Technique Data buses