Avionics Digital data buses

AVIONICS Digital data buses

Avionics, Lecture, Ivan, 2011 1 w

References

Avionics, Lecture, Ivan, 2011

«ARINC»: www.arinc.com Avionics Systems Standardization Committee: www.era.co.uk/assc Avionics data buses: http://www.interfacebus.com/Design_Connector_Avionics.html

summary

Digital data buses Development of DDB ARING 429 MIL-STD-1553B ARINC 629

Data Bus, DB

Data bus is a subsystem that transfers data between computer components inside a computer or between computers.

Consists of • Wire • Information Packing equipment • algorithms and formats of data

transition

•inside LRU; •Between LRU; •Transmit data from sensors to system; •Between systems.

Do you recall functional integration?

www.OSTROUMOV.co.cc OSTROUMOV IVAN

Distributed analog architecture

1950s, 1960s

Lots of wire, no bus

Very difficult to modify

electro-mechanical parts

heavy, large space, many pieces

Boeing 707, VC10, DC-9, Boeing 737

Distributed digital architecture

Digital systems, heavy, slow, difficult to reprogram (AN/ALQ-162)

Each component contains its own computer and memory

Uses a bus between components (less wire)

Each unit has a dedicated function

Difficult to expand

Boeing 737, 767 A330 (tanker), Tornado, Sea Harrier

Federated digital architecture

Systens communicate via a 1553B bus

Additions are easy, only requires that the bus controller be reprogrammed

Can employ many buses to separate common equipment (ex : EW on the F-18 with its own MC)

Integrated modular architecture

Interchangeable modules can realize diffrent system functions

Permits on-board repairs/swaps, that can automatically reconfigure

Common types of serial digital data transmission are:

Single source-single sink. This is the earliest application and comprises a dedicated link from one piece of equipment to another. This was developed in the 1970s for use on Tornado and Sea Harrier avionics systems.

Common types of serial digital data transmission are: • Single source-multiple sink. This describes a

technique where one piece of transmitting equipment can send data to a number of recipient pieces of equipment (sinks). ARINC 429 is an example of this data bus which is widely used by civil transport and business jets.

Common types of serial digital data transmission are: Multiple source-multiple sink. In this system, multiple

transmitting sources may transmit data to multiple receivers. This is known as a full-duplex system and is widely employed by military users (M1L-STD-1553B) and by the B777 (ARINC 629).

The major digital data buses in widespread use today in avionics are:

ARINC 429 (A429). MIL-STD-1553B, also covered by UK Def Stan 00-

18/Parts 1 and 2 and NATO STANAG 3838. ARINC629 (A629).

SAE Standards

AIR1189 Airborne Internal Interface Standards for Moderate Bit Rate Digital Time Division - Multiplex Systems AIR4013A Multiplex Data Bus Networks for Mil-Std-1760 Stores ARP4258 Application of Low Speed Avionic System Discrete Signal Interfaces AS15531 Digital Time Division Command/Response Multiplex Data Bus AS4075 High Speed Ring Bus (Hsrb) Standard AS4075/1 Optical Implementation Relating to the High Speed Ring Bus (Hsrb) Standard AS4710 Pi-Bus AS5370 Multi-Transmitter Bidirectional Fiber-Optic Data Bus for Distributed Aircraft Control Systems AS5643 IEEE-1394b Interface Requirements for Military and Aerospace Vehicle Applications

ARINC standards

ARINC 429. Digital Information Transfer System. Point-to-point, 2-wire Bi-Polar Return-to-Zero signal. 32 bit data. 100K or 12.5K bit rate. ARINC 629. Multi-Transmitter Data Bus. Serial data bus which operates over cable at 2Mbps. Developed by Boeing. ARINC 659. Backplane Data Bus for IMA, operates at 60Mbps as a commercial aviation bus. ARINC 818. released in Jan. 07, is a video interface and protocol standard developed for high bandwidth, low latency, uncompressed digital video transmission.

IEEE standarts

IEEE-std-1393 Spaceborne Fiber Optic Data Bus (SFODB); 1 Gb/s, fiber. Std 1149.5 Standard for Module Test and Maintenance Bus (MTM-Bus) Protocol. IEEE 1355 SpaceWire, based on the HIC (IEEE-1355) bus, and Low Voltage Differential Signaling.

Other buses include:

Avionics Standard Communications Bus (ASCB), available in several forms and based upon Ethernet protocols. ASCB was developed by Honeywell and is used in General Aviation (GA) and business jet applications.

Commercial Standard Data Bus (CSDB) developed by Rockwell Collins for use in GA applications.

Avionics Full Duplex Ethernet (AFDX) based upon commercial Fast Switched Ethernet (FDX) technology and adopted for the Airbus A380.

In some applications, commercial RS 232 and RS 422 buses are also used.

Comparative DDB transmission rate

ARING 429 20

Key attributes

Simplex broadcast bus

Bit rates:

'High Speed' 100kbps

'Low Speed' 12 to 14.5kbps

Encoding: return to zero bipolar tri-state modulation

Message length: 32 bit word, 255 word data block in block transfer mode

Media access: simplex single source multiple sink plus full duplex

Topology: single source multiple sink either star or bus

Number of nodes: 20 sinks, 1 source

The ARINC 429 specification defines the requirements for a data transmission system based on the use of a single data source and reception of that data by up to 20 sinks or receivers. The maximum number of receivers permitted for connection to a source is limited by the specified minimum receiver input impedance.

«Star» topology

Bus drop topology

Multiplex topology

Full duplex link

Return to Zero Bipolar Tri-state Modulation

The signal has three states 'HI', 'NULL' and 'LO' represented by the differential voltage between the two wires of the cable.

A logical ‘1’ is signalled by transmission of a +10 ±1V pulse followed by a 0±0.5V null period.

A logical ‘0’ is signalled by transmission of a –10 ±1V pulse also followed by a 0 ±0.5V null period.

Two ranges of transmission rate are defined. 'High Speed' at 100 kbps ±1% and 'Low Speed' in the range 12 to 14.5 kbps.

Word format

ARINC 429 organizes data in 32 bit words. typical ARINC 429 word consisting of five parts:

• Label • Source/Destination Identifier (SDI) • Data field • Sign/Status Matrix (SSM) • Parity bit

ARINC 429 Word Format

Label (data name)(1-8)

each sink is required to inspect the Label field which is encoded in octal to represent the type of information contained within the 32-bit word.

Each data item is assigned a label code listed in the ARINC 429 specification and each source may have up to 255 Labels, assigned for its use.

Source/ Destination Identifier (SDI)

The SDI field contains just two bits. The SDI’s functions are to: indicate the intended destination of the data on

a multi-sink bus identify the source of the data on a multi-source

bus (multi-system installation) to add an extension to the Label, in which case

receiving systems decode the Label/SDI combination.

Data formats

two’s complement binary data BCD (2/10) data Discrete bits Maintenance data special Alphabet (Symbol and numeric)

Sign/Status Matrix (SSM)

It may be used to indicate sign information e.g. +, -, compass direction etc. Each Label has its own unique implementation of the SSM Sign function.

The SSM field may also be used to indicate the source equipment status, operational mode or data validity.

Parity

The parity bit is set to impose odd parity on the word.

If even – mistake!!!!!

MIL-STD-1553B 38

Key attributes

Serial time division command response data bus Bit rate: 1Mbps Encoding: baseband Manchester II bi-phase level Message length: 1 to 32 16-bit words

Структура MIL-STD-1553B

A typical example

Note that a module can be both a bus controller and a remote terminal

Кодування кодом «Манчестер ІІ»

Manchester Encoding

Manchester on a twisted pair

Subtractor

Signal

MIL-STD-1553B formats

The standard defines three word formats all words are 20 bit times long The Command Word is issued only by a bus

controller and is used to convey commands to RTs.

CW (Bit times)

1 – 3 are used for an invalid Manchester synchronising pattern.

4 – 8 contain the address of the RT that is to act on the command (‘11111’ indicates a broadcast command).

9 - the T/R bit, indicates to the receiving RT whether it is to transmit (T/R = 1) or receive (T/R = 0) data words in response to the command.

CW (Bit times)

10 – 14, if set to ‘00000’ or ‘11111’, indicate that the next 5 bits are to be interpreted as a mode code. If set to any other value they indicate a subaddress within the subsystem served by the RT that is to source or receive data.

15 – 16 indicate either a mode code that requires the RT to perform some control function (e.g. Reset, Initiate Self Test etc.) or the number of Data Words to be either received or transmitted by the RT.

Bit 20 is a parity bit set for odd parity over the previous 16 bits.

Data Words

Data Words may be transmitted either by the BC or RT.

Bits 1 – 3 are used for an invalid Manchester synchronising pattern.

Bits 4 – 19 contain the data to be conveyed. Bit 20 is the parity bit.

Status Words

Status Words are transmitted only by RTs and are used to indicate to the BC the state of the RT and the RT’s view of recent events on the bus. For example, certain status bits are used to indicate whether there is a fault in the subsystem or terminal and others the results of error checking, broadcast message reception and service request (latent interrupt) conditions.

Status Words

Bit times 1 – 3 are used for an invalid Manchester synchronising pattern.

Bits 4 – 8 contain the address of the RT transmitting the Status word.

Bits 9 – 11 and 15 – 19 are the status bits and bits 12 – 14 are reserved and unused (always ‘0’).

Data Transfer Message Formats

Принцип передачі даних MIL-STD-1553B

Broadcast Message Formats

Передача даних у широкомовному режимі

ARINC 629 56

Key attributes

ARINC specification 629 Multi-transmitter Data Bus Serial data bus with distributed media access. Bit rate: 2Mbps. Encoding: Manchester II bi-phase. Message length: up to 31 Word Strings each

containing one 16 bit label word and up to two hundred and fifty-six 16 bit data words

Number of nodes: up to 120.

ARINC 629 topology

ARINC 629 Message Structure

Basic Protocol – Periodic Mode

Передача повідомлень у ARINC 629

Avionics Digital data buses

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