Data Buses and Electric Power in Aircraft Systems

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Questions and Answers

What voltage range represents a binary 0 in practical digital systems?

0 to 0.8 V (correct)

0.8 to 2 V

5 to 10 V

2 to 5 V

What primarily ensures synchronization between a transmitter and receiver in digital systems?

Data acquisition

Clock pulse (correct)

Data encoding

Voltage levels

What is a primary advantage of serial data transfer over parallel data transfer?

More complex circuitry

Reduced hardware requirements (correct)

Higher speed

Greater data integrity

How does a receiver process data in serial data transfer?

Processing data sequentially as it arrives Signup and view all the answers

What voltage range is required to represent a binary 1 in practical digital systems?

2 to 5 V Signup and view all the answers

What characterizes analogue data voltages compared to digital data voltages?

They must be exact to avoid errors. Signup and view all the answers

What describes the method of transferring data in serial data transfer systems?

Bits transferred one after another over the same line Signup and view all the answers

For what type of data transmission is serial communication particularly advantageous?

Long-distance communication Signup and view all the answers

What is the primary function of the Bus Controller (BC) in a data bus system?

To issue commands and manage data transfers on the bus Signup and view all the answers

Which of the following components typically contains the Bus Controller functionality?

Flight Management Computer Signup and view all the answers

How does the Bus Controller communicate with remote terminals?

By issuing digital commands that request specific data Signup and view all the answers

What type of commands does the Bus Controller issue to manage the data bus?

Mode commands for control and management of the bus Signup and view all the answers

What happens when the Bus Controller sends a command to a remote terminal?

The remote terminal responds with the requested data after processing Signup and view all the answers

What type of data is primarily transmitted by the Bus Controller?

Binary data representing various aircraft parameters Signup and view all the answers

What is a characteristic of data transmission controlled by the Bus Controller?

Strictly regulates the type of words transmitted across the bus Signup and view all the answers

What role does the Electronic Flight Instrument System (EFIS) play in relation to the Bus Controller?

It displays the digitized information provided by the Bus Controller Signup and view all the answers

What is the primary format used for transmitting ARINC data?

32-bit words Signup and view all the answers

Which of the following is NOT a data type used in ARINC 429?

Hexadecimal Representation Signup and view all the answers

In ARINC 429, what is the significance of the label within a data word?

It identifies the data type and associated parameters. Signup and view all the answers

What role does the Sign/Status Matrix (SSM) play in ARINC 429?

It conveys information about data sign and status. Signup and view all the answers

How are labels typically represented in ARINC 429?

As octal numbers Signup and view all the answers

Which entity incorporated ASCII code into ARINC 429?

ARINC itself Signup and view all the answers

What is the communication method used in ARINC 429 for transmitting information between avionics system elements?

Single twisted and shielded pair of wires Signup and view all the answers

What does the ISO No. 5 standard facilitate in ARINC 429?

It encodes alphanumeric inputs into binary numbers. Signup and view all the answers

What is the primary function of the stub cables in the ARINC 629 system?

To facilitate bidirectional data movement and supply power to current-mode couplers Signup and view all the answers

How many parts comprise the personality data for an LRU?

Two parts: Transmit personality PROM and Receive personality PROM Signup and view all the answers

What is the value of the termination resistors at each end of the ARINC 629 bus cable?

130 Ω Signup and view all the answers

What components make up a message in the ARINC 629 message structure?

A group of word strings each starting with a label word followed by data words Signup and view all the answers

What is the maximum number of word strings that a message can contain in the ARINC 629 system?

31 word strings Signup and view all the answers

What separates messages in the ARINC 629 message structure?

A Terminal Gap (TG) Signup and view all the answers

Which of the following describes the structure of a word string in the ARINC 629 system?

Begins with a label word and contains up to 256 data words Signup and view all the answers

What material covers the foam layer of the cable structure mentioned for the bus cable?

Teflon Signup and view all the answers

What is the primary reason for standardization in avionics equipment manufacturing?

To ensure compatibility across various aircraft models Signup and view all the answers

How many maximum receivers can be connected to an ARINC 429 bus?

20 Signup and view all the answers

What characteristic distinguishes ARINC 429 from the 1553 standard?

It is a simplex data bus Signup and view all the answers

What does the 'simplex data bus' in ARINC 429 imply about data transmission?

Data can only be transmitted in one direction Signup and view all the answers

Which of the following encoding techniques is used by ARINC 429?

Bipolar return to zero Signup and view all the answers

What is the impact of ARINC 429 on manufacturers of avionics components?

Manufacturers can produce standardized components for various aircraft Signup and view all the answers

Which of the following statements about ARINC 429 is true?

It operates within a speed range of 12 to 100 kb Signup and view all the answers

What could be a major disadvantage if different air carriers utilize their own data buses?

Reduced compatibility between different aircraft models Signup and view all the answers

What is the main advantage of small analogue sensors incorporating a microprocessor?

They provide a digital output, removing the need for A/D and D/A converters. Signup and view all the answers

What has been noted about the contemporary status of the MIL-STD-1553 standard?

It is considered outdated compared to modern digital avionics installations. Signup and view all the answers

Which statement regarding MIL-STD-1773 is true?

It repeats the requirements of MIL-STD-1553 nearly word-for-word. Signup and view all the answers

How does the data error rate requirement of fibre optic systems compare to that of wire conductors?

It is unchanged and remains consistent with wire conductors. Signup and view all the answers

In terms of environmental considerations, what is true for fibre optic systems?

Altitude, humidity, temperature, and age affect fibre optics differently than wire conductors. Signup and view all the answers

What is a key difference in the definition of pulses between MIL-STD-1553 and MIL-STD-1773?

Pulses are defined as changes between off and on for fibre optics. Signup and view all the answers

What is one function of Aeronautical Radio Inc. (ARINC)?

Ensuring the efficiency and operation of aviation and travel industry systems. Signup and view all the answers

What common feature do MIL-STD-1553 and MIL-STD-1773 share?

Both maintain identical data encoding and word formats, with minor differences. Signup and view all the answers

Study Notes

Data Buses (5.4)

Learning Objectives:
- Describe the operation of data buses in aircraft systems (Level 2)
- Describe the properties of data bus communication protocols, including: MIL-STD 1553, ARINC 429, ARINC 629, Ethernet, AFDX (Level 2)

Electric Power

Electricity is transmitted over heavily constructed power lines to carry high voltage and current.
Power plants generate electricity.
Transmission lines carry electricity long distances.
Distribution lines carry electricity to homes.
Transformers step up voltage for transmission/step down voltage before entering homes.
Different applications require different amounts of power, affecting the wiring required.
Examples include navigation lights (low current, 28V DC) and aircraft starter motors (high current).

Battery Connected to Aircraft Starter

Aircraft applications use electricity (significant current flow).
Appropriate wiring (sized appropriately) is needed.

Electrical Data Transmission

Electricity is an ideal medium for transmitting information at the speed of light.
Data lines carry minimal current to switch transistors on/off.
Data bus lines are small gauge.
The signal is typically 5V DC and resembles an AC sine wave but without uniformity or sequence.
Data is encoded as a digital signal(1s and 0s). -Information is regulated and uniformly sent between components. -Processors at either end decode and use this data.
Electrical signals pass through integrated circuits (ICs) and are transmitted through data cables (or wireless).

Digital Data Transfer

Ideal digital waveform is a square wave.
In practice, waveforms are distorted AC sine waves.
Voltage in digital systems represents binary data (0 V = 0, 5 V = 1).
System voltages can vary between 0V and 0.8V or between 2V and 5V (representing binary 0 and 1 respectively).

Practical Data Signal

Clock pulses represent the operating speed of a data bus.
Transmitter and receiver synchronize to these.
Data values like voltage for 1s are tolerances.
Any deviation creates errors in analogue signals contrasted with digital signals.

Serial Data Transfer

Data moves between parts of digital computers in two ways: parallel and serial.
Serial transfer involves sending data sequentially.
Data is triggered by clock pulses, synchronizing the transmitter and receiver.
Data is stored sequentially in memory before transfer to processing circuitry.
Serial is commonly used over long distances.

Parallel Data Transfer

Each bit transferred via a separate circuit.
Typically faster than serial.
Requires more hardware and more space (negligible, in comparison).

Multiplexing

Combining multiple information channels onto a single transmission medium.
Digital time division technique reduces the need for wires, increasing reliability.
Multiple channels are multiplexed onto a common line and restored at the receiver.
Rotary switches synchronized allow this, transmitting data sequentially.

Aircraft Multiplex System

Older avionics systems used numerous independent boxes connected via point-to-point wiring.
As systems increased, cockpits became congested, increasing wiring complexity and aircraft weight.
Current systems use a shared data bus to share information between numerous systems.

Avionics Data Bus Layout in an Aircraft

A Bus Controller (BC) manages communications over the multiplexed bus via data.
The BC, operated by the FMC, shares management over all components connected to the bus.
Interconnections are simplified; parallel digital devices use serial transfer.

Data Bus Systems

Data bus is an internal interface in aircraft for exchanging data.
Twisted-pair wires, shielded for EMF (electromagnetic interference) cancellation.
Data travel unidirectionally (simplex) or bidirectionally (duplex).
Communication is controlled, and one word transmitted at a time to prevent confusion (no free-for-all).

Data Bus Connectors

Multiplexer bus functions as an arterial highway - central computers connected to it.
Peripheral components attach via breakouts/couplers.
Similar to network or phone extensions.
Requires a Bus Controller for active use and management.

Bus Controller and Backup Bus Controller

Managing peripheral data transfer and control on the bus.
Peripheral data sent via commands.
Respond to commands from the bus controller (BC).
Backups systems to provide assurance of continued operation during faults.

Mil-Std-1553 Data Bus

Protocol standard and electrical characteristics.
Time-division multiplexing (TDM).
A uniform digital data communication medium.
Allows data sharing among various avionics systems.

Mil-Std-1553 Data Words

Three types: Command Words, Data Words, and Status Words..
Each word is 20 bits long with a 3-bit sync field.
Parity bit (ensuring odd number of 1s).
Sub-address for data storage/retrieval.
Word count specifies data quantity.

Mil-Std-1553 Data Transfer

BC commands RTs (remote terminals) to transmit/receive data.
Status words confirm successful data reception.
Handshaking between the two confirms successful interaction.

Mil-Std-1773

Fibre-optic cabling standard for MIL-STD-1553.
Eliminates electro-magnetic interference from signals.
Defines electrical and protocol characteristics.

ARINC 429

Unidirectional data bus specification.
Used extensively in communication in commercial aircraft.
Data transmission in 32-bit words.
Non-reliance on voltage levels for signal conveyance (simplicity).
One transmitter maximum.

ARINC 629

Time-division multiplex (TDM) system.
Allows for high-speed data transfer.
High data capacity, supports multiple users simultaneously.
Bidirectional.

ARINC Data Types and Labels

The label of a 20-bit word specifies what data is being sent and how to interpret it (and the rest of the word).
Various data formats to fit multiple transmission types.
Digital codes for interpretation.

ARINC Timing

Periodic mode for regular frequency data transfer (consistent).
Aperiodic mode for irregular frequency event data (asynchronous).

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Description

This quiz covers the operation of data buses within aircraft systems, detailing communication protocols like MIL-STD 1553 and ARINC 429. It also explains the fundamentals of electric power transmission and its applications in aviation, including how electricity is generated and distributed to aircraft systems.