Digital Fundamentals

Question 1

Name the two categories of electronic circuits and describe them

Answer 1

• Digital and Analogue
• An analogue circuit processes continuos signals
• A digital circuit is designed for the processing of discrete signals
• Analogue signals are varying continuously
• Digital signals have a discrete set of values

Question 2

Name 4 advantages of Digital circuits

Answer 2

• Digital data can be processed and transmitted more efficiently
• More reliable
• More compact for storage
• Can be reproduced with greater accuracy and clarity

Question 3

Uses of digital circuits in aircraft

Answer 3

• modern computer systems
• flight deck controls linked to control surfaces on more modern aircraft

Question 4

How do digital waveforms work?

Answer 4

Consist of voltage levels that changes back and forth between the high and low level or states

Question 5

What is a Positive-going pulse?

Answer 5

Starts from a baseline or a lower voltage level, going to the high voltage level

A waveform consists of a rising/leading edge and a falling/trailing edge

Question 6

What is a Negative-going pulse?

Answer 6

A pulse/waveform that starts from a baseline or a higher voltage level, going to the lower voltage level

A waveform consists of a rising/leading edge and a falling/trailing edge

Question 7

What is the difference between a periodic and a non-periodic pulse trains/waveform?

Answer 7

In a period pulse waveform the series of pulses repeat at regular intervals and the period pulse remains constant

In a period pulse waveform the duration of the signal is at a high level

Question 8

What is the Duty Cycle?

Equation

Answer 8

Duty Cycle = (t_w/T)100%

Where t_w is the duration the signal is at a high level

Question 9

How many possible states are there for digital electronics?

Answer 9

Two. (A high voltage and a low voltage)

Question 10

What is binary?

Answer 10

A two-state number system with two digits 0 and 1

Question 11

What is a binary digital called?

Answer 11

A bit

Question 12

How does binary information appear?

Answer 12

As waveforms of a sequence of bits

Question 13

What is necessary to synchronise all the binary waveforms?

Answer 13

A clock

Each change of waveform occurs at the leading edge of the clock.

Question 14

What is data?

Answer 14

Data refers to groups of bits that convey some type of information.

Question 15

Name two ways in which binary data can be transferred.

Answer 15

In serial or parallel.

Question 16

How are serial and parallel transfer different?

Answer 16

In serial the bits are sent along one after the otherr in a single communication channel, whereas in parallel multiple bits are sent simultaneously using seperate communication lines.

Question 17

What is an LRU?

Answer 17

A self-contained unit that performs a specific function within an avionic system.

Line Replaceable Unit

Question 18

Give uses of a LRU?

Answer 18

Flight Control Computerr, Communication Transiever, Navigation System, and Radar processor

Question 19

What does BJT stand for?

Answer 19

Bipolar Junction Transistor

Question 20

What is a BJT?

Answer 20

A bipolar junction transistor is manufactured with three semiconductor regions that are doped differently. (pnp or npn)

Question 21

What are the parts of a BJT?

Answer 21

Collector, Base and the Emitter

Question 22

What are the conditions for the BJT to operate?

Answer 22

The base-emitter junction must be forward biased whilst the base-collector junction must be reversed-biased.
- the emitter region is heavily doped
- npn transistor - the n-type emitter region has a very high density of free electrons
- pnp transistor the p-type emitter region has a very high density of holes.

Question 23

What is ARINC 429?

Answer 23

Aeronautical Radio Incorporated.
A two wire, point to point data bus that is application-specific for commercial and transport aircraft.
Most common;y used avionics data bus communication protocol in commericial aircraft.
Unidirectional data bus standard

Question 24

How is data transmitted in ARINC?

Answer 24

• In packets of 32 bits
• Transmitted at a bit rate of either 12.5 kbs or 100 kbs

Question 25

What is ARINC 429 used for?

Answer 25

- To implement serial line communication - to connect LRUs up to 90 metres apart - point-to-point communication - one source (transmitter) is able to connect to 20 LRUs max

Question 26

What are the 5 primary fields of ARINC 429?

Answer 26

- Label : 8 bits - Source/Destination Identifiers (SDI) : 2 bits - Data : 19 bits - Sign/Status Matrix (SSM) : 2 bits - Parity : 1 bit

Question 27

What does the label section of ARINC 429 do?

Answer 27

Identifies the type of information contained in the word. An example is ground speed.

Question 28

What do Source/Destination Identifiers in ARINC 429 do?

Answer 28

Used in addition to the label to identify where the data came from or where it is supposed to go.

Question 29

What does Data do in ARINC 429?

Answer 29

Contains the meaningful information in the word. ARINC 429 data types include BNR (binary), BCD (binary coded decimal)

Question 30

What does the sign/status matrix do in ARINC 429?

Answer 30

Conveys supplementary information associated with data, encompassing attributes like polarity, cardinal direction, failure warnings, functional tests, absnce of computed data, and normal operation.

Question 31

What does parity do in ARINC 429?

Answer 31

Used to detect bit-encoding errors.

Question 32

What is logic?

Answer 32

Logic is the realm of human reasoning- a certain proposition is true if certain conditions are true.

Question 33

What are logic functions?

Answer 33

true/false or yes/no statements, digital circuit with their two-state characteristics - three basic logic functions: NOT, AND, OR

Question 34

What is a circuit called that performs a specific logic function?

Answer 34

A logic gate

Question 35

Describe the sysmbols for a NOT, AND and OR gates.

Answer 35

NOT: triangle with circle at point AND: square with semicircle side OR: fat curvy triiangle

Question 36

What does a NOT gate do?

Answer 36

- changes one logic level to the opposite - so 0-->1 or 1-->0 - also known as an inverter - with 0 input, the transistor switch is held open by the negative base voltage and the output is +5V (1) - A positive input voltage (1) forward biases the emitter junction, the transistor working in the saturation region, the output is low voltage (0)

Question 37

What does an AND gate do?

Answer 37

- produces a high output only when all the input are high - 0 + 0 = 0 - 0 + 1 = 0 - 1 + 0 = 0 - 1 + 1 = 1 - output = input A * input B

Question 38

What does the OR gate do?

Answer 38

- produces a high output when one or more inputs are high - 0 + 0 = 0 - 0 + 1 = 1 - 1 + 0 = 1 - 1 + 1 = 1

Question 39

What is a NAND gate?

Answer 39

- does the opposite of an AND gate - 0 + 0 = 1 - 0 + 1 = 1 - 1 + 0 = 1 - 1 + 1 = 0

Question 40

What does a NOR gate do?

Answer 40

- opposite of an OR gate -0 + 0 = 1 - 0 + 1 = 0 - 1 + 0 = 0 - 1 + 1 = 0