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electrical engineering > Digital COPY > Flashcards

Digital COPY Flashcards

1
Q

What are the advantages of digital electronics over analogue ?

A

Low mass production costs Implementation of complex algorithms No drift or ageing problems (As it heats up and cools down over time) Good immunity to noise and signal degradation

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2
Q

What happens to noise when a digital and analogue signal is processed?

A

In digital the noise to totally removed. Analogue the noise gets worse

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3
Q

What is combinational logic?

A

Provides and output the is dependent on the input at that point in time. Like a light switch

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4
Q

Sequential logic

A

An output is determined not only by current input but also previous history. Like a pull cord switch in a bathroom.

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5
Q

Synchronous logic

A

A clock switches between 1 and 0 to ensure all the sub-systems are synchronised.

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6
Q

What is the most significant bit?

A

The left most bit

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7
Q

If you have n bits, how many numbers can you store?

A

2^n numbers. Remember to include 0

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8
Q

What is a byte?

A

A group of 8 bits

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9
Q

What is a word?

A

2 bytes

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10
Q

Convert 7B to denary

A

7*16^1 + 11*16^0 =123

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11
Q

C to denary

A

12

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12
Q

D to denary

A

13

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13
Q

E to denary

A

14

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14
Q

F to denary

A

15

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15
Q

How do you convert denary to hexadecimal ?

A

Divide by 16. The remainder is the least significant digit. Continue until you have one remainder left which is the most significant digit. If the remainder was 13 it would be D.

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16
Q

Why isn’t binary used in measurement of real things?

A

A slight miss-alignment of the sensor would cause a miss reading.

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17
Q

What is the nature of grey code?

A

Going from number to number only one digit changes

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18
Q

How do you convert from 3 bit binary to grey code?

A

The most significant bit of the grey code is the same as for the binary For all other bits if it is the same as the one before it is 0. If different it is 1

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19
Q

What is an ADC?

A

Analogue to digital converter. Takes a continuously varying input and converts to binary numbers.

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20
Q

What is quantisation error?

A

The difference between the digital and analogue signal.

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21
Q

How can the quantisation error be reduced?

A

Increase the number of bits.

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22
Q

How do you find the quantisation error?

A

voltage step = (Vmax-Vmin)/2 The error is half of this again.

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23
Q

How does an and gate work?

A

If both inputs are 1, output is 1 Otherwise output is 0. Referred to as the logical product.

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24
Q

What is the symbol of an and gate?

A

A square with the side where the output comes from is rounded off.

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25
Q

How does an or gate work?

A

If both the inputs are 0, the output is 0 Otherwise the output is 1. Sometimes referred to as the logical sum of A and B

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26
Q

What is the symbol for the or gate?

A

A shield on its side with the output coming from the pointy end.

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27
Q

What are the different types of or?

A

Inclusive or which is used by the or gate Exclusive or which only returns 1 when the two inputs are different. C=A⊕B

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28
Q

What is the symbol for an inverter?

A

A triangle pointing to the right with a circle at the point B=À

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29
Q

What should A+B.C be interpreted as?

A

A+(B.C) And has precedence over or.

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30
Q

How would you estimate the complexity of an equation?

A

Add together the total number of inversions. (little hats) The number of plus signs and the total number of letters.

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31
Q

What is de morgan’s law?

A

(A.B)=(A)+(B)

(A+B)=(A).(B) where () denote an invertion

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32
Q

What is a Nand gate?

A

And and gate with an inverter at the end c=(A.B)

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33
Q

What is the truth table for the RS latch?

A
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34
Q

What is the truth table to the active low RS latch?

A
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35
Q

What is the truth table for the JK flip-flop

A
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36
Q

What is the truth table for the T flip flop?

A
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37
Q

what is the truth table for the D flip flop?

A
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38
Q

How do you design a counter?

A

Draw these tables. Then drae K maps with Q values now on the axis for each of the T columns.

Then attach several T flip flops together, all connected directley to the clock and wire up accordingly.

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39
Q

What is a modulo counter?

A

Used when the number of inputs is not equal to 2^n.

For examle a modulo 6 counter would go through the sequency 0,1,2,3,4,5,0,1,2,3…

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40
Q

What is the standard symbol for the 2 bit multiplexar?

A
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41
Q

How do you tell if adder overflow has occoured in unsigned binary?

A

Look at the final carry output. If this is a 1 it has over flowed. This is a status flag.

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42
Q

What is a carry ripple adder?

A

A series of full adder put together. However, each adder adds a bit of a time delay.

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43
Q

How can the build of delays in an adder be mitigated?

A

All of the carry on values can be expressed in terms of all the previous A and B values. This means they can be calculated from the starts without waiting for anything else.

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44
Q

How does the XNOR gate work?

A
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45
Q

How would you make a equality detector?

A

The XNOR gate outputs a 1 when the two inputs are the same. Put all the pairs of bits through a different XNOR gate and and the results together. When equal it should give a 1.

46
Q

What is the 2s complement number system?

A

The most significant bit is negative

47
Q

How do you convert a number to the negative/ find the complement?

A

Write is positive.

Invert each 1 to 0 and 0 to 1

Add 1

48
Q

How would you add bits to a negative 2s compliment number?

A

If it was positive you would just add 0s to the front.

When negative add 1s to the front

49
Q

What modifications need to be done to an adder so it can add signed binary?

A

None, it will work fine.

50
Q

How are numbers subtracted?

A

Convert one of the numbers to a negative and add together. This can be done with an ordinary adder by putting inverters on all the B or A inputs and making Cin=1

51
Q

How can a circuit that adds and subtracts be produced?

A
52
Q

What is an ALU?

A

Arithmetic logic unit. You specify numbers which you want to add and the operation you want to get a given output.

53
Q

How can you tell if there is overflow in signed binary?

A

When the most significant bit’s Cin and Cout are different.

(That is the remainder that it produces and the remainder it got from the bit to the right)

54
Q

What are the four basic parts of programmable sum-of-products function?

A

An input stage, an AND plane, giving products, an OR plane evaluating sums and an output stage that might include filp flops.

55
Q

What does PLD stand for?

A

Programmiable logic device

56
Q

What a way of notation that is useful when drawing large PLDs?

A

An X deonotes a connection. Thus C isn’t connected to the OR gate.

57
Q

What does PROM mean?

A

Programmable read only memory. Where the AND array is fixed and the OR array is programable

58
Q

What does PAL mean?

A

Programmable array logic where the AND array is programmable but the OR array is fixed.

(Also known as generic array logic and programmable electrically erasable logic)

59
Q

What is a PLA?

A

Programmable logic array. Where both the AND and OR array are programmable.

60
Q

What is RAM?

A

Random Access Memory. New data items can be stored into the memory, old data iteams can be read out

61
Q

What is ROM?

A

The data contained is fixed at the time of programming and can’t be changed untill reprogramming. We can read data but can’t write more.

62
Q

What is volatile memory?

A

When the power is turned off the memory is lost. RAM is this as it is voltage in a latch circuit.

ROM is an absence of a connection between the AND and OR plane which will remain.

63
Q

What is a tri-state output?

A

A device that can electronically disconnect itself from its output terminal.

For an active high tri-state buffer, when OE=0 it will go to a high impedance state and act as if it weren’t connected.

For an active low tri-state buffer, when when OE=0, nothing will happen and the signal can just pass through.

64
Q

What is the advantage of using a tri-state output?

A

It allows for several devices to put their outputs through the same wire without interfering.

65
Q

If on a diagram, you see a wire with a slash across it with a number, what does that mean?

A

The wire is infact 8 wires carrying 1-bit signals that form a data byte.

66
Q

What is the symbol of an ALU?

A
67
Q

What is a register?

A

A circuit with shoer term memory. A calculator would have it so that when doing 3+5 you didn’t have to press all three buttons at the same time.

68
Q

How could a register be made from D flipflops?

A

The output of a D flipflop will only change on a clock edge, meaning it has some memory. If 8 are connected to the same clock signal, they can store a byte.

69
Q

What are the main features of a microprocessor?

A

Normally designed to be one chip within a larger computer system with other chips that might do RAM. Normally used in what is pecerved to be a computer. The program can be changed frequently.

70
Q

What are the main features of a microcontroller?

A

Work in an embedded system. They will only run a single program which is stored in ROM. They aim to put all the required resorces on a single chip and have very low power and resource requirments.

71
Q

What is A+1 equal to?

A

1

72
Q

What is a bistable?

A

A bistable is a circuit whose output can remain in one of the two stable states infinitely, even if the input changes to zeros

Same as a flip flop

73
Q

What is a diagram for the RS flip flop?

A

X and Y are Q and Q’

74
Q

What counting system does % denote?

A

Binary

75
Q

What counting system does $ denote?

A

hexadecimal

0x also means hexadecimal

76
Q

How might you convert hexadecimal to binary?

A

Replace each hexadecimal digit by four binary digits. Example: 0x2.4 = ?2

0x2.4 =0010.01002= 10.012

77
Q

What is a nibble?

A

A collectio of 4 bits.

78
Q

Embedded system/controller

A

Embedded system/controller: An embedded controller is a microprocessor or microcontroller with its auxiliary components and circuit designed to be used dedicatedly to a particular device.

79
Q

Program counter (PC):

A

Program counter (PC): A PC is a register which contains the address of the next instruction in the memory to be executed.

80
Q

Memory address register (MAR):

A

Memory address register (MAR): It contains the address of the current instruction being executed

81
Q

Memory buffer register (MBR) or memory data register (MDR)

A

Memory buffer register (MBR) or memory data register (MDR): It stores the data or instruction fetched from MAR in a reading cycle, and the data to be transferred to MAR in a writing cycle.

82
Q

Instruction register (IR)

A

Instruction register (IR): it stores the fetched instruction.

83
Q

Data registers or accumulator

A

Data registers or accumulator: A data register D0 or a accumulator holds temporary or intermediate results during a calculation. Most 8-bit and some 16-bit processors have only one general purpose data register. New 16-bit processors have more data registers

84
Q

What are the different flags which pertain to arthimetic operations.

A
85
Q

What is a bus? and what are the different types?

A

A bus is a bundle of wires for reading and writing between CPU and other components 

  • Data bus is for carrying data
  • Address bus makes the data bus linking CPU with a memory address exclusively
  • Control bus is for executing read/write actions.
86
Q

A Pentium 4A (Northwood) has 64-Bit Data Bus, 32-Bit Internal Register, 36-Bit Address Bus. How much is its maximum memory size ?

A

A Pentium 4A (Northwood) has 64-Bit Data Bus, 32-Bit Internal Register, 36-Bit Address Bus. How much is its maximum memory size ?

Answer: 236 =64G

87
Q

What is EEPROM

A

EEPROM: electrically erasable programmable read only memory.

88
Q

Static RAM (SRAM):

A

Static RAM (SRAM): an RS flip-flop constructed by six transistors is used for storing one bit data. The data will stay there untill it is rewritten.

89
Q

– Dynamic RAM (DRAM):

A

a capacitor is used capable of storing charge delivered to it through the access transistor. Refreshing the memory contents is needed for DRAM in typically every 16 ms.

90
Q

SRAM v DRAM:

A

SRAM v DRAM:

 SRAM are fast (25ns) and expensive, suitable for cache

 DRAM are compact and low cost, at a reasonable speed (150, 120, 100, 80, 70 and even 60ns )

91
Q

What is the difference between machine code and assembly language?

A

The primitive instructions that directly control the operation of a computer are called machine code instructions and are composed of sequences of binary values stored in memory. An assembly language is shorthand permitting the programmer to write machine instructions in a simple abbreviated form of plain language.

92
Q

What’s the difference between a memory location and a data register?

A

A memory location is a part of the whole memory area provided by the computer. It is for storing a program instruction, or data. A register in a computer is a storage, and is designed to be accessed by the processor at an even faster speed than memory. Each register is for keeping one type of information, and its function is normally indicated by its name, such as IR, MAR, and Data Register D0.

93
Q

How do you know when overflow has occured?

A

When the MSB of the answer is different to that of both the things being added.

Not during subtraction

94
Q

Why are I/O devices needed?

A

 Interface devices and peripherals are included in a memory map.

 CPU’s signals are too fast for peripherals directly linked to the CPU.

 Interface devices are needed.

95
Q

Interrupt Driven I/O Basic Operation

A

Control & Timing

  • CPU (Processor) Communication
  • Device Communication
  • Data Buffering
  • Error Detection (e.g., extra parity bit)
96
Q

What are the two different ways to encode didgital infomation?

A
97
Q

Question: in a 7 bit serial interface, determine whether the data transfer has produced an error in the following cases: –

Parity even, 0110 1101 –

Parity odd, 1011 1100

A

Parity even, 0110 1101 – Error (the sum of “1” is 5, odd)

Parity odd, 1011 1100 Correct (the sum of “1” is 5, odd)

98
Q

How does the typical DAC work?

A
99
Q

Potentiometers

A

The potential difference across the load Vo is directly proportional to Vs .

Applications: to measure both linear and rotational displacements.

100
Q

Strain gauge

A

Placing : along the expected deformation direction. Applications: to measure deformations and deflections in microns.

101
Q

How does a capacitive touch screen work?

A

A layer of grid on top of the glass panel stores electrical charge. • When a finger touches the monitor, some charge is transferred to the user and the charge at the location decreases. • This decrease is measured in circuits located at each corner of the monitor and the touch location is calculated.

102
Q

Magnetic field sensors

A

Hall effect: The Hall effect is the voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879. • Hall voltage is proportional to magnetic field.

103
Q

Eddy current sensors

A

Eddy current: When a magnetic field intersects a conductor or vice versa, it causes a circulating flow of eddy currents with in the conductor. These eddy currents create electromagnets with magnet fields that oppose the effect of applied magnetic field, causing changes in impedance, which is used to find the distance between the sensor and target material. • Eddy sensors are used for detecting displacement without contact.

104
Q

CO2 gas sensors

A

Monitors how much infrared radiation is absorbed by CO2 molecules

 Measures CO2 levels in the range of 0-5000 ppm (parts per million)

105
Q

Ultrasonic sensors

A

Ultrasonic sensors are used for position measurements  Sound waves emitted are in the range of 2-13 MHz  Sound Navigation And Ranging (SONAR)

106
Q

What is the difference between a passive and an active infrared sensor?

A

The passive just takes in the IR emitted by things

The active emites IR waves and takes them in when they have reflected off. It can tell the difference between black and white.

107
Q

What is a latching circuit?

A
108
Q

Sensors and transducers

A

-

Sensors: devices which measure and respond to aparticular change.

Transducers: devices which convert energy from oneformat into another.

In many cases, sensors can be called transducers

109
Q

What is the control unit (CU)?

A

It takes the opcode (operation code in hexadecimal), from the instruction registed and generates signals to implement the action.

110
Q

What do the different busses do?

A

The address bus connects the CPU with a specific memory address;

The data bus will carry data

The control bus will execute read or write (R/W)

electrical engineering (3 decks)

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