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ELEC 1620-Digital Electronics > Digital Electronics > Flashcards

Digital Electronics Flashcards

1
Q

What are transistors?

A

In simple terms they can be considered to be switches.

They can open and close to let or stop current flowing through it.

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2
Q

Moore’s Law

A

Every two years the transistor count in an integrated circuit will double

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3
Q

MOSFET’s

A

Metal-oxide semiconductor field-effect transistor
Made from silicon
Made using complementary metal-oxide semiconductor (CMOS)
By applying voltage to the gate, you can control the current flow between drain and source

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4
Q

Types of transistors

A

n-type (n-FET)
n-types don’t let current through by default
p-type (p-FET)
p-types do let current through by default

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5
Q

What’s an embedded system?

A

A device containing a computer that interacts with its environment using sensors, displays or actuators.
Usually only designed for a few or only one task

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6
Q

What’s a microcontroller?

A

Can be thought of as a computer system in a single-chip

They are programmed with software that tells it how to interact with hardware and peripherals

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7
Q

Definitions of sampling

A

Sampling: how many times per second an anologue signal is read
Measured in Hz

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8
Q

Definition of quantisation

A

A method of discretising an analogue signal
This means the amplitude can only take on of several discrete values/levels
Number of values it can take is called bit depth
For n bits there 2^n levels

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9
Q

AND, OR, NOT symbol and function

A

AND: D shape, only if both inputs are 1
OR: D with with curved back shape, if one or both inputs are 1
NOT: Triangle with a cirlce on pointy end. Inverts input

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10
Q

Logic gate algebra: AND, OR, NOT, NAND, NOR

A

AND: y=a.b
OR: y=a+b
NOT: y=a(line above a)
NAND, NOR: line above AND/OR algebra

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11
Q

Buffer, XOR, XNOR

A

Buffer: y=a, input=output, used to amplify current in circuit
XOR: y=a⊕b, one or the other but not both
XNOR: XOR equation with a line above it, none or both

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12
Q

Logic levels

A

Get henry to explain these

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13
Q

Creating XOR and XNOR logic circuits

A

Write the truth table, use SOP algebra to figure it out

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14
Q

Multiplexer + De-Multiplexer

A

M: Connects multiple inputs to a single output. Use truth table to figure out logic circuit
DM: Connects multiple outputs to a single input

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15
Q

Programmable Array Logic (PAL)

A

Has a programmable AND array and fixed OR array.

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16
Q

Creating basic gates with NAND and NOT gates

A

Revise this

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17
Q

Creating NOT and NAND gates from transistors

A

Revise this

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18
Q

Max number that can be stored in a given number of binary and hexdecimal digits

A

n=number of digits
Binary: 2^n - 1
Hexadecimal: 16^n - 1

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19
Q

Converting decimal to hex, vice versa

A

Convert to binary first. Then split into two sets of 4 digits

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20
Q

Sum of products and boolean algebra

A

Revise this

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21
Q

Writing binary numbers using sign-magnitude

How does this affect the range? What’s special about zero?

A

Most significant but represents sign
0 = positive number
1 = negative number
Remaining bits represent magnitude of number
Range is smaller as one bit is used for sign (-2^(n-1) + 1 to 2^(n-1) - 1)
Two ways to represent zero (1000 and 0000)

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22
Q

1’s Complement definition and range

A

1’s: Positive numbers are represented like in sign-magnitude. Negative numbers have MSB of 1 but the magnitude bits are inversed (opposite to positive bits)
Range is same as sign-magnitude

23
Q

2’s Complement definition and range

A

Positive numbers are represented same as sign-magnitude.
Negative numbers have MSB of 1. Magnitude bits are the inverse of positive magnitude bits PLUS ONE
Range given by -2^(n-1) to 2^(n-1) - 1

24
Q

Adding bits: how to do it, how to create a half adder circuit, when to use half adder?

A

Use column adding method. 1+1 results in a carry
Half-adder: create a truth table with two inputs, a sum and a carry column. Use boolean algebra
Use only for single-bit addition

25
Q

Full-adder circuit creation

When to use a full-adder circuit?

A

Create a table with 5 columns: two inputs, a carry-in, a sum and a carryout. Remember: a 1 in one column is a sum, two is a carryout and three is sum and carryout.
Use when adding multi-bit numbers

26
Q

How does a ripple-carry adder work?

A

Multiple full-adders (one for each bit) connected in parallel
Carry-out of each FA is passed into the carry-in of the next FA
First FA in chain is least-significant-bit with carry-in set to 0
Final FA is most-significant-bit

27
Q

Arithmetic Logic Unit: definition, how many input and output bits and how many operations can be performed

A

A combinational logic circuit that performs arihmetic and logical operations on binary numbers
Two inputs, one output and ‘n’ number of control bits
For n control bits, a maximum of 2^n operations can be selected from

28
Q

How does a binary adder do subtraction?

A

Y=A-B

Y=A+(-B)

29
Q

The four different flags that can occur from a ALU

A

C-carry: the final carry-out of the ripple carry adder. Not applicable to signed numbers
V-overflow: signed numbers can only take value in a certain range. Overflow is when result goes out of this range. Occurs when the sign bit changes Not applicable to unsigned numbers
N-negative: whether the MSB is negative. Not applicable to unsigned numbers
Z-zero: Whether the output is zero

30
Q

Sequential logic circuits-how do they differ from combinational circuits?

A

Current output depends on both the current and previous inputs-output is funneled backed into the circuit. Forms basis of memory

31
Q

What’s a synchronous circuit?

Whats a asynchronous circuit?

A

Sequential logic circuit where a clock signal is applied to the circuit. Clock signal is a periodic waveform of frequency f
Circuit only updates output on a clock-edge
Circuit can be positive or negative-edge triggered
Asynchronous: sequential circuit without a clock signal

32
Q

Flip-flop definition, most common type and how it works

A 
A bi-stable multivibrator circuit
Bi-stable means it has two stable states
Can store a single bit indefinitely
D-type flip-flop
Two inputs, D and E. D is data input, E is enable input which determines whether output will change or not. 0 locks it, 1 unlocks it
Two outputs, Q and NotQ
33
Q

What’s a register? What’s it used for?

A

Multiple flip-flops grouped together to store nultiple bits. Very high-speed memory but very expensive

Used to store very small amounts of data inside a CPU

34
Q

Two ways to read and write data to registers

A

Serial-in/Serial-out: bits are loaded in one at a time. Outputs from one flip-flop are passed into the input of the next.
Takes n clock cycles for a n-bit register
Parallel-in/Parallel-out: each bit from the data bus is fed into an individual flip-flop
Data will be written to the register in a single clock cycle

35
Q

Shift register definition
What weird thing can shifting do?
Shift/Load in registers

A

Devices that do parallel-to-serial conversion
Shifting to the left multiplys binary number by 2 (division to the right)
Operation determined by multiplexers.
Shift shifts a values in registers serially
Load loads a new value

36
Q

Microcontroller definition and uses

A

A computer on a single chip
Contains a CPU, memory and various peripherals
Used in embedded systems to work with sensors

37
Q

Different ways to use the term architecture

A

Instruction set architecture (ISA): describes the instructions
Microarchitecture: refers to how the ISA is implemented in hardware
System architecture: describes the computer system
Load-store architecture: type of processor design

38
Q

Definition of a computer

A

A fixed hardware platform that can carry out an almost infinite number of tasks

39
Q

Program counter, incrementer

A 
Program counter (PC): contains address of next instruction to be executed
Incrementer: increments value of stored in PC
40
Q

MAR, MBR

A

Memory access register (MAR): stores address of memory location currently being accessed
Memory buffer register (MBR): stores data that has just been read from memory/data to be written to memory

41
Q

IR, control unit

A 
Instruction register (IR): stores instruction currently being executed
Control unit: subsystem that controls the CPU
42
Q

Definition of byte-organised memory

How many memory locations can a n-bit address hold?

A

Each location in memory can store an individual byte with a unique address
n-bit address allows 2^n memory locations

43
Q

How many bytes are in a kb, Mb, Gb?

A

1 kb: 2^10
1 Mb: 2^20
1 GB: 2^30

44
Q

Describe the fetch part of the fetch-execute cycle

A 
Value in the PC is copied to the MAR
Location of value in MAR is found and read from memory
Instruction is copied to MBR
Contents of MBR is copied to IR
Value of PC is incremented
45
Q

Decoding data: how types of instructions are there and what figures out how to use the instruction?

A

Data procressing (done by ALU)
Loading data from memory
Storing data in memory

Control unit determines what kind of instruction is in the IR and how to proceed

46
Q

What’s pipelining?

A

Increases performance
While the first instruction is being decoded, the second instruction is fetched. While the first instruction is being executed, the third can be fetched etc.

47
Q

RISC and CISC: definition and pros/cons

A

Reduced/complex instruction set computer
RISC has simpler architecture with fewer instructions
CISC has complex architecture with lots of complex instructions
CISC is simpler to write programs for but RISC instructions can be executed quicker

48
Q

Harvard vs Von Neumann architecture

A

Von Neumann: instructions and data both share the same bus
Creates bottleneck tho
Harvard: data and instructions are stored in seperate memories and have different buses

49
Q

Counters: definition and max count value

A

Sequential logic ciruict element
Built using flip-flops
Max count value is 2^n - 1 where n is the number of flip-flops

50
Q

JK flip-flop definition

A

Flip-flop that can be made to toggle the value it is currently storing

51
Q

Synchronous and asynchronous counters

A

Synchronous: all flip-flops share a common clock signal
Asynchronous: not all flip-flops are clocked. First one is clocked and the others are clocked by an output from the previous flip-flop
Known as ripple counters

52
Q

Asynchronous counters

A

Frequency dividers: each subsequent flip-flop toggles at the half the frequency compared to the last one
Counters can therefore be used to scale down the original clock frequency
Used in quartz clocks

53
Q

Resolution vs range in a counter, and how pre-scalers help

A

Resolution is how often a clock ‘ticks’, range is how long a clock can count for. Higher resolution means lower range
Pre-scalers allow users to modify clock frequency and find the best balence

54
Q

Encoders and watchdog timers

A

Encoders count clock cycles between events
WT: a counter that constantly increments and has to be reset before overflow happens. If software crashs and it isn’t reset, whole system reboots

ELEC 1620-Digital Electronics (2 decks)

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