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Digital Systems > Chapters 1 and 2 > Flashcards

Chapters 1 and 2 Flashcards

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1
Q

What is electrical current?

A

Is the movement of electrically charged particles caused by the electric field.

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2
Q

What is static electricity?

A

Is an immotile buildup of electrically charged particles on some object.

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3
Q

What is a diode?

A

A diode is an electrical component with two terminals called anode and cathode

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4
Q

Define current, voltage and power.

A

Current is the rate of flow of electrical charge through a point int the circuit.
Voltage is the electrical pressure between two points in the circuit.
Power is the energy carried by the current.

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5
Q

What is a diode?

A

An electronic component that only lets electric current flow in one direction from anode(longer end) to cathode (shorter end)

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6
Q

Why do dioides require resistors?

A

A dioide requires a certain amount of voltage to be applied to start conducting. After this voltage is achieved its resistance is very low and current will burn out quickly.

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7
Q

Which binary value represents a high voltage? Are these values exact in the most accurate of todays computers?

A

High = 1
Low = 0

No because of electrical interference, they are approximations

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8
Q

What does ASCII stand for?

A

American Standard Code for Information Interchange.

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9
Q

What do CR and LF do?

A

Carriage Return (CR) tells the printer to return the carriage to the start of the page (left-side).
Line Feed (LF) tells the printer to move the paper up one line.

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10
Q

Power formula for electric circuit.

A

P = VI

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11
Q

How do digital signals attempt to stop bit errors?

A

A 1 is recorded for a range of voltage
A 0 is recorded for a range of voltage
A range between them is left as unacceptable.

This buffer ensures if there is an error we will know about it.

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12
Q

Explain LCD (student number thing) operation.

A

RS = 0 (encodes an instruction)
RS = 1 (encodes a character)
E toggled from 1 to 0 to perform action
DB7-DB0 makes up instruction/character

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13
Q

T or F. At low temperatures silicon is a conductor.

A

False, all electrons are tied up in covalent bonds act as an insulator.

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14
Q

What happens when silicon is heated?

A

Some electrons beak out from covalent bonds leaving behind positively charged empty spaces known as holes. The free electron moves about until it recombines with another hole. This will cause electric current to flow when voltage is placed across the crystal.

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15
Q

Why is Phosphorus added to silicon?

A

A phosphorus atom has 5 valence electrons so 4 bond with the silicon and the 5th is free to move. There is an excess of negative electrons. So this is an n-type semiconductor.

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16
Q

Why is boron added to a silicon atom?

A

A boron atom has 3 valence electrons so 3 bond with the silicon but a positive hole is left as one of the silicon atoms will be missing an electron. There is an excess of positively charged holes which cause electrons to move. So this is a p-type semiconductor.

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17
Q

Explain operation of nMos transistor?

A

Two n-type semiconductors have a p-type semiconductor placed between them.
Source goes into n-type, gate into space between n-types and drain out from other n-type.

When a negative charge is applied to the gate current doesn’t flow.

When a positive charge is applied to the gate current flows as the positive holes in the p-type are pushed back allowing the n-type conductors to channel electrons from source to drain.

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18
Q

How is pMos transistor denoted in digital circuits?

A

Same as nMos but with circle at the gate.

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19
Q

What input at gate does pMos and nMos need for current to flow?

A

pMos 0
nMos 1

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20
Q

T or F. Switching transistor ON or OFF has no time delay.

A

False.

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21
Q

T or F. The higher the clock frequency the higher the power consumption.

A

True.

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22
Q

What is an integrated circuit?

A

An electronic circuit formed on a small piece of semiconducting material, which performs the same function as a larger circuit made from discrete components.

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23
Q

What is the difference between a combinational circuit and a logic circuit?

A

Combinational: One or more logic inputs and ONE OR MORE logic outputs.

Logic: One or more logic inputs and ONE logic output.

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24
Q

T or F. Combination logic has no memory.

A

True.

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25
T or F. At all times, the output is only dependent entirely on the current input for combinational logic.
True.
26
What is sequential logic?
Sequential logic consists of logic gates which are connected together to produce a specified output for certain specified combinations of current and previous inputs.
27
How does sequential logic differ from combinational logic?
Sequential logic depends on previous inputs and not just current inputs. It has memory unlike combinational.
28
Precedence order acronym for Boolean algebra.
BNCDIE
29
What is a timing diagram informally?
A truth table in the horizontal with 1's showed as humps and 0's as dips. Can also have inputs in any sequence and shows how output changes with time.
30
What is logic synthesis?
Logic synthesis is the process by which an abstract description of desired circuit behavior is turned into a design implementation consisting of logic gates.
31
If a circuit has N inputs into Boolean AND or OR and N = 2^i? How many gates does the circuit have and how many levels?
Gates = N - 1 Levels = i N/2 : N/4 : N/8 : .... : 1
32
What is logic simplification?
The purpose of logic simplification is to reduce the area of the circuit while keeping the same functionality.
33
State XOR rules.
'AB + A'B = A ⊕ B 'A'B + AB = '(A ⊕ B)
34
Distinguish between variable, complement and literal.
Variables is X Complement is 'X Literal is X and can also be 'X
35
Define SOP.
Sum of Products expression consists of two or more product terms summed by Boolean addition.
36
What is the domain of a Boolean expression?
The set of variables contained in it.
37
Define SSOP.
A standard sum of products expression is one in which all of the variables in the domain appear once in each product term in the expression.
38
Explain Karnaugh Map implementation.
1. Draw empty Karnaugh Map 2. Determine binary value at each cell 3. Group 1's (Group size must be power of 2. Each 1 in group much be adjacent to a one horizontally or vertically. Table wraps around. Include largest number of 1's possible. Groups may overlap but not be subsets) 4. Convert groups to product terms 5. Add product terms
39
What form of boolean expression does a Karnaugh map output?
minimal SOP
40
What are the problems with Karnaugh Maps?
They do not find the minimal circuit. - Factorizing can reduce circuit size - Resultant SOP can be transformed into sub-expressions such as XOR to further reduce size.
41
Explain how Karnaugh maps work with don't care values.
Same except as don't care values can be treated as a one to help make groups bigger. But don't need to be included.
42
Define POS.
A product of sums expression is the result of multiplying two or more sum terms.
43
Define SPOS.
Standard Product of Sums is a Product of Sums with every sum term containing every variable in its domain.
44
How can SPOS expressions be obtained from truth table?
By constructing sum terms for all lines in the truth table that output 0 and adding them.
45
Why are NAND and NOR gates called universal?
Any truth table can be implemented using logic gates made entirely of NAND (or alternatively NOR) gates.
46
What is the transition time?
Is the time taken for a wire to switch between logic levels.
47
What is the propagation delay?
Is the time between the 50% point in an output logic level transition and the 50% point in the input logic level transition giving rise to the output change.
48
What is a glitch?
Is a voltage or current spike of short duration, which could lead to error.
49
What is a logic path?
Is the list of wires and gates between a circuit input and a circuit output.
50
What is the critical path?
Is the logic path associated with the longest delay between an input transition and a consequent output transition.
51
Give one reason critical path delay might be inaccurate.
Temperature.
52
Why are circuits not always optimized to reduce critical path delay?
As this change could lead to an increase in area.
53
What components in a computer cannot be represented by a combinational circuit?
Data registers, program counter, random access memory.
54
Explain 1-of-n decoders.
Has n inputs and 2^n output. Each output corresponds to one possible combination of input bits. Only one output active at a time.
55
What are buses?
A bus is a group of parallel wires through which data is transferred. Shown as one wire for ease on circuit diagram.
56
Explain multiplexers.
Retransmits one of their inputs as their output based on the value of select
57
Explain demultiplexers.
Retransmit their input as one of their outputs based on the value of select.
58
What is ALU?
Arithmetic Logic Unit can perform multiple arithmetic and logic operations. Inputs: X, Y, Operation Code. Outputs: Result
59
Why is NAND-type ROM better than NOR-type ROM?
NAND-type ROM packs more transistors in a unit of area than the NOR-type ROM.
60
Which type of ROM, encodes that the absence of a transistor encodes '1'?
NOR-type
61
Define combinational logic.
Combinational logic refers to a type of digital logic circuit in which the output is determined solely by the current inputs, without any memory or feedback loops. This means that the output is a direct function of the input signals at any given instant in time.
62
What do the following stand for? CMOS HDL
Complementary Metal-Oxide-Semiconductor Hardware Description Language
63
State Moore's Law.
The number of transistors on a microchip doubles approximately every two years, while the cost per transistor decreases.
64
In terms of digital circuits, what is a glitch? What causes it?
A glitch is a brief, unintended pulse or incorrect signal transition that occurs on a logic signal line. Glitches are typically caused by timing mismatches or transient conditions
65
State the truth table for a 2:1 multiplexer.
S (Select)A (Input 0)B (Input 1)Y (Output) 0 X X A 1 X X B
66
Define propagation delay.
Propagation delay in digital circuits refers to the time it takes for a signal to travel through a logic gate or circuit from its input(s) to its output.
67
What is contention in digital logic.
Contention refers to a situation where two or more components in a circuit attempt to drive a signal line (such as a wire or bus) to different logic levels simultaneously. This conflict can lead to errors, excessive power consumption, or even physical damage to the components involved.
68
What is a latch in digital logic?
A latch is a memory element that can store one bit of data. Its output depends on the input as long as enable is active. Once this control signal is inactive, the latch retains its state.
69
Explain circuit for frequency divider.
T flip flop with input connect to logic 1. T flip flop toggles. So output is clock of half the frequency.

Digital Systems (4 decks)

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