Logic Circuits

Question 1

what types of logic gates are there

Answer 1

AND, OR, NOT,NOR,NAND,XOR,XNOR

Question 2

What is an IC/”gate”

Answer 2

an electronic circuit that is constructed entirely on a single small chip of silicone

Question 3

What is a Dual In Line package (DIP)

Answer 3

a type of electronic chip with 2 rows of pins

Question 4

what is a fixed function logic

Answer 4

a category of digital integrated circuits having functions that cannot be altered

Question 5

what is programmable logic

Answer 5

a category of integrated circuits capable of being programmed to perform specific functions

Question 6

what is an ‘inverter’

Answer 6

performs the boolean NOT operation (X = ~ A)
- input is HIGH, output is LOW and vise versa

Question 7

what is the ‘AND’ gate

Answer 7

X = A.B or X = AB

produces a HIGH output when all inputs are high

Question 8

what is the ‘OR’ gate

Answer 8

X = A+B

produces HIGH output if any input is HIGH
- if all inputs are LOW, output is LOW

Question 9

what is the ‘NAND’ gate

Answer 9

X = A.B (bar on top) = AB (bar)

produces LOW output when all inputs are HIGH, otherwise all output is HIGH
- universal gate

Question 10

what is a ‘NOR’ gate

Answer 10

X = A + B (bar)

produces a LOW output if any input is HIGH
All HIGH = LOW
All LOW = HIGH

Question 11

what is a ‘XOR’ gate

Answer 11

X = A(bar)B + AB(bar)

output is HIGH if inputs are different

Question 12

what is a “XNOR” gate

Answer 12

X = AB bar + AB

produces a HIGH output if inputs are the same logic level

Question 13

what is a complement

Answer 13

the inverse of a variable & is indicated with an overbar

Question 14

what is a literal

Answer 14

a variable or its complement

Question 15

what IC is used for Boolean addition

Answer 15

OR operation

Question 16

what IC is used for Boolean multiplication

Answer 16

AND operation

Question 17

How does the variable order affect the addition commutative laws

Answer 17

no difference

Question 18

How does the variable order affect the multiplication commutative laws

Answer 18

no difference

Question 19

How does the variable order affect the addition associative laws

Answer 19

when OR-ing more than 2 variables, the result is the same regardless of how it has been grouped

Question 20

How does the variable order affect the multiplication associative laws

Answer 20

when AND-ing more than 2 variables, the result is the same regardless of how it has been grouped

Question 21

what is DeMorgans 1st theorem

Answer 21

the complement of a product of variables is equal to the sum of the complemented variables

AB bar = A bar + B bar

Question 22

what is DeMorgans 2nd theorem

Answer 22

the complement of a sum of variables id equal to the product of the complemented variables

A + B (BAR) = A bar . B bar

Question 23

what occurs if a variable has 2 overbars

Answer 23

cancel out

A double bar = A

Question 24

what is a karnaugh map

Answer 24

a tool for simplifying combinational logic

• simplify combinational logic by grouping cells and eliminating variables that change

Question 25

what is combinational logic

Answer 25

whose output is a function of only present inputs

Question 26

what is sequential logic

Answer 26

whose output is a function of present and past inputs

Question 27

what is XOR gate logic

Answer 27

if inputs disagree, output are HIGH

Question 28

what is XNOR gate logic

Answer 28

if inputs agree, output is HIGH

Question 29

What Variables have a 0 logic level value

Answer 29

A bar, B bar, C bar, D bar

Question 30

What Variables have a 1 logic level value

Answer 30

A, B, C, D

Question 31

How can you implement SOP expressions

Answer 31

Form the AND terms, Then OR the terms together

Question 32

what can multiple NAND gates do?

Answer 32

1 = inverter 2 = AND operation 3 = OR operation 4 = NOR operation

Question 33

what can multiple NOR gates do?

Answer 33

1 = inverter 2 = OR operation 3 = AND operation 4 = NAND operation

Question 34

what is a half adder

Answer 34

a digital circuit that performs binary addition of 2 one bit inputs and has two outputs of sum and carry out

Question 35

what is a full adder

Answer 35

digital circuit that performs binary addition of three bits ( 2 inputs and a carry In) and produces a sum and a carry-out bit (sum and carry out)

Question 36

what are parallel adders

Answer 36

full adders that are combined that can add binary numbers with multiple bits

Question 37

what are comparators

Answer 37

a device that compares the magnitudes of 2 binary numbers to determine the relationship between them

Question 38

function of IC comparators

Answer 38

provide outputs to indicate which of the numbers is larger or if they are equal

Question 39

function of decoders

Answer 39

a logic circuit that detects the presence of a specific combination of bits at its input

Question 40

function of encoders

Answer 40

accepts an active logic level on one of its inputs and converts it to a coded output (BCD or Binary)

Question 41

function of a multiplexer

Answer 41

selects one data line from two or more input lines and routes data from the selected line to the output

Question 42

function of the demultiplexers

Answer 42

switches data from one input line to two or more data lines depending on the select inputs

Question 43

what are latches

Answer 43

a temporary storage device that has 2 stable states

Question 44

what is an S-R latch

Answer 44

Set Reset Latch - can be made from NOR gate - responds to active HIGH inputs

Question 45

what are the input rules of an SR latch

Answer 45

R = 0, S = 1 : latch RESET R = 1, S = 0 = : latch SET Both 1 : invalid Both 0 : no change

Question 46

How is a SR active-high latch made stable

Answer 46

both inputs are low

Question 47

How is the SR active-high latch SET

Answer 47

a momentary HIGH signal is applied to the S input whilst R remains low

Question 48

How is the SR active-high latch RESET

Answer 48

a momentary HIGH signal is applied to the R input whilst S remains low

Question 49

How does a NAND constructed SR latch differ from a NOR constructed SR latch

Answer 49

latch responds to active-low inputs

Question 50

How is a SR active-low latch made stable

Answer 50

when both inputs are high

Question 51

How is the SR active-low latch SET

Answer 51

a momentary LOW signal is applied to the S bar input whilst R bar remains high

Question 52

How is the SR active-low latch RESET

Answer 52

a momentary LOW signal is applied to the R bar input whilst S bar remains high

Question 53

what is the Enable (EN) input

Answer 53

input within the gated SR latch that must be HIGH in order for the latch to respond to the S & R inputs

Question 54

what is a D latch

Answer 54

variation of the SR latch that combines the S & R inputs into a single D input - Q follows D when enable is active

Question 55

What are flip flops

Answer 55

a clocked device, in which only the clock edge determines when a new bit is entered - can be positive or negative edged

Question 56

what is a toggle

Answer 56

changes output until device becomes set again