## logic gates #### Discussion Question

General Questions

###### The output of an AND gate with three inputs, A, B, and C, is HIGH when ________.
 A A = 1, B = 1, C = 0 B A = 0, B = 0, C = 0 C A = 1, B = 1, C = 1 D A = 1, B = 0, C = 1
 ANS: C - A = 1, B = 1, C = 1

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###### If a 3-input NOR gate has eight input possibilities, how many of those possibilities will result in a HIGH output?
 A 1 B 2 C 7 D 8
 ANS: A - 1

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###### If a signal passing through a gate is inhibited by sending a LOW into one of the inputs, and the output is HIGH, the gate is a(n):
 A AND B NAND C NOR D OR
 ANS: B - NAND

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###### A device used to display one or more digital signals so that they can be compared to expected timing diagrams for the signals is a:
 A DMM B spectrum analyzer C logic analyzer D frequency counter
 ANS: C - logic analyzer

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###### When used with an IC, what does the term "QUAD" indicate?
 A 2 circuits B 4 circuits C 6 circuits D 8 circuits
 ANS: B - 4 circuits

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###### The output of an OR gate with three inputs, A, B, and C, is LOW when ________.
 A A = 0, B = 0, C = 0 B A = 0, B = 0, C = 1 C A = 0, B = 1, C = 1 D all of the above
 ANS: A - A = 0, B = 0, C = 0

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###### Which of the following logical operations is represented by the + sign in Boolean algebra?
 A inversion B AND C OR D complementation
 ANS: C - OR

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###### Output will be a LOW for any case when one or more inputs are zero for a(n):
 A OR gate B NOT gate C AND gate D NOR gate
 ANS: C - AND gate

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###### How many pins does the 4049 IC have?
 A 14 B 16 C 18 D 20
 ANS: B - 16

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###### Which of the following choices meets the minimum requirement needed to create specialized waveforms that are used in digital control and sequencing circuits?
 A basic gates, a clock oscillator, and a repetitive waveform generator B basic gates, a clock oscillator, and a Johnson shift counter C basic gates, a clock oscillator, and a DeMorgan pulse generator D basic gates, a clock oscillator, a repetitive waveform generator, and a Johnson shift counter
 ANS: A - basic gates, a clock oscillator, and a repetitive waveform generator

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###### TTL operates from a ________.
 A 9-volt supply B 3-volt supply C 12-volt supply D 5-volt supply
 ANS: D - 5-volt supply

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###### The output of a NOR gate is HIGH if ________.
 A all inputs are HIGH B any input is HIGH C any input is LOW D all inputs are LOW
 ANS: D - all inputs are LOW

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###### The switching speed of CMOS is now ________.
 A competitive with TTL B three times that of TTL C slower than TTL D twice that of TTL
 ANS: A - competitive with TTL

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###### The format used to present the logic output for the various combinations of logic inputs to a gate is called a(n):
 A Boolean constant B Boolean variable C truth table D input logic function
 ANS: C - truth table

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###### The power dissipation, PD, of a logic gate is the product of the ________.
 A dc supply voltage and the peak current B dc supply voltage and the average supply current C ac supply voltage and the peak current D ac supply voltage and the average supply current
 ANS: B - dc supply voltage and the average supply current

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###### A logic probe is again applied to the pins of a 7421 IC with the following results. Is there a problem with the circuit and if so, what is the problem? A Pin 6 should be ON. B Pin 8 should be ON. C Pin 8 should be pulsing. D no problem
 ANS: D - no problem

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###### If a 3-input AND gate has eight input possibilities, how many of those possibilities will result in a HIGH output?
 A 1 B 2 C 7 D 8
 ANS: A - 1

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###### The Boolean expression for a 3-input AND gate is ________.
 A X = AB B X = ABC C X = A + B + C D X = AB + C
 ANS: B - X = ABC

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###### A CMOS IC operating from a 3-volt supply will consume ________.
 A less power than a TTL IC B more power than a TTL IC C the same power as a TTL IC D no power at all
 ANS: A - less power than a TTL IC

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###### What does the small bubble on the output of the NAND gate logic symbol mean?
 A open collector output B tristate C The output is inverted. D none of the above
 ANS: C - The output is inverted.

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###### What are the pin numbers of the outputs of the gates in a 7432 IC?
 A 3, 6, 10, and 13 B 1, 4, 10, and 13 C 3, 6, 8, and 11 D 1, 4, 8, and 11
 ANS: C - 3, 6, 8, and 11

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###### The output of a NOT gate is HIGH when ________.
 A the input is LOW B the input is HIGH C power is applied to the gate's IC D power is removed from the gate's IC
 ANS: A - the input is LOW

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###### If the input to a NOT gate is A and the output is X, then ________.
 A X = A B C X = 0 D none of the above
 ANS: B - No answer description available for this question.

###### A logic probe is used to test the pins of a 7411 IC with the following results. Is there a problem with the chip and if so, what is the problem? A Pin 6 should be ON. B Pin 6 should be pulsing. C Pin 8 should be ON. D no problem
 ANS: B - Pin 6 should be pulsing.

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###### How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?
 A any one of the inputs B any two of the inputs C any three of the inputs D all four inputs
 ANS: D - all four inputs

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###### If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?
 A All inputs must be LOW. B All inputs must be HIGH. C At least one input must be LOW. D At least one input must be HIGH.
 ANS: C - At least one input must be LOW.

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###### Logically, the output of a NOR gate would have the same Boolean expression as a(n):
 A NAND gate immediately followed by an inverter B OR gate immediately followed by an inverter C AND gate immediately followed by an inverter D NOR gate immediately followed by an inverter
 ANS: B - OR gate immediately followed by an inverter

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###### A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?
 A The dim indication on the logic probe indicates that the supply voltage is probably low. B The output of the gate appears to be open. C The dim indication is the result of a bad ground connection on the logic probe. D The gate is a tristate device.
 ANS: B - The output of the gate appears to be open.

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###### What is the Boolean expression for a three-input AND gate?
 A X = A + B + C B X = A · B · C C A – B – C D A \$ B \$ C
 ANS: B - X = A · B · C

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###### Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?
 A NOR B NOT C NAND D AND
 ANS: A - NOR

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###### What is the difference between a 7400 and a 7411 IC?
 A 7400 has two four-input NAND gates; 7411 has three three-input AND gates B 7400 has four two-input NAND gates; 7411 has three three-input AND gates C 7400 has two four-input AND gates; 7411 has three three-input NAND gates D 7400 has four two-input AND gates; 7411 has three three-input NAND gates
 ANS: B - 7400 has four two-input NAND gates; 7411 has three three-input AND gates

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###### Write the Boolean expression for an inverter logic gate with input C and output Y.
 A Y = C B Y = ANS: B - Y = No answer description available for this question.

###### The output of an exclusive-OR gate is HIGH if ________.
 A all inputs are LOW B all inputs are HIGH C the inputs are unequal D none of the above
 ANS: C - the inputs are unequal

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###### A clock signal with a period of 1 s is applied to the input of an enable gate. The output must contain six pulses. How long must the enable pulse be active?
 A Enable must be active for 0 s. B Enable must be active for 3 s. C Enable must be active for 6 s. D Enable must be active for 12 s.
 ANS: C - Enable must be active for 6 s.

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###### The AND function can be used to ________ and the OR function can be used to ________ .
 A enable, disable B disable, enable C enable or disable, enable or disable D detect, invert
 ANS: C - enable or disable, enable or disable

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###### One advantage TTL has over CMOS is that TTL is ________.
 A less expensive B not sensitive to electrostatic discharge C faster D more widely available
 ANS: B - not sensitive to electrostatic discharge

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###### A 2-input NOR gate is equivalent to a ________.
 A negative-OR gate B negative-AND gate C negative-NAND gate D none of the above
 ANS: B - negative-AND gate

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###### If a 3-input OR gate has eight input possibilities, how many of those possibilities will result in a HIGH output?
 A 1 B 2 C 7 D 8
 ANS: C - 7

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###### Fan-out is specified in terms of ________.
 A voltage B current C wattage D unit loads

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###### How many input combinations would a truth table have for a six-input AND gate?
 A 32 B 48 C 64 D 128
 ANS: C - 64

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###### What is the circuit number of the IC that contains four two-input AND gates in standard TTL?
 A 7402 B 7404 C 7408 D 7432
 ANS: C - 7408

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###### The terms "low speed" and "high speed," applied to logic circuits, refer to the ________.
 A rise time B fall time C propagation delay time D clock speed
 ANS: C - propagation delay time

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###### The NOR logic gate is the same as the operation of the ________ gate with an inverter connected to the output.
 A OR B AND C NAND D none of the above
 ANS: A - OR

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###### The logic expression for a NOR gate is ________.
 A B C D ANS: D - No answer description available for this question

###### With regard to an AND gate, which statement is true?
 A An AND gate has two inputs and one output. B An AND gate has two or more inputs and two outputs. C If one input to a 2-input AND gate is HIGH, the output reflects the other input. D A 2-input AND gate has eight input possibilities.
 ANS: C - If one input to a 2-input AND gate is HIGH, the output reflects the other input.

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###### The term "hex inverter" refers to:
 A an inverter that has six inputs B six inverters in a single package C a six-input symbolic logic device D an inverter that has a history of failure
 ANS: B - six inverters in a single package

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###### How many inputs are on the logic gates of a 74HC21 IC?
 A 1 B 2 C 3 D 4
 ANS: D - 4

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###### The basic logic gate whose output is the complement of the input is the:
 A OR gate B AND gate C inverter D comparator
 ANS: C - inverter

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###### When reading a Boolean expression, what does the word "NOT" indicate?
 A the same as B inversion C high D low
 ANS: B - inversion

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###### The output of an exclusive-NOR gate is HIGH if ________.
 A the inputs are equal B one input is HIGH, and the other input is LOW C the inputs are unequal D none of the above
 ANS: A - the inputs are equal

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###### How many AND gates are found in a 7411 IC?
 A 1 B 2 C 3 D 4
 ANS: C - 3

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###### Which of the following equations would accurately describe a four-input OR gate when A = 1, B = 1, C = 0, and D = 0?
 A 1 + 1 + 0 + 0 = 01 B 1 + 1 + 0 + 0 = 1 C 1 + 1 + 0 + 0 = 0 D 1 + 1 + 0 + 0 = 00
 ANS: B - 1 + 1 + 0 + 0 = 1

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###### What is the name of a digital circuit that produces several repetitive digital waveforms?
 A an inverter B an OR gate C a Johnson shift counter D an AND gate
 ANS: C - a Johnson shift counter

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###### The basic types of programmable arrays are made up of ________.
 A AND gates B OR gates C NAND and NOR gates D AND gates and OR gates
 ANS: D - AND gates and OR gates

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###### The logic gate that will have HIGH or "1" at its output when any one (or more) of its inputs is HIGH is a(n):
 A OR gate B AND gate C NOR gate D NOT operation
 ANS: A - OR gate

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###### CMOS IC packages are available in ________.
 A DIP configuration B SOIC configuration C DIP and SOIC configurations D neither DIP nor SOIC configurations
 ANS: C - DIP and SOIC configurations

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###### Which of the following is not a basic Boolean operation?
 A OR B NOT C AND D FOR
 ANS: D - FOR

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###### Which of the following gates is described by the expression ?
 A OR B AND C NOR D NAND
 ANS: D - NAND

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###### What is the Boolean expression for a four-input OR gate?
 A Y = A + B + C + D B Y = A· B · C · D C Y = A – B – C – D D Y = A \$ B \$ C \$ D
 ANS: A - Y = A + B + C + D

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###### How many truth table entries are necessary for a four-input circuit?
 A 4 B 8 C 12 D 16
 ANS: D - 16

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###### How many entries would a truth table for a four-input NAND gate have?
 A 2 B 8 C 16 D 32
 ANS: C - 16

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###### The Boolean expression for a 3-input OR gate is ________.
 A X = A + B B X = A + B + C C X = ABC D X = A + BC
 ANS: B - X = A + B + C

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###### From the truth table for a three-input NOR gate, what is the only condition of inputs A, B, and C that will make the output X high?
 A A = 1, B = 1, C = 1 B A = 1, B = 0, C = 0 C A = 0, B = 0, C = 1 D A = 0, B = 0, C = 0
 ANS: D - A = 0, B = 0, C = 0

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###### The logic gate that will have a LOW output when any one of its inputs is HIGH is the:
 A NAND gate B AND gate C NOR gate D OR gate
 ANS: C - NOR gate

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###### The output of a NAND gate is LOW if ________.
 A all inputs are LOW B all inputs are HIGH C any input is LOW D any input is HIGH
 ANS: B - all inputs are HIGH

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