A 2-input NOR gate is equivalent to a ________.
Answer: B
Correct answer: negative-AND gate
By De Morgan's law \( (A+B)' = A'B' \), so a NOR gate gives 1 exactly when both inputs are 0 - that is, it is an AND gate for active-low inputs. Redrawing it with bubbles on the inputs and none on the output makes the equivalence visible.
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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?
Answer: C
Correct answer: 7
An OR output is LOW only when every input is LOW, and of the eight combinations of three inputs just one is all-zero. The remaining seven give a HIGH output.
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Fan-out is specified in terms of ________.
Answer: D
Correct answer: unit loads
Fan-out is expressed as the number of standard gate inputs, or unit loads, that one output can drive. It is a current limit underneath, but stating it in unit loads makes it directly usable when connecting gates of the same family.
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How many input combinations would a truth table have for a six-input AND gate?
Answer: C
Correct answer: 64
A truth table has \( 2^n \) rows for n inputs, so six inputs give \( 2^6 = 64 \).
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What is the circuit number of the IC that contains four two-input AND gates in standard TTL?
Answer: C
Correct answer: 7408
The 7408 is the quad two-input AND. Its neighbours in the family are the 7400 NAND, the 7402 NOR, the 7404 hex inverter and the 7432 OR.
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The terms "low speed" and "high speed," applied to logic circuits, refer to the ________.
Answer: C
Correct answer: propagation delay time
The speed of a logic family is measured by how long a change takes to travel from input to output, which is the propagation delay. Rise and fall times describe the edges of the signal, and clock speed is a property of the system rather than of the gate.
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The NOR logic gate is the same as the operation of the ________ gate with an inverter connected to the output.
Answer: A
Correct answer: OR
NOR is NOT-OR, so it is an OR gate with its output inverted.
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With regard to an AND gate, which statement is true?
Answer: C
Correct answer: If one input to a 2-input AND gate is HIGH, the output reflects the other input
Holding one AND input HIGH makes the output follow the other input exactly, which is how an AND gate is used as an enable. An AND gate may have more than two inputs but has only one output, and two inputs give four combinations, not eight.
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The term "hex inverter" refers to:
Answer: B
Correct answer: six inverters in a single package
The prefix counts the circuits in the package: hex is six. The 7404 hex inverter holds six independent one-input inverters, not one inverter with six inputs.
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How many inputs are on the logic gates of a 74HC21 IC?
Answer: D
Correct answer: 4
The 74HC21 is a dual four-input AND gate: two gates of four inputs each, which fits a 14-pin package with two pins to spare for supply and ground.
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