A 2-input gate that can be used to pass a digital waveform unchanged at certain times and inverted at other times is a(n) ________.
Answer: D
Correct answer: XOR gate
Holding one XOR input at 0 passes the other input unchanged, since \( 0\oplus X = X \); holding it at 1 inverts it, since \( 1\oplus X = X' \). That makes the XOR a controlled inverter, which no other two-input gate provides.
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When does the output of a NAND gate = 1?
Answer: A
Correct answer: Whenever a 0 is present at an input
NAND is the complement of AND. AND is 0 as soon as any input is 0, so NAND is 1 in that case, and it is 0 only when every input is 1.
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The number of input combinations for a 4-input gate is ________.
Answer: D
Correct answer: 16
Each input takes two values independently, so four inputs give \( 2^4 = 16 \) combinations.
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When does the output of a NOR gate = 0?
Answer: C
Correct answer: Whenever a 1 is present at an input
NOR is the complement of OR. OR is 1 as soon as any input is 1, so NOR is 0 in that case, and it is 1 only when every input is 0.
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