Jamia Millia Islamia MCA Digital Logic Previous Year Questions (PYQs) – Page 1 of 2
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The expression of an XOR gate is —
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Solution
The logical expression for XOR (Exclusive OR) is true when inputs are different,
therefore its expression is $A'B + AB'$.
Multiply 1101 by 1011 (binary multiplication):
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Solution
$1101_2 = 13_{10}$
$1011_2 = 11_{10}$
$13 \times 11 = 143_{10}$
Convert $143_{10}$ to binary:
$143_{10} = 10001111_2$
Minimum number of two-input NAND gates used to perform the function of two-input OR gate is
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Solution
$A + B = \text{NAND}(\text{NAND}(A,A), \text{NAND}(B,B))$.
Hence, $3$ NAND gates required.
$\boxed{3}$
Which logic gate outputs true only if both inputs are true?
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Solution
| A | B | Output |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
What is the purpose of a multiplexer ?
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Solution
A multiplexer (MUX) selects one of many input signals and forwards it to a single output line using control signals.
Which logic gate is used to perform the NOT operation on an input ?
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Solution
A NOT operation inverts the input. Among the options, NOR can act as a NOT gate when one input is fixed at 0.
The universal gate is …
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Solution
NAND and NOR are universal; here option is NAND.
The inputs of a NAND gate are connected together. The resulting circuit is
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Solution
NAND with tied inputs gives ¬(A·A)=¬A → NOT gate.
____ truth table entries are necessary for a four-input circuit.
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Solution
Number of input combinations = 2^4 = 16.
Which of the following logic gates produces true only when one input is true and the other is false?
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Solution
OR gate outputs 1 only when inputs are different.
| A | B | Output |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
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