Digital Logic and Design MCQs with Answers
Practice important Digital Logic and Design MCQs with answers and explanations.
Chapter: 16
Q421:
What is the function of the NOT gates in the 74LS139 MSI chip circuit?
A. To convert active-high outputs to active-low outputs
B. To convert active-low outputs to active-high outputs
C. To disable the entire circuit
D. To simplify the input load
Correct Answer:
A
Chapter: 17
Q422:
What is the primary function of a 74XX138 3-to-8 Decoder?
A. Convert 3-bit input to 8-bit output
B. Convert 2-bit input to 4-bit output
C. Convert 4-bit input to 16-bit output
D. Convert 8-bit input to 3-bit output
Correct Answer:
A
Chapter: 17
Q423:
How many enable inputs does the 74XX138 Decoder have?
A. 1
B. 2
C. 3
D. 4
Correct Answer:
C
Chapter: 17
Q424:
Which output is active when all enable inputs of the 74XX138 Decoder are inactive?
A. Y7
B. Y0
C. Y1
D. Y2
Correct Answer:
B
Chapter: 17
Q425:
In the 74XX138 Decoder function table, what is the output when G1 = 1, G2A = 0, G2B = 1, A = 1, B = 0, C = 1?
A. Y4
B. Y5
C. Y6
D. Y7
Correct Answer:
D
Chapter: 17
Q426:
What is the purpose of cascading two 74XX138 Decoders?
A. To increase the number of outputs
B. To reduce the power consumption
C. To decrease the input lines
D. To simplify the circuit design
Correct Answer:
A
Chapter: 17
Q427:
What is the active-high enable input in the 74XX138 Decoder?
A. G1
B. G2A
C. G2B
D. Y0
Correct Answer:
A
Chapter: 17
Q428:
How does the 74XX138 Decoder handle invalid input conditions?
A. All outputs are low
B. All outputs are high
C. Outputs depend on the enable inputs
D. Outputs are undefined
Correct Answer:
C
Chapter: 17
Q429:
What Boolean expression is represented by the 3-to-8 Decoder output Y5 when A = 1, B = 0, C = 1?
A. A'B'C
B. AB'C'
C. A'BC
D. ABC'
Correct Answer:
C
Chapter: 17
Q430:
What is the function of the Ripple Blanking Input (RBI) in the 74LS47 7-Segment Decoder?
A. It blanks out the display of leading zeros
B. It tests all segments for operation
C. It enables all segments to display
D. It cascades multiple decoders
Correct Answer:
A
Chapter: 17
Q431:
In an 8-to-3 Binary Encoder, what output is produced when input I4 is active?
A. zero
B. 1
C. 10
D. 100
Correct Answer:
C
Chapter: 17
Q432:
How does a Priority Encoder differ from a Binary Encoder?
A. It handles multiple active inputs by prioritizing
B. It produces a binary output
C. It has fewer inputs than a Binary Encoder
D. It has higher propagation delay
Correct Answer:
A
Chapter: 17
Q433:
What is the function of the Enable Output (EO) in a priority encoder?
A. To cascade multiple encoders
B. To activate the highest priority input
C. To reset the encoder
D. To disable the outputs
Correct Answer:
A
Chapter: 17
Q434:
What is the output of a Decimal-to-BCD Encoder when decimal 5 is input?
A. zero
B. 101
C. 1010
D. 1111
Correct Answer:
B
Chapter: 17
Q435:
In a 4-to-1 Multiplexer, what happens when S1 = 1 and S0 = 0?
A. Input I0 is selected
B. Input I1 is selected
C. Input I2 is selected
D. Input I3 is selected
Correct Answer:
C
Chapter: 17
Q436:
What is the primary use of a multiplexer in a computer system?
A. To route data from multiple sources to a single destination
B. To convert binary data to decimal
C. To perform arithmetic operations
D. To store data
Correct Answer:
A
Chapter: 18
Q437:
What is the primary function of the 74X157 2-input, 4-bit multiplexer?
A. Route 4-bit data from one source to another
B. Route 2-bit data from multiple sources
C. Route 8-bit data from one source to another
D. Route 4-bit data from multiple sources
Correct Answer:
A
Chapter: 18
Q438:
How many sets of 4-bit inputs does the 74X157 multiplexer have?
A. 1
B. 2
C. 3
D. 4
Correct Answer:
B
Chapter: 18
Q439:
What happens when the select input (S) of the 74X157 multiplexer is set to 0?
A. The first set of 4-bit inputs is connected to the output
B. The second set of 4-bit inputs is connected to the output
C. The output is disabled
D. The output is connected to ground
Correct Answer:
A
Chapter: 18
Q440:
In the 74X157 multiplexer, what does the active-low G input control?
A. Enables or disables the multiplexer
B. Selects between the two sets of 4-bit inputs
C. Connects the output to ground
D. Sets the select input to high
Correct Answer:
A