Digital Logic and Design MCQs with Answers
Practice important Digital Logic and Design MCQs with answers and explanations.
Multiple Choice Questions
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
View Answer
A
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
View Answer
A
Q423: How many enable inputs does the 74XX138 Decoder have?
- A: 1
- B: 2
- C: 3
- D: 4
View Answer
C
Q424: Which output is active when all enable inputs of the 74XX138 Decoder are inactive?
- A: Y7
- B: Y0
- C: Y1
- D: Y2
View Answer
B
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
View Answer
D
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
View Answer
A
Q427: What is the active-high enable input in the 74XX138 Decoder?
- A: G1
- B: G2A
- C: G2B
- D: Y0
View Answer
A
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
View Answer
C
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'
View Answer
C
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
View Answer
A