Digital Logic and Design MCQs with Answers
Practice important Digital Logic and Design MCQs with answers and explanations.
Chapter: 15
Q381:
In a BCD Adder, what happens if the result of the first Adder is a valid BCD number with no carry?
A. The second Adder adds a 6
B. The second Adder adds a 0
C. The result is discarded
D. The result is displayed without change
Correct Answer:
B
Chapter: 15
Q382:
What is the Boolean expression for detecting an invalid BCD number?
A. S3S2 + S3S1
B. S3S2 + S1S0
C. S3S1 + S2S0
D. S3S0 + S2S1
Correct Answer:
A
Chapter: 15
Q383:
How many 4-bit Parallel Adder Circuits are required for adding two BCD digits?
A. One
B. Two
C. Three
D. Four
Correct Answer:
B
Chapter: 15
Q384:
How is a 2-digit BCD Adder implemented?
A. Using two 4-bit Parallel Adders and invalid BCD detector circuits
B. Using a single 4-bit Parallel Adder
C. Using an 8-bit Adder
D. Using two 8-bit Adders
Correct Answer:
A
Chapter: 15
Q385:
What is the output of the 4-bit Adder when adding two BCD numbers if a Carry is generated?
A. The result is valid and no further action is needed
B. The result is adjusted by adding 6
C. The result is invalid
D. The result is adjusted by adding 0
Correct Answer:
B
Chapter: 15
Q386:
Which ICs are used in a 2-digit BCD Adder to handle invalid BCD digits?
A. 74LS283
B. 74LS00 and 74LS04
C. 74LS08 and 74LS32
D. 74LS02 and 74LS20
Correct Answer:
A
Chapter: 15
Q387:
How does subtraction work in digital systems using 2's complement?
A. By taking the 1's complement and adding 1
B. By directly subtracting the numbers
C. By converting the number to its positive form
D. By taking the 2's complement of the minuend
Correct Answer:
A
Chapter: 15
Q388:
In a 4-bit Adder/Subtracter unit, how is subtraction performed?
A. By setting the Add/Subtract control to 0
B. By setting the Add/Subtract control to 1
C. By setting the Carry In to 0
D. By using the AND gates only
Correct Answer:
B
Chapter: 15
Q389:
What is the function of the Carry In in a 4-bit Subtractor circuit?
A. To provide the carry bit for addition
B. To convert subtraction to addition
C. To handle the 2's complement operation
D. To adjust the result of subtraction
Correct Answer:
C
Chapter: 15
Q390:
How many 4-bit ALUs are needed to implement a 16-bit ALU?
A. Two
B. Four
C. Eight
D. Six
Correct Answer:
B
Chapter: 15
Q391:
What is the primary advantage of the Group-Carry Look-Ahead in ALUs?
A. It speeds up the carry propagation
B. It reduces the size of the ALU
C. It simplifies the ALU design
D. It allows for more operations in one ALU unit
Correct Answer:
A
Chapter: 15
Q392:
How does the 74XX181 ALU differ from the 74XX381 ALU?
A. It has more function select inputs
B. It provides ripple carry outputs
C. It has fewer arithmetic functions
D. It is only for 8-bit operations
Correct Answer:
A
Chapter: 15
Q393:
What is the purpose of using an 8-bit Adder/Subtracter Circuit?
A. To handle addition and subtraction of 8-bit numbers
B. To handle multiplication operations
C. To handle both 4-bit and 8-bit numbers
D. To simplify complex arithmetic operations
Correct Answer:
A
Chapter: 16
Q394:
Which ALU in a 16-bit ALU configuration generates Carry Out 8?
A. ALU0
B. ALU1
C. ALU2
D. ALU3
Correct Answer:
B
Chapter: 16
Q395:
How many ALUs are used to implement a 16-bit ALU without Look-Ahead Carry?
A. 2
B. 3
C. 4
D. 5
Correct Answer:
C
Chapter: 16
Q396:
What is the purpose of the Look-Ahead Carry Generator in a 16-bit ALU?
A. To increase delay
B. To eliminate carry propagation delay
C. To add extra ALUs
D. To generate extra outputs
Correct Answer:
B
Chapter: 16
Q397:
What does the G output of a 4-bit ALU indicate?
A. Carry In is zero
B. Carry Out is zero
C. Carry Out is generated regardless of Carry In
D. Carry is generated only if Carry In is active
Correct Answer:
C
Chapter: 16
Q398:
What is the function of the P output in a 4-bit ALU?
A. Indicates if Carry Out is generated regardless of Carry In
B. Indicates if Carry Out is generated only if Carry In is active
C. Indicates that no carry is generated
D. Indicates that all carry inputs are inactive
Correct Answer:
B
Chapter: 16
Q399:
The simplest and most commonly used Decoders are the ______ Decoders
A. n to 2n
B. (n-1) to 2n
C. (n-1) to (2n-1)
D. n to 2n-1
Correct Answer:
A
Chapter: 166
Q400:
The _______ Encoder is used as a keypad encoder.
A. 2-to-8 encoder
B. 4-to-16 encoder
C. BCD-to-Decimal
D. Decimal-to-BCD Priority
Correct Answer:
D