# 4-Bit Parallel Adder/Subtractor – 2 MCQ’s

This set of Digital Circuits Multiple Choice Questions & Answers (MCQs) focuses on “4-Bit Parallel Adder/Subtractor – 2″.

1. Fast-look-ahead carry circuits found in most 4-bit full-adder circuits which ___________

a) Determine sign and magnitude

b) Reduce propagation delay

c) Add a 1 to complemented inputs

d) Increase ripple delay

2. One way to make a four-bit adder to perform subtraction is by ___________

a) Inverting the output

b) Inverting the carry-in

c) Inverting the B inputs

d) Grounding the B inputs

3. For a 4-bit parallel adder, if the carry-in is connected to a logical HIGH, the result is ___________

a) The same as if the carry-in is tied LOW since the least significant carry-in is ignored

b) That carry-out will always be HIGH

c) A one will be added to the final result

d) The carry-out is ignored

4. What distinguishes the look-ahead-carry adder?

a) It is slower than the ripple-carry adder

b) It is easier to implement logically than a full adder

c) It is faster than a ripple-carry adder

d) It requires advance knowledge of the final answer

5. What is one disadvantage of the ripple-carry adder?

a) The interconnections are more complex

b) More stages are required to a full adder

c) It is slow due to propagation time

d) All of the Mentioned

6. What is Manchester carry chain?

a) Is a chain of controlled inverter

b) Variation of a carry-lookahead adder

c) Variation of a full-adder

d) Variation of a ripple carry adder

7. Carry lookahead logic uses the concepts of ___________

a) Inverting the inputs

b) Complementing the outputs

c) Generating and propagating carries

d) Ripple factor

8. The carry propagation delay in 4-bit full-adder circuits ___________

a) Is cumulative for each stage and limits the speed at which arithmetic operations are performed

b) Is normally not a consideration because the delays are usually in the nanosecond range

c) Decreases in direct ratio to the total number of full-adder stages

d) Increases in direct ratio to the total number of full-adder stages but is not a factor in limiting the speed of arithmetic operations

9. The main disadvantage of Manchester carry chain is ___________

a) Ripple factor

b) Propagation delay

c) Capacitive load

d) Both propagation delay and capacitive load

10. Why is a fast-look-ahead carry circuit used in the 7483 4-bit full-adder?

a) To decrease the cost

b) To make it smaller

c) To slow down the circuit

d) To speed up the circuit

11. The summing outputs of a half or full-adder are designated by which Greek symbol?

a) Omega

b) Theta

c) Lambda

d) Sigma

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