ALU 101 Adder Circuits and Addition Logic 3

Question 1

How does an ALU typically perform binary subtraction using adder hardware?

Accepted Answer

Adding the two's complement of the subtrahend to the minuend

Answer

Using a separate dedicated subtractor circuit

Answer

Reversing all bits of both operands before adding

Answer

Applying a series of half adders in reverse order

Question 2

In a combined adder/subtractor circuit, what controls whether addition or subtraction is performed?

Accepted Answer

A mode select signal (M) that inverts B bits and sets carry-in

Answer

The carry-in value from the previous stage

Answer

The overflow flag from the status register

Answer

The zero flag output of the ALU

Question 3

What is the maximum sum when adding two 4-bit unsigned numbers?

Accepted Answer

30

Answer

15

Answer

16

Answer

31

Question 4

What binary result does adding 0101 and 0011 produce?

Accepted Answer

1000

Answer

0111

Answer

1010

Answer

0110

Question 5

In a BCD adder, what correction is applied to a digit sum that exceeds 9?

Accepted Answer

Add 6 (0110) to the result

Answer

Subtract 6 (0110) from the result

Answer

Add 10 (1010) to the result

Answer

Reset all bits to zero and set carry

Question 6

What distinguishes a parallel prefix adder (such as Kogge-Stone) from a standard carry lookahead adder?

Accepted Answer

It uses a tree structure to compute prefix generate/propagate in O(log n) depth

Answer

It uses a simpler, smaller circuit with fewer gates

Answer

It achieves lower power consumption at the cost of speed

Answer

It eliminates the need for propagate signals entirely

Question 7

When two positive signed numbers are added and the result has its sign bit set to 1, what condition has occurred?

Accepted Answer

Arithmetic overflow

Answer

Carry error

Answer

Borrow error

Answer

Arithmetic underflow