What does the `NEG` instruction in 8086 perform?

Calculates two's complement of operand

Calculates one's complement of operand

What is the minimum number of flip-flops needed for a MOD-12 counter?

Four flip-flops are needed for a MOD-12 counter.

What is the hexadecimal representation of the binary number 1010?

The hexadecimal representation of the binary number 1010 is A.

What does the complement law state about A · A'?

The complement law states that A · A' = 0.

How many half adders are needed to create a full adder?

Two half adders are needed to create a full adder.

In an 8-bit signed 2’s complement, what does the binary 10000000 signify?

In an 8-bit signed 2’s complement, the binary 10000000 signifies -128.

Digital Logic and Microprocessor

NEC Computer Engineering · 1,774 practice MCQs

The 'Digital Logic and Microprocessor' chapter is crucial for aspiring engineers preparing for the NEC licensing exam. It covers essential concepts such as flip-flops, counters, adders, and binary number systems, which form the foundation of digital systems.

Understanding these topics is vital not only for passing the exam but also for practical applications in the field of computer engineering. To excel, utilize our 1774 practice MCQs to reinforce your knowledge and gain confidence in your problem-solving skills.

Sample questions with answers

1.What is the minimum number of flip-flops needed for a MOD-12 counter?
- A.6
- B.5
- C.3
- D.4
Why: A MOD-12 counter requires enough flip-flops to represent 12 unique states. The formula for the number of flip-flops needed is log2(N), where N is the modulus. For 12, log2(12) is approximately 3.58, so we round up to 4 flip-flops.
2.What is the hexadecimal representation of the binary number 1010?
- A.A
- B.B
- C.C
- D.8
Why: The binary number 1010 corresponds to the decimal number 10. In hexadecimal, the decimal number 10 is represented as 'A'. Therefore, the correct answer is A.
3.What does the complement law state about A · A'?
- A.0
- B.1
- C.A
- D.A'
Why: The complement law states that the product of a variable and its complement is always 0. This means A · A' results in 0, confirming that the correct answer is 0.
4.How many half adders are needed to create a full adder?
- A.3
- B.4
- C.2
- D.1
Why: A full adder can be constructed using two half adders and an OR gate. The two half adders are used to handle the two bits being added and the carry-in bit, making the correct answer 2.
5.In a synchronous 3-bit counter, how many flip-flops can change at the same time?
- A.Only 1
- B.Up to 3
- C.Up to 2
- D.None
Why: In a synchronous 3-bit counter, all flip-flops are clocked simultaneously, meaning they can all change states at the same time. Therefore, the answer is 'Up to 3'.
6.In 8-bit signed 2’s complement, what does the binary 10000000 signify?
- A.0
- B.-127
- C.-128
- D.+128
Why: In 8-bit signed 2's complement representation, the binary 10000000 represents -128. This is because the most significant bit indicates the sign, and the value corresponds to -128 in decimal.
7.Which type of adder allows for carry precomputation across blocks?
- A.CSA
- B.Ripple Carry
- C.Carry Select Adder
- D.Half Adder
Why: The Carry Select Adder allows for carry precomputation across different blocks, which speeds up the addition process by reducing carry propagation time, making it the correct answer.
8.In a linear feedback shift register (LFSR), the feedback connection utilizes:
- A.OR gates
- B.XOR gates
- C.Only flip-flops
- D.AND gates
Why: In a linear feedback shift register, the feedback connection is made using XOR gates. This allows for the necessary feedback to generate pseudo-random sequences.
9.What is the 8-bit signed representation of 10000001?
- A.-126
- B.+126
- C.-127
- D.+127
Why: The binary number 10000001 in 8-bit signed 2's complement represents -127, as it has the most significant bit set to 1, indicating a negative number.
10.What does the modulus of a counter indicate?
- A.Propagation cycles
- B.Total unique states
- C.Frequency of clock input
- D.Delay in output
Why: The modulus of a counter indicates the total unique states it can represent before returning to the initial state, which is essential for understanding its operation.
11.Which adder achieves a log2(n) stage depth?
- A.Carry Save Adder
- B.Carry Lookahead Adder
- C.Ripple Carry Adder
- D.Parallel Prefix Adder
Why: The Parallel Prefix Adder achieves a log2(n) stage depth due to its structure, which allows for faster addition by processing carries in parallel.
12.What does the `NEG` instruction in 8086 perform?
- A.Shifts operand to the left
- B.Calculates one's complement of operand
- C.Shifts operand to the right
- D.Calculates two's complement of operand
Why: The `NEG` instruction in the 8086 assembly language calculates the two's complement of the operand, effectively negating its value.

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Frequently asked questions

What is the minimum number of flip-flops needed for a MOD-12 counter?: Four flip-flops are needed for a MOD-12 counter.
What is the hexadecimal representation of the binary number 1010?: The hexadecimal representation of the binary number 1010 is A.
What does the complement law state about A · A'?: The complement law states that A · A' = 0.
How many half adders are needed to create a full adder?: Two half adders are needed to create a full adder.
In an 8-bit signed 2’s complement, what does the binary 10000000 signify?: In an 8-bit signed 2’s complement, the binary 10000000 signifies -128.