Digital Logic and Microprocessor
NEC Electrical and Electronic Engineering · 629 practice MCQs
The 'Digital Logic and Microprocessor' chapter is essential for understanding the foundational concepts of digital systems and microprocessor architecture. This chapter encompasses key topics such as flow control, encoding, and logic operations, which are crucial for the NEC licensing exam.
With 629 practice MCQs, this chapter equips you with the knowledge necessary to tackle complex questions on digital circuits and microprocessor functionalities. To prepare effectively, focus on mastering the concepts and practicing with the provided questions to enhance your problem-solving skills.
Sample questions with answers
1.Flow control prevents?
- A.Instruction fetch error
- B.Data overrun in serial communication
- C.Stack underflow
- D.ALU overflow
Why: Flow control in serial communication is essential to prevent data overrun, which occurs when the data being sent exceeds the buffer capacity, leading to loss of information.
2.When does the program counter get updated?
- A.Only after interrupt
- B.After fetching instruction
- C.After stack operation
- D.After ALU execution
Why: The program counter is updated after fetching an instruction to point to the next instruction in the sequence, ensuring the CPU processes instructions in the correct order.
3.What does an encoder produce?
- A.Binary code
- B.XOR
- C.One-hot
- D.Parity
Why: An encoder converts input signals into a binary code, which represents the activated input line in a compact binary format, making it easier for digital systems to process.
4.What is the 1’s complement of the binary number 1100?
- A.0000
- B.0011
- C.1111
- D.1101
Why: The 1's complement of a binary number is obtained by flipping all bits; thus, the 1's complement of 1100 is 0011, where each '1' becomes '0' and each '0' becomes '1'.
5.What does the RS232 standard specify?
- A.Parallel communication bus
- B.Pointer for stack management
- C.Voltage levels for serial communication
- D.Controller for DMA
Why: The RS232 standard defines the voltage levels for serial communication, ensuring that devices can communicate reliably by interpreting specific voltage ranges as binary signals.
6.What is the simplified result of A + AB?
- A.AB
- B.B
- C.A
- D.A+B
Why: The expression A + AB simplifies to A because if A is true, the entire expression is true regardless of B, demonstrating the redundancy of the AB term when A is present.
7.What is regarded as Logic HIGH in a CMOS circuit with a 5V supply?
- A.>1.2V
- B.>3.5V
- C.>4.8V
- D.>2V
Why: In a CMOS circuit with a 5V supply, a voltage greater than 3.5V is regarded as Logic HIGH, as it ensures reliable operation and recognition of a high state by the circuit.
8.How many select lines are needed for an 8:1 multiplexer?
- A.3
- B.2
- C.1
- D.4
Why: An 8:1 multiplexer requires 3 select lines because 2^3 = 8, allowing it to select one of the eight input lines uniquely.
9.How many 4:1 MUX units are needed to create a 16:1 MUX?
- A.4
- B.3
- C.5
- D.2
Why: To create a 16:1 multiplexer, you need 5 units of 4:1 multiplexers because you can combine them in stages: first to create 4 groups of 4:1, and then to select from those groups.
10.When does an overflow happen in an asynchronous binary counter?
- A.At half the count
- B.At minimum count
- C.In random states
- D.At max count + 1
Why: An overflow in an asynchronous binary counter occurs at max count + 1, where the counter exceeds its maximum representable value, causing it to wrap around to zero.
11.Why is two's complement considered fast?
- A.Sign bit inverted
- B.All bits inverted
- C.Two adders needed
- D.Single adder used
Why: Two's complement is considered fast because it allows for negative numbers to be represented and calculated using a single adder, simplifying the arithmetic operations in digital circuits.
12.How is memory hierarchy structured?
- A.Just by type
- B.By speed and cost
- C.Just by size
- D.Based on CPU design
Why: Memory hierarchy is structured by speed and cost, as faster memory types (like cache) are more expensive and are placed closer to the CPU, while slower, cheaper memory (like hard drives) is used for larger storage.
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Frequently asked questions
- What does flow control prevent?
- Flow control prevents data overflow and ensures proper data transmission in communication protocols.
- When does the program counter get updated?
- The program counter gets updated after each instruction fetch, pointing to the next instruction to be executed.
- What does an encoder produce?
- An encoder produces a binary code corresponding to the input signal, effectively converting it into a digital format.
- What is the 1’s complement of the binary number 1100?
- The 1’s complement of 1100 is 0011.
- How many select lines are needed for an 8:1 multiplexer?
- Three select lines are needed for an 8:1 multiplexer.