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Chapter 2: Digital Logic and Microprocessor: MCQ Practice for the NEC License Exam (AItE)

This chapter contributes 10 of the 100 questions in the IT Engineering license exam. Below are its subtopics, what is usually tested, and 12 free sample questions with answers and explanations.

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Subtopics in this chapter

What is usually tested

Digital logic questions cover number systems and codes, logic gates, Boolean laws, Karnaugh maps, and the standard building blocks: multiplexers, decoders, encoders, adders, flip-flops, shift registers and counters. The microprocessor part asks about the internal architecture, registers, flags, addressing modes and simple instructions of the 8085 and 8086, memory types and interfacing, the 8255, serial transfer, DMA and the interrupt system.

Sample questions with answers

Try each question before opening the answer. These 12 are taken from the 150 questions for this chapter in the practice bank.

1. The minimum number of 2-input NAND gates required to implement an XOR gate is: (2.1 Digital logic)

  1. 3
  2. 4
  3. 5
  4. 6
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Answer: B. 4
XOR can be built with 4 NAND gates.

2. The hexadecimal number system has a base of: (2.1 Digital logic)

  1. 16
  2. 8
  3. 10
  4. 2
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Answer: A. 16
Hexadecimal uses sixteen symbols: 0 to 9 and A to F.

3. A multiplexer is a circuit that: (2.2 Combinational and arithmetic circuits)

  1. Converts a binary code into decimal outputs
  2. Routes a single input to one of several outputs
  3. Selects one of several inputs and passes it to a single output
  4. Stores one bit of data
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Answer: C. Selects one of several inputs and passes it to a single output
A multiplexer is also called a data selector.

4. A multiplexer with eight data inputs needs how many select lines? (2.2 Combinational and arithmetic circuits)

  1. Eight
  2. Two
  3. Four
  4. Three
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Answer: D. Three
n select lines can choose among 2^n inputs, and 2^3 = 8.

5. Which flip-flop toggles its output when both inputs are 1? (2.3 Sequential logic circuit)

  1. SR
  2. D
  3. JK
  4. Latch
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Answer: C. JK
A JK flip-flop toggles when J = K = 1.

6. The output of a sequential logic circuit depends on: (2.3 Sequential logic circuit)

  1. The number of gates only
  2. The present inputs only
  3. The supply voltage only
  4. The present inputs and the past state of the circuit
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Answer: D. The present inputs and the past state of the circuit
Sequential circuits contain memory elements; combinational circuits do not.

7. The Intel 8085 is a microprocessor of: (2.4 Microprocessor)

  1. 4-bit
  2. 8-bit
  3. 16-bit
  4. 32-bit
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Answer: B. 8-bit
8085 is an 8-bit microprocessor with a 16-bit address bus.

8. The Program Counter (PC) holds: (2.4 Microprocessor)

  1. The address of the next instruction
  2. The current instruction
  3. The result of the ALU
  4. The stack top
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Answer: A. The address of the next instruction
PC stores the memory address of the next instruction to be fetched.

9. A memory that loses its contents when the power is switched off is called: (2.5 Microprocessor system)

  1. Volatile memory
  2. Non-volatile memory
  3. Read-only memory
  4. Secondary memory
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Answer: A. Volatile memory
RAM is volatile; ROM, flash memory and magnetic disks are non-volatile.

10. Dynamic RAM needs periodic refreshing because each bit is stored as: (2.5 Microprocessor system)

  1. The state of a flip-flop
  2. Charge on a small capacitor, which leaks away
  3. A magnetised spot on a disk
  4. A blown or intact fuse
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Answer: B. Charge on a small capacitor, which leaks away
The charge must be restored every few milliseconds or the data is lost.

11. An interrupt is a signal that causes the processor to: (2.6 Interrupt operations)

  1. Suspend the current program and attend to a device or event
  2. Erase the contents of the memory
  3. Stop the system clock permanently
  4. Skip the next instruction and continue
Show answer
Answer: A. Suspend the current program and attend to a device or event
After the event has been serviced, the processor resumes the interrupted program.

12. The program that is executed in response to an interrupt is called: (2.6 Interrupt operations)

  1. A bootstrap loader
  2. An interrupt service routine
  3. An assembler directive
  4. A macro
Show answer
Answer: B. An interrupt service routine
Each interrupt source has its own service routine.

Practise this chapter

The full mock tests mix 10 questions from this chapter with 10 from each of the other nine, under the real 2-hour limit. Chapter practice mode lets you work through this chapter alone, untimed, with the explanation shown after every question.

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