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Microprocessors and microcontrollers: board exam questions with solutions

On the ECE exam under Electronics Engineering. Try each question before you open its solution, then practise with fresh numbers below: 1 computed question type on this topic.

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Build it in the lab

Monitoring a supply rail with the ADC · Analog in, PWM out: the same circuits on a live bench, with meters you can move.

Questions

1. A processor has a 16-bit address bus and byte-addressable memory. How many memory locations can it address directly?

  1. 16,384
  2. 32,768
  3. 1,048,576
  4. 65,536
Show the answer and solution

Answer: D. 65,536

2¹⁶ = 65,536 locations (64 KB).

2. How many address lines are needed to select every location in a 32K × 8 memory chip?

  1. 8
  2. 13
  3. 15
  4. 32
Show the answer and solution

Answer: C. 15

32K = 32 × 1024 = 2¹⁵, so 15 address lines are needed; the ×8 is the data width.

3. How many 8K × 8 memory chips are needed to build a 64 KB (64K × 8) memory?

  1. 4
  2. 8
  3. 16
  4. 2
Show the answer and solution

Answer: B. 8

64K/8K = 8 chips, each supplying 8 KB of the address space.

4. What does the program counter (PC) of a microprocessor hold?

  1. The address of the next instruction to be fetched
  2. The result of the last ALU operation
  3. The number of instructions executed so far
  4. The address of the top of the stack
Show the answer and solution

Answer: A. The address of the next instruction to be fetched

The PC points to the next instruction; it increments after each fetch and is reloaded by jumps, calls and returns.

5. In what order is data retrieved from a stack?

  1. First in, first out (FIFO)
  2. By ascending address only
  3. Randomly, by index
  4. Last in, first out (LIFO)
Show the answer and solution

Answer: D. Last in, first out (LIFO)

PUSH places data on top and POP removes the most recently pushed item, so the stack is LIFO.

6. An 8 KB memory block begins at address 4000H. What is its last address?

  1. 5000H
  2. 47FFH
  3. 5FFFH
  4. 6000H
Show the answer and solution

Answer: C. 5FFFH

8 KB = 2000H bytes, so the block spans 4000H to 4000H + 2000H − 1 = 5FFFH.

7. A processor runs from an 8 MHz clock. How long does an instruction that takes 4 clock cycles require?

  1. 2.0 µs
  2. 0.5 µs
  3. 32 µs
  4. 0.125 µs
Show the answer and solution

Answer: B. 0.5 µs

One cycle = 1/8 MHz = 0.125 µs; 4 × 0.125 µs = 0.5 µs.

8. An 8-bit processor adds 9CH and 75H. What are the 8-bit result and the carry flag?

  1. 11H with carry = 1
  2. 11H with carry = 0
  3. F1H with carry = 0
  4. EFH with carry = 1
Show the answer and solution

Answer: A. 11H with carry = 1

9CH + 75H = 111H (156 + 117 = 273). It exceeds FFH, so the register holds 11H and the carry flag is set.

Worked examples with computed numbers

These numbers are fixed on this page; in practice they change every time.

9. What is the step size (1 LSB) of a 10-bit ADC with a 4.096 V reference?

  1. 410 mV
  2. 8.01 mV
  3. 4 mV
  4. 8 mV
Show the answer and solution

Answer: C. 4 mV

LSB = Vref/2ⁿ = 4.096/1024 = 4 mV.

Other topics in the same subjects

DC circuits · AC circuits · Transients (RC, RL, RLC) · Semiconductors and diodes · BJT and FET circuits · Operational amplifiers · Oscillators and feedback · Power electronics · Digital electronics · Control systems · Instrumentation and measurement

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