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UNIT 4 PASTPAPERS Information & Communication Technology Ishani Narahenpita

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2020 AL

MCQ

10. A block diagram of a sequential logic circuit is shown below, with one block labelled as "A" and the

other labelled as “B”.

Which of the following statements about the above block diagram are correct?

I - The block A is a combinational logic circuit.

II - The block B is a memory element.

III - Only the block A can be implemented using logic gates.

(1) Only I (2) Only II (3) Only I and II (4) Only I and III (5) All I, II and III

11. Consider the following logic circuit consisting of NAND gates:

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ESSAY

5. Consider the logic circuit shown in the figure, in which A, B and C are the inputs and Z is the output.

(a) Give the complete truth table for the given circuit.

(b) Using a Karnaugh map, derive a simplified sum-of-products (SOP) expression for the output Z.

(c) Using a Karnaugh map, derive a simplified product-of-sums (POS) expression for the output Z.

(d) Of the two expressions (SOP and POS) you obtained in (b) and (c) above, which one is better to

implement a more simplified logic circuit than the given logic circuit above? Explain your answer.

2019 AL

MCQ

• Consider the following logic circuit diagram to answer the questions 37 and 38:

37. Which of the following statements is/are correct about the above circuit?

I. It implements a full adder.

II. The logic function of S can be stated as S = A ⊕ B ⊕ Cin

III. The logic function of Cout can be stated as Cout = AB + BCin + ACin

(1) I only (2) II only (3) I and II only (4) II and III only (5) All I, II and III

38. Which of the following statements is/ are correct about the part of the circuit within the area

surrounded by the dotted line?

I - It implements a half adder.

II - It can be implemented using only AND and OR gates.

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III - It can be implemented using only NAND gates.

(l) I only (2) II only (3) III only (4) I and III only (5) All I, II and III

39. Consider the Karnaugh map shown below:

Which of the following is the: correct logic- expression that corresponds to the two marked segments on the

Karnaugh map?

ESSAY

l. The Boolean function known as the majority function takes n binary inputs and outputs 1 if a majority (at

least half) of the inputs are 1. otherwise, it outputs 0. Let us consider the case when n=3, which is the 3-input

majority function, whose inputs are A, B and C and the output is Z.

(a) Give the truth table for the 3-input majority function.

(b) Using Karnaugh map, derive a simplified Boolean expression for the output Z in the 3-input majority

function.

(c) Construct a logic circuit for the 3-inpui majority function using NAND gates only.

2018 AL

MCQ

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ESSAY

1. Suppose a logic circuit needs to be implemented for a digital system that has three inputs A, B and C and

one output Z. lts behaviour is as follows:

If the input C=1, the output Zhas the value of A.

If the input C=0, then output Z has the value of B.

(a) Obtain the truth table for the output Z.

(b) Write down either a sum of products (SOP) or a product of sums (POS) Boolean expression for Z.

(c) Simplify the Boolean expression for Z obtained in (b) above.

(d) Using the simplified expression in (c) above, construct a logic circuit for the system using either 2-

input NAND gates only or 2-input NOR gates only.

2017 AL

MCQ

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ESSAY

2016 AL

MCQ

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2015 AL

MCQ

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2014 AL

MCQ

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2013 AL

MCQ

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2012 AL

MCQ

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2011 AL

MCQ

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ESSAY

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MODEL PAPER QUESTIONS BY MINISTRY OF EDUCATION

2019 MODEL PAPER

MCQ

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ESSAY

In a fish tank, the health of goldfish depends on the pH value of the water, temperature and oxygen level of

the water in the tank. A sensor based control system is to be developed to make a healthy environment for the

survival of gold fish by maintaining appropriate levels of pH value, temperature and oxygen level of the water

of the fish tank. For this purpose a pH sensor (A), a temperature sensor (B) and an oxygen sensor (C) are to

be used to measure the pH level, temperature and oxygen level of the water respectively.

The following table shows the status of each sensor with the relevant binary values to be emitted by

the sensors.

The binary value '0' indicates the appropriate condition for the goldfish.

An automatic waterfall is connected to the fish tank. The waterfall starts automatically when the temperature

is not within the range or the oxygen level is less than the given value. The waterfall stops automatically to

save the power consumption when the temperature is at the range and the oxygen level is high. When the pH

value of the water is out of the given range, a bulb in the tank is lighted.

The start and stop states of the waterfall are represented by the binary values ''1'' and ''0'' respectively.

Construct a logic circuit to implement the function of the waterfall. Give the truth table and Boolean

expression.

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2013 MODEL PAPER

ESSAY

(a) (ii) Write down three advantages of manual data processing over electronic data processing.

(b) An aircraft is equipped with a quality control system with sensors that functions in accordance with temperature of

engine, pressure and rotation speed of shaft.

A warning bulb in pilot’s cabin is on when there is a risk and the risk levels are given below.

* When internal temperature is above 400 degrees centigrade. and

* Internal pressure is above 1.5Mpa or rotation speed of the shaft is less than 4000.

In a dangerous situation,

1.When the internal temperature is above 400 oC, ‘A’ temperature sensor is switched on automatically.

2 When the internal pressure is above 1.5Mpa, ‘B’ sensor is switched on automatically.

3.When the rotation speed of the shaft is less than 4000, ‘C’ sensor is switched on automatically.

Following table shows the input control system of the security alarm bulb and the relevant Boolean value.

(i) Design the circuit by using a combination of only AND, OR, NOT gates to implement the above control system.

(ii) Construct a truth table to represent the functionality of the above circuit.

(iii) Write a Boolean expression (not simplified) for the final output to represent the truth table.

(iv) Simplify the expression obtained in the above part (iii) using the Boolean laws or Karnaugh map.

(v) State with A, B and C, under which condition of the engine, the security alarm bulb is lit? (There may be several

possibilities)

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2012 MODEL PAPER

ESSAY

(i) Draw the truth table considering for every AND gate that output is 1.

(ii) Write down the Boolean expression for the output of the above circuit using a truth table.

(iii) Simplify the above expression using Boolean algebra or Karnaugh (K-Map).

(iv) Design the logic circuit for the answer you have obtained in above (iii).

(v) Convert the Boolean expression you obtained for the above part (ii) to Product of Sum (POS).

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2011 MODEL PAPER

ESSAY