Computer System (CSC 1033)

Outcome 1: Evaluate data representation and manipulation within a computer. Tutorial 2

2 | P a g e

Exercise 1f: Logic Gates

Choose the correct answers in the following questions.

1. What function is implemented by the circuit shown

x'y'+z

(x'+y')z

x'y'z

x'+y'+z

NA 2. What function is implemented by the circuit shown

x+y+z

x+y+z'

x'y'z

x'+y'+z'

NA 3. What function is implemented by the circuit shown

xz'+y

xz+y

x'z+y'

x'y'+y'z'

x'y'+y'z

3 | P a g e

4. Which gate is the following circuit equivalent to?

AND

OR

NAND

NOR

None of the above 5. Which of the following functions equals the function: f=x+yz' ?

x(y'+z)

x(y'+z)

(y+x)(z'+x)

(y+x')(x'+z')

NA 6. Any possible binary logic function can be implemented using only.

AND

OR

NOT

AA (anyone is sufficient)

NAND 7. The function in the following circuit is:

abcd

ab+cd

(a+b)(c+d)

a+b+c+d

(a'+b')(c'+d')

4 | P a g e

8. Given F=A'B+(C'+E)(D+F'), use de Morgan's theorem to find F'.

ACE'+BCE'+D'F

(A+B')(CE'D'F)

A+B+CE'D'F

ACE'+AD'F+B'CE'+B'D'F

NA 9. The function in the following circuit is:

x'+y'+z'

x+y+z

x'z'+y'z'

xy+z

z 10. Try Harder Simplify the following: {[(AB)'C]'D}'

(A'+B')C+D'

(A+B')C'+D'

A'+(B'+C')D

A'+B'+C'+D'

A+B+C+D

11. Y = (A.(A'C')'.B') + (A.B.C)

Simplify the above algebra equation then, draw the logic circuit for NOR gates only?

5 | P a g e

12. The output will be a LOW for any case when one or more inputs are zero in a(n):

A. OR gate B. NOT gate C. AND gate

D.NAND gate

13. If a signal passing through a gate is inhibited by sending a low into one of the inputs, and the output is HIGH, the gate is a(n):

A. AND B. NAND

C. NOR D.OR 14. A single transistor can be used to build which of the following digital logic

gates? A. AND gates B. OR gates C. NOT gates

D.NAND gates

15. The logic gate that will have HIGH or "1" at its output when any one of its inputs is HIGH is a(n):

A. OR gate

B. AND gate C. NOR gate D.NOT gate

16. How many NAND circuits are contained in a 7400 NAND IC?

A. 1 B. 2 C. 4

D.8

6 | P a g e

17. Exclusive-OR (XOR) logic gates can be constructed from what other logic gates?

A. OR gates only B. AND gates and NOT gates C. AND gates, OR gates, and NOT gates

D.OR gates and NOT gates

18. How many truth table entries are necessary for a four-input circuit?

A. 4 B. 8 C. 12 D.16

19. A NAND gate has:

A. LOW inputs and a LOW output B. HIGH inputs and a LOW output C. LOW inputs and a HIGH output

D.HIGH inputs and a HIGH output

20. The basic logic gate whose output is the complement of the input is the:

A. OR gate B. AND gate C. INVERTER gate

D.comparator

21. What input values will cause an AND logic gate to produce a HIGH output?

A. At least one input is HIGH. B. At least one input is LOW. C. All inputs are HIGH.

D.All inputs are LOW.

7 | P a g e

22. The output of an exclusive-OR (XOR) gate is 1 only when the inputs are different.

A. True

B.False

23. If the output of a gate is OFF when the inputs are the same, and ON when they are different, the gate must be an exclusive-OR.

A. True

B.False

24. The output of a NAND gate is the same as the inverted output of an AND gate.

A. True

B.False

25. Logic gate circuits contain predictable gate functions that open their outputs.

A. True B.False

26. If both inputs are required to be ON for the output to be ON, the gate must be an AND gate.

A. True

B.False

27. A NAND gate consists of an AND gate and an OR gate connected in series with each other.

A. True B.False

28. The exclusive-NOR (XNOR) gate is simply an OR gate followed by a NOT gate.

A. True B.False

8 | P a g e

29. A logic circuit whose output is LOW when at least one input is HIGH is a(n) _________ gate.

A. NOR

B. AND C. NAND D.exclusive-OR gate

30. The AND function can be used to ___________ and the OR function can be used to _____________.

A. enable, disable

B. disable, enable C. synchronize, energize D.detect, invert

31. The dependency notation " 1" inside a block stands for the ________ operation.

A. OR

B. XOR C. AND D.XNOR

32. If we use an AND gate to inhibit a signal from passing, one of the inputs must be _________.

A. LOW

B. HIGH C. inverted D.floating

33.

9 | P a g e

34. The output of one logic gate can be connected to the input of another. The example is a simple system using a NAND gate with a NOT gate.

Try the match table below to work out the output of the combination. You should find that it's the same as an AND gate:

35. Now try something a little more complex:

Can you work out the output? [Hint: label the output of each gate and work through logically.] Then try the match table below:

10 | P a g e

36. Look at this circuit below and try the match table given to show what the Output Q is

11 | P a g e

PASS YEARS EXAM 2007 SECTION B ANSWER ALL QUESTIONS (40 marks)

1. Construct Circuit from the Boolean Expression below.

a. (A . B) + (A . B) (5 marks)

2. Produce the Truth Table the Boolean Expression below. _

a. A . ( A + B ) (5 marks)

12 | P a g e

3. From circuit below find the Boolean Expression for Y and produce the truth table.

(7 marks)

4. From circuit below, produce the Truth Table and the Boolean expression for Y.

(7 marks)

Y

Y

13 | P a g e

PASS YEARS EXAM 2010 SECTION D ANSWER ALL QUESTIONS (30 marks)

1. Construct the truth table of f(x,y,z) = (x + y’)’ + (x + z’)’ (6 marks)

2. Implement J(A,B) = (A . B) + (A . B) using any types of logic gates (3 marks)

3. Using Boolean Algebra: a. Express and simplified the function for the following circuit: (5 marks)

14 | P a g e

b. Construct the truth table for the OUTPUT above. (5 marks)

4. Simplify f(x,y,z) = {[(x + y)’ + z]’ + y}’ by using Boolean Algebra. (5 marks) 5. Implement J(A,B, C, D) = A’.(C + D’) + [B + (C.D)]’ using any types of logic gates (6

marks)