**UNIVERSITY EXAMINATIONS: 2017/2018**

**EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE IN**

**INFORMATION COMMUNICATION TECHNOLOGY**

**BCT 1305 SEMICONDUCTOR AND DIGITAL LOGIC**

**FULL TIME/PART TIME**

**DATE: DECEMBER, 2017 TIME: 2 HOURS**

**INSTRUCTIONS: Answer Question One & ANY OTHER TWO questions.**

**QUESTION ONE [30 MARKS]**

a) Name the gates in the diagrams below. For each give the truth table. [10 Marks]

b) Using diagrams explain the difference between N-type and P-type Semiconductors[6 Marks]

c) Describe the difference between a logic gate and a flip-flop. Give a symbol for each

[4 Marks]

d) Give the symbols for the XNOR and NAND gates [2 Marks]

e) Give the difference between the semiconductor and conductor materials [2 Marks]

f) Define the terms below

i. doping

ii. p-n junction

iii. forward bias

iv. free electrons [4 Marks]

**QUESTION TWO**

a) Define the terms digital and analogue. Clearly show the difference. Neat waveform diagrams

may be used [6

Marks]

b) Perform the following number conversions [8 Marks]

i. 34.6710 = _______________2

ii. 2B.3E16 = ______________2

iii. 10010.10112 = __________8

iv. 26.78 = ________________2

c) List two applications of computer systems [2 Marks]

d) Give two advantages of digital transmission over the cheaper analogue transmission

[2 Marks]

**QUESTION THREE**

a) Define the following as used with digital logic [4 Marks]

i. Sequential logic

ii. Counter

iii. Register

iv. Multiplexer

b) Using D-flipflops construct a 4-bit register [4 Marks]

c) Name two main types of counters [2 Marks]

d) Give the circuit and operation of a comparator circuit [6 Marks]

e) Give any two number codes and their use [4 Marks]

**QUESTION FOUR**

a) Define the term combination logic [2 Marks]

b) Minimise the following logic expressions using the K-map [9 Marks]

i. F(ABC) = m(0,1,2,5,7) Ʃ

ii. F(ABCD) = m(0,1,3,4,6,7,8,10,12,13,15) Ʃ

iii. F(ABC) = m(1,3,5,6,7) Ʃ

c) Apart from data storage give three other application of register circuits. Illustrate each with a

block diagram [6 Marks]

**QUESTION FIVE**

a) Given the truth tables below, minimise the output using a k-map and give the outputs X and Z.

Draw the circuits. [10 Marks]

A B C X Z

0 0 0 0 1

0 0 1 0 0

0 1 0 1 1

0 1 1 1 1

1 0 0 1 1

1 0 1 0 0

1 1 0 1 1

1 1 1 1 0

b) Give the difference between combinational and sequential logic [3 Marks]

c) A circuit compares two bits A and B, and gives two outputs X{A>B} and Y{A<B}. Draw the

truth table and the logic circuit [7 Marks]