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Universiti Malaysia PAHANG Engineering . Technology . Creativity

FACULTY OF MANUFACTURING ENGINEERING

FINAL EXAMINATION

COURSE

COURSE CODE

LECTURER

DATE

DURATION

SESSION/SEMESTER

PROGRAMME CODE

DIGITAL ELECTRONICS

BFM2313

NAFRIZUAN BIN MAT YAHYA

5 JANUARY 2012

3 HOURS

SESSION 2011/2012 SEMESTER I

BFM

INSTRUCTIONS TO CANDIDATE:

(a) Answer ALL questions.

(b) All answers to a new question should start on new page.

(c) All the calculations and assumptions must be clearly stated.

EXAMINATION REQUIREMENTS

NIL

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO

This examination paper consists of SEVEN (7) printed pages including front page.

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ANSWER ALL QUESTIONS

QUESTION 1 (20 MARKS)

(a) A storage tank system for a pancake syrup manufacturing process has four inputs A,

B, C, and D that control the whole tank system. The expression for the output Z, of

the system is given as:

Z = ABCD + ABCD + ABCD + ABCD+ ACD

i) Sketch the logic circuit represented by the output Z expression.

(2 marks)

ii) Develop a truth table for the output Z expression.

(5 marks)

iii) Reduce the function specified in truth table in Question 1 a (ii) to its minimum

SOP form by using a Karnaugh map.

(3 marks)

(b) The outputs of a Combinational Logic Circuits are only determined by the logical

function of their current input state, logic "0" or logic "1", at any given instant in time

as they have no feedback, and any changes to the signals being applied to their inputs

will immediately have an effect at the output. Figure 1 is a combinational logic circuit

with three inputs A, B, C, and an output X.

2

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A B

x DO

C

Figure 1: Combinational Logic Circuit

i) Implement the logic circuits in Figure 1 using only "NAND" gates.

(4 marks)

ii) Reiterate Question lii (a) using only "NOR" gates.

(4 marks)

iii) NAND gates and NOR gates are holding universal property. Why both gates

are known as Universal Gates?

(2 marks)

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QUESTION 2 (20 MARKS)

(a) The process of converting control objectives into a ladder logic program requires

structured thought. Boolean algebra provides the tools needed to analyze and design

these systems. By applying this technique design a car safety alarm system

considering four inputs:

• Door closed (D)

• Key In (K)

• Seat Pressure (S)

• Seat Belt Closed (B)

The alarm (A) should sound if:

• The key is in and the door is not closed, or

• The door is closed and the key is in and the driver is in the seat and the seat

belt is not closed.

(i) Specify the behavior of the system using a truth table.

(5 marks)

(ii) Derive the simplest sum of products (SOP).

(5 marks)

(iii) Draw the logic circuit diagram to accomplish the design.

(5 marks)

(iv) Implement the logic circuit diagram in Question 2a (iii) using either one of the

Universal Gates.

(5 marks)

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QUESTION 3 (20 MARKS)

(a) Figure 2, a dual NAND-gate circuit shown below is called a Set-Reset latch and has

the symbol shown at right. Complete the timing diagram by showing the waveforms

of Q and N assuming that Q is initially low.

SET

E L-T

N

- RESET R

'. N

RESET ^jj

Figure 2: Dual NAND-gate / Set-Reset Latch

SET

RESET

(5 marks)

(b) A general sequential circuit consists of a combinational logic section and a memory

section (flip-flops). Basic idea behind this type of design is to use flip flops to hold

the system's state and use combinational logic to make the system move from state to

state. By implementing this application, design a binary UP! DOWN counter with the

following sequence in Figure 3. The counter should be able to count up/down using J -

K flip-flops.

UP couNr

DOWN COITh.TF

Figure 3: UP! DOWN Sequence

(15 marks)

5

Data in

RIGHT! LEFT

CLK

Data out

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QUESTION 4 (20 MARKS)

(a) A 8-bit bidirectional shift register is shown below. A HIGH on this input enables a

shift to the right, and a LOW enables a shift to the left. Determine the state of the

register after each clock pulse for the RIGHT/LEFT control waveform given. Assume

that the register is initially storing the decimal numbers sixty-six in binary, with the

right-most position being the LSB. There is a LOW on the data-input line.

CLK JLJLrLJ1_FtJ_r1_iLTlJL

RIGHT/ LEFT

(6 marks)

(b) RAM or random access memory is the temporary memory that the computer uses to

perform its functions while being used. There are two major categories of RAM

which are:

• Static RAM (SRAM)

• Dynamic RAM (DRAM)

(i) Explain the differences between SRAM and DRAM

(6 marks)

(ii) Discuss the types of DRAM

(8 marks)

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QUESTION 5 (20 MARKS)

(a) A digital signal processor (DSP) is a type of microprocessor - one that is incredibly

fast and powerful. A DSP is unique because it processes data in real time. This real-

time capability makes a DSP perfect for applications where we won't tolerate any

delays. Digital cellular telephone is one of the applications how DSP has been used.

(i) Illustrate a simplified block diagram of a digital cellular phone.

(10 marks)

(ii) Describe the functions performed by the DSP in cellular application to

improve the reception and transmission of a voice signal.

(10 marks)

END OF EXAMINATION PAPER

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