# Education In Pakistan

## VU CS302- Digital Logic Design (Session – 4) FINALTERM EXAMINATION Spring 2010

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FINALTERM EXAMINATION

Spring 2010

CS302- Digital Logic Design (Session – 4)

Time: 90 min

Marks: 58

For Teacher’s Use Only

Q

No.

1 2 3 4 5 6 7 8 Total

Marks

Q No. 9 10 11 12 13 14 15 16

Marks

Q No. 17 18 19 20 21 22 23 24

Marks

Q No. 25 26 27 28 29 30 31 32

Marks

Q No. 33 34 35 36

Marks

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Question No: 1 ( Marks: 1 ) – Please choose one

The ANSI/IEEE Standard 754 defines a __________Single-Precision Floating Point

format for binary numbers.

► 8-bit

► 16-bit

► 32-bit

► 64-bit

Question No: 2 ( Marks: 1 ) – Please choose one

The decimal “17” in BCD will be represented as _________

► 11101

► 11011

► 10111

► 11110

Question No: 3 ( Marks: 1 ) – Please choose one

The basic building block for a logical circuit is _______

► A Flip-Flop

► A Logical Gate

► None of given options

Question No: 4 ( Marks: 1 ) – Please choose one

The output of the expression F=A.B.C will be Logic ________ when A=1, B=0,

C=1.

► Undefined

► One

► Zero

► No Output as input is invalid.

Question No: 5 ( Marks: 1 ) – Please choose one

________ is invalid number of cells in a single group formed by the adjacent cells in Kmap

► 2

► 8

12

► 16

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Question No: 6 ( Marks: 1 ) – Please choose one

The PROM consists of a fixed non-programmable ____________ Gate array configured

as a decoder.

AND

► OR

► NOT

► XOR

Question No: 7 ( Marks: 1 ) – Please choose one

___________ is one of the examples of synchronous inputs.

J-K input

► EN input

► Preset input (PRE)

► Clear Input (CLR)

Question No: 8 ( Marks: 1 ) – Please choose one

___________ is one of the examples of asynchronous inputs.

► J-K input

► S-R input

D input

► Clear Input (CLR)

Question No: 9 ( Marks: 1 ) – Please choose one

The _____________ input overrides the ________ input

Asynchronous, synchronous

► Synchronous, asynchronous

► Preset input (PRE), Clear input (CLR)

► Clear input (CLR), Preset input (PRE)

Question No: 10 ( Marks: 1 ) – Please choose one

__________occurs when the same clock signal arrives at different times at different

clock inputs due to propagation delay.

► Race condition

Clock Skew

► Ripple Effect

► None of given options

Question No: 11 ( Marks: 1 ) – Please choose one

Consider an up/down counter that counts between 0 and 15, if external input(X) is “0”

the counter counts upward (0000 to 1111) and if external input (X) is “1” the counter

counts downward (1111 to 0000), now suppose that the present state is “1100” and X=1,

the next state of the counter will be ___________

.

► 0000

1101

► 1011

► 1111

Question No: 12 ( Marks: 1 ) – Please choose one

In a state diagram, the transition from a current state to the next state is determined by

Current state and the inputs

► Current state and outputs

► Previous state and inputs

► Previous state and outputs

Question No: 13 ( Marks: 1 ) – Please choose one

________ is used to minimize the possible no. of states of a circuit.

State assignment

► State reduction

► Next state table

► State diagram

Question No: 14 ( Marks: 1 ) – Please choose one

________ is used to simplify the circuit that determines the next state.

State diagram

► Next state table

► State reduction

► State assignment

Question No: 15 ( Marks: 1 ) – Please choose one

The best state assignment tends to ___________.

► Maximizes the number of state variables that don’t change in a group of related

states

Minimizes the number of state variables that don’t change in a group of

related states

► Minimize the equivalent states

► None of given options

Question No: 16 ( Marks: 1 ) – Please choose one

The output of this circuit is always ________.

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1

► 0

► A

Question No: 17 ( Marks: 1 ) – Please choose one

A 8-bit serial in / parallel out shift register contains the value “8”, _____ clock signal(s)

will be required to shift the value completely out of the register.

► 1

► 2

► 4

8

Question No: 18 ( Marks: 1 ) – Please choose one

5-bit Johnson counter sequences through ____ states

► 7

► 10

► 32

25

Question No: 19 ( Marks: 1 ) – Please choose one

Assume that a 4-bit serial in/serial out shift register is initially clear. We wish to store the

nibble 1100. What will be the 4-bit pattern after the second clock pulse? (Right-most bit

first.)

► 1100

► 0011

0000

► 1111

Question No: 20 ( Marks: 1 ) – Please choose one

The address from which the data is read, is provided by _______

.

Depends on circuitry

None of given options

RAM

Microprocessor

Question No: 21 ( Marks: 1 ) – Please choose one

FIFO is an acronym for __________

First In, First Out

► Fly in, Fly Out

► Fast in, Fast Out

► None of given options

Question No: 22 ( Marks: 1 ) – Please choose one

LUT is acronym for _________

Look Up Table

► Local User Terminal

► Least Upper Time Period

► None of given options

Question No: 23 ( Marks: 1 ) – Please choose one

The voltage gain of the Inverting Amplifier is given by the relation ________

Vout / Vin = – Rf / Ri

► Vout / Rf = – Vin / Ri

► Rf / Vin = – Ri / Vout

► Rf / Vin = Ri / Vout

Question No: 24 ( Marks: 1 ) – Please choose one

______ of a D/A converter is determined by comparing the actual output of a D/A

converter with the expected output.

► Resolution

Accuracy

► Quantization

► Missing Code

Question No: 25 ( Marks: 1 ) – Please choose one

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Above is the circuit diagram of _______.

► Asynchronous up-counter

► Asynchronous down-counter

Synchronous up-counter

► Synchronous down-counter

Question No: 26 ( Marks: 1 ) – Please choose one

The sequence of states that are implemented by a n-bit Johnson counter is

► n+2 (n plus 2)

2n (n multiplied by 2)

► 2n (2 raise to power n)

► n2 (n raise to power 2)

Question No: 27 ( Marks: 2 )

Draw the Truth-Table of NOR based S-R Latch

input output

S R QT +1

0 0 QT

0 1 0

1 0 1

1 1 INVALID

Question No: 28 ( Marks: 2 )

Two state assignments are given in the table below. Identify which state assignment

is best and why?

States State assignment 1 State assignment 2

A 00 00

B 01 01

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C 11 10

D 10 11

Ans:

State assignment 2 is best assignment… it Minimizes the number of state variables that don’t

change in a group of related states

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Question No: 29 ( Marks: 2 )

Write down at least two functions of a register.

Ans:

1. Registers are operating as a coherent unit to hold and generate data.

2. registers functions also include configuration and start-up of certain features,

especially during initialization, buffer storage e.g. video memory for graphics

cards, input/output (I/O) of different kinds,

Question No: 30 ( Marks: 2 )

Define quantization process.

Ans:

The process by which we can convert an analogue signal into digital signal (code) is known as

quantization process.

Question No: 31 ( Marks: 3 )

How can we calculate the frequency of an unknown signal?

Ans:

The frequency of a particular event is accomplished by counting the number of times that

event occurs within a specific time interval, then dividing the count by the length of the

time interval.

Question No: 32 ( Marks: 3 )

Given the following statement used in PLD programming:

Y PIN 23 ISTYPE ‘com’;

Explain what does this statement mean?

Ans:

The Y variable is a ‘Combinational’ output available directly from the AND-OR gate array

output. The active-low or active-high output of the Registered Mode can also be

specified in the declaration statement

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Question No: 33 ( Marks: 3 )

Explain dynamic RAM in your own words.

Ans:

Dram use latch to store a single bit of information.the main drawback of it id the

discharge of capacitor over a period of time.here four gates are used in making a

singlelatch. In terms of transistors, 4 to 6 transistors are required to implement a single

storage cell. In order to build memories with higher densities, a single transistor is used

to store a binary value. A single transistor can not store a binary value however it is used

to charge and discharge a capacitor. The capacitor can not retain the charge, therefore it

has to be periodically charged

through a refresh cycle.

Question No: 34 ( Marks: 5 )

You are given the Next-state table of a moor machine, using this information draw

the state diagram of the machine.

Present State Next State

Q2 Q1 Q0 Q2 Q1 Q0

0 1 1 1 1 1

1 1 1 0 0 1

0 0 1 0 1 0

0 1 0 1 0 0

1 0 0 1 1 0

1 1 0 0 1 1

Question No: 35 ( Marks: 5 )

Explain Memory Select or Enable Signals

Memory Select or Enable Signal:

There are more than one memory chips to store program

Information in daily use computers. read or write operation is carried out on a single

The unique location is accessed in one of the several memory chips, so single memory

chips is selected before a read or write operation can be carried out. All memory chips

have a chip enable or chip select signal which has to be activated before the memory

can be accessed.

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Question No: 36 ( Marks: 5 )

Performance characteristics of D/A converters are determined by five parameters.

Name them.

Ans:

Performances characteristics of D/A converters are determined by five parameters

are as follow:

1. Accuracy

2. Setting time

3. Monotonicity

4. Linearity

5. Resolution