Digital Fundamentals and Computer Organization - Question Bank
Unit – I
: INTRODUCTION TO DIGITAL DESIGN
1.Define the term
digital.
The term digital
refers to any process that is accomplished using discrete units
2.What is meant
by bit?
A binary digit is
called bit
3.What is the
best example of digital system?
Digital computer
is the best example of a digital system.
4.Define byte?
A group of 8
bits.
5.List the number
systems?
i) Decimal
Number system
ii) Binary
Number system
iii) Octal
Number system
iv) Hexadecimal
Number system
6.State the sequence
of operator precedence in Boolean expression?
i) Parenthesis
ii) AND
iii) OR
7.What is the
abbreviation of ASCII and EBCDIC code?
ASCII- American
Standard Code for Information Interchange.
EBCDIC- Extended Binary Coded
Decimal Information Code.
8.What are the
universal gates?
NAND and NOR
9.What are the
different types of number complements?
i) r’s
Complement
ii) (r-1)’s
Complement.
10.Why
complementing a number representation is needed?
Complementing a number becomes as
in digital computer for simplifying the subtraction operation and for logical manipulation complements are used.
11.How to
represent a positive and negative sign in computers?
Positive (+) sign
by 0
Negative (-) sign
by 1.
12.What is meant
by Map method?
The map method provides a simple straightforward procedure for minimizing
Boolean function.
13.What is meant
by two variable map?
Two variable map have four minterms for two variables, hence the map
consists of four squares, one for
each minterm
14.What is meant
by three variable map?
Three variable map
have 8 minterms for three variables, hence the map consists of
8 squares, one
for each minterm
15.Which gate is
equal to AND-inverter Gate?
NAND gate.
16.Which gate is
equal to OR-inverter Gate?
NOR gate.
17.Bubbled OR
gate is equal to--------------
NAND gate
18. Bubbled AND
gate is equal to--------------
NOR gate
19.What is the
use of Don’t care conditions?
Any digital circuit using this code operates under the assumption that
these unused combinations will never
occur as long as the system
20.Express the function f(x, y, z)=1 in the sum of minterms and a
product of maxterms?
Minterms=∑(0,1,2,3,4,5,6,7)
Maxterms=Nomaxterms.
21.What is the algebraic function of Exclusive-OR gate and Exclusive-NOR
gate?
F=xy1 + x1y
F=xy +x1y1
22.What are the
methods adopted to reduce Boolean function?
i) Karnaugh map
ii) Tabular method or Quine
mccluskey method
iii) Variable entered map
technique.
23.Why we go in
for tabulation method?
This method can be applied to problems with many variables and has the advantage of being suitable for machine
computation.
24.State the limitations
of karnaugh map.
i) Generally it is limited to six variable map (i.e.)
more then six variable
involving expressions are not reduced.
ii) The map method is restricted in its capability
since they are useful for
simplifying only Boolean expression
represented in standard form.
25.What is
tabulation method?
A method involving an exhaustive tabular search method for the minimum expression to solve a Boolean equation is called
as a tabulation method.
26.What are
prime-implicants?
The terms remained unchecked are called prime-implicants. They cannot be reduced further.
27.Explain or list
out the advantages and disadvantages of
K-map method?
The advantages of
the K-map method are
i.
It is a fast
method for simplifying expression up to four variables.
ii. It gives a visual method of logic simplification.
iii. Prime implicants
and essential prime implicants are identified fast.
iv.
Suitable for both SOP and POS forms of reduction.
v. It
is more suitable
for class room
teachings on logic simplification.
The disadvantages
of the K-map method are
i. It is not suitable for computer reduction.
ii. K-maps are not suitable when
the number of variables involved exceed
four.
iii. Care must be taken to fill
in every cell with the relevant entry, such as a 0, 1 (or) don’t care terms.
28.List out the
advantages and disadvantages of Quine-Mc Cluskey method?
The advantages
are,
a. This is suitable when the number of variables
exceed four.
b. Digital computers can be used to obtain the
solution fast.
c. Essential prime implicants, which are not
evident in K-map, can be clearly
seen in the final results.
The disadvantages
are,
a. Lengthy procedure than K-map.
b. Requires several grouping and steps as
compared to K-map.
c. It is much slower.
d. No visual identification of reduction
process.
UNIT – II: DIGITAL COMPONENTS
29.Define
Positive Logic.
When high voltage or more positive voltage level is associated with
binary ‘1’ and while the low or less
positive level is associated with binary ‘0’ then the system adhering to this is called positive logic.
30.Define
Negative Logic.
When high voltage level is
associated with binary ‘0’ and while the low level is associated with binary ‘1’ then the system adhering to this is called
negative logic
31 .List the
characteristics of digital Ics
i) propagation delay
ii) power dissipation
iii) Fan-in
iv) Fan-out
v) Noise margin
32 .What is
propagation delay?
It is the average transition delay time for the signal to propagate from
input to output when the signals
change in value.
33.What is Noise
margin?
It is the limit of a noise voltage, which may be present with out
impairing the proper operation of
the circuit.
34.What is power
dissipation?
It is the power consumed by the gate, which must be available from the
power
supply.
35.Why parity
checker is needed?
Parity checker is required at the receiver side to check whether the
expected parity is equal to the
calculated parity or not. If they are not equal then it is found that the received data has error.
36.What is meant
by parity bit?
Parity bit is an extra bit included with a binary message to make the
number of 1’s either odd or even. The
message, including the parity bit is transmitted and then checked at the receiving and for errors.
37.Why parity
generator necessary?
Parity generator
is essential to generate parity bit in the transmitter.
38.What is IC?
An integrated circuit is a small silicon semiconductor crystal called a
chip
containing electrical components
such as transistors, diodes, resistors and capacitors. The
various components are interconnected inside the chip to form an electronic
circuit.
39 What are the
needs for binary codes?
a. Code is used to represent letters, numbers and punctuation marks.
b. Coding is required for maximum
efficiency in single transmission.
c. Binary codes are the major components in the synthesis (artificial
generation)
of speech and video signals.
d. By using error detecting codes, errors generated in signal
transmission can be
detected.
e. Codes are used for data
compression by which large amounts of data aretransmitted in
very short duration of time.
40.Mention the
different type of binary codes?
The various types
of binary codes are,
1. BCD code (Binary Coded decimal).
2. Self-complementing code.
3. The excess-3 (X’s-3) code.
Gray code.
4.
Binary
weighted code.
5. Alphanumeric code.
The
ASCII code.
6. Extended binary-coded decimal interchange code
(EBCDIC).
7. Error-detecting and error-correcting code.
8. Hamming code.
41. List the
advantages and disadvantages of BCD code?
The advantages of
BCD code are
1.
Any large
decimal number can be easily converted into corresponding
binary number
2.
A person
needs to remember only the binary equivalents of decimal
number from 0 to 9.
3. Conversion from BCD into decimal is also very
easy.
The disadvantages
of BCD code are
1.
The code is
least efficient. It requires several symbols to represent even
small numbers.
2. Binary addition and subtraction can lead to wrong
answer.
3. Special codes are required for arithmetic
operations.
4. This is not a self-complementing code.
5. Conversion into other coding schemes requires
special methods.
42.What is meant
by self-complementing code?
A self-complementing code is the one in which the members of the number
system complement on themselves. This
requires the following two conditions to be
satisfied.
1.
The complement
of the number should be obtained from that number by
replacing 1s with 0s and 0s with 1s.
2.
The sum of the number and its complement should
be equal to decimal 9.
Example of a self-complementing code is
i. 2-4-2-1
code.
ii. Excess-3 code.
43.Mention the
advantages of ASCII code?
The following are
the advantages of ASCII code
a. There are 27 =128 possible
combinations. Hence, a large number of symbols,
alphabets etc.., can be easily represented.
b. There is a definite order in which the
alphabets, etc.., are assigned to each code
word.
c.
The parity bits can be added for error-detection and correction.
44. Define state
of sequential circuit?
The binary information stored in the memory elements at any given time
defines the “state” of sequential
circuits.
45.What is meant by
race around condition?
In JK flip-flop output is fed back to the input, and therefore changes in
the output results change in the
input. Due to this in the positive half of the clock pulse if J and K
are both high then output toggles continuously. This condition is known as race around condition.
46.What is
bi-directional shift register and unidirectional shift register?
A register capable of shifting both right and left is called
bi-directional shift register. A register capable of shifting only one direction
is called unidirectional shift register.
47.What are the
disadvantages of ASCII code?
The disadvantages
of ASCII code are
a. The length of the code is larger and hence
more bandwidth is required for
transmission.
b.
With more characters and symbols to represent, this is not completely
sufficient.
48.What is the
truth table?
A truth table lists all possible combinations of inputs and the
corresponding
outputs.
49.Define figure
of merit?
Figure of merits is defined as
the product of speed and power. The speed is specified
in terms of propagation delay time
expressed in nano seconds.
Figure of merits=Propagation delay time (ns)*
Power (mw)
It is specified in pico joules (ns*mw=PJ).
50.What are the
two types of logic circuits for digital systems?
Combinational and sequential
51.Define
Combinational circuit.
A combinational circuit consist of logic gates whose outputs at anytime
are
determined directly from the present combination of inputs without
regard to previous
inputs.
52.Define
sequential circuits.
Their outputs are a function of
the inputs and the state of memory elements. The state of memory elements, in turn, is a function of previous inputs.
53.What is a
half-adder?
The combinational circuit that performs the addition of two bits are
called a half-adder.
54.What is a
full-adder?
The combinational circuit that performs the addition of three bits are
called a full-adder.
55.What is
half-subtractor?
The combinational circuit that performs the subtraction of two bits are
called a half-sub tractor.
56.What is a
full-subtractor?
The combinational circuit that
performs the subtraction of three bits are called a full- sub tractor.
57.What is Binary
parallel adder?
A binary parallel adder is a
digital function that produces the arithemetic sum of two binary numbers in parallel.
58.What is BCD
adder?
A BCD adder is a circuit that adds two BCD digits in parallel and
produces a sum digit also in BCD.
59.What is
Magnitude Comparator?
A Magnitude Comparator is a
combinational circuit that compares two numbers, A and B and determines their relative magnitudes.
60.What is
decoder?
A decoder is a combinational circuit that converts binary information
from ‘n’ input lines to a maximum of
2n unique output lines.
61.What is
encoder?
A decoder is a combinational circuit that converts binary information
from 2nInput lines to a
maximum of ‘n’ unique output lines.
62.Define
Multiplexing?
Multiplexing means transmitting a large number of information units over
a smaller number of channels or
lines.
63.What is
Demultiplexer?
A Demultiplexer is a circuit that receives
information on a
single line and transmits this information on one of 2n
possible output lines
64.Give the truth
table for a half adder.
Input Output
X Y Sum ( S ) Carry ( C )
0 0 0 0
0 1 1 0
1 0 1 0
1 1 0 1
65.Give the truth
table for a half Subtractor.
Input Output
X Y Borrow( B ) Diffe ( D )
0 0 0 0
0 1 1 1
1 0 0 1
1 1 0 0
66.What is code
conversion?
If two systems working with different binary codes are to be synchronized
in operation, then we need digital
circuit which converts one system of codes to the other. The process of conversion is referred to as code
conversion.
67.What is code
converter?
It is a circuit that makes the two systems compatible even though each
uses a different binary code. It is a
device that converts binary signals from a source code to its output code. One example is a BCD to Xs3
converter.
68.What do you
mean by analyzing a combinational circuit?
The reverse process for implementing a Boolean expression is called as
analyzing a combinational circuit.
(ie) the available logic diagram is analyzed step by step and finding the Boolean function
69.Give the
applications of Demultiplexer.
i) It finds its application in Data transmission
system with error detection.
ii) One simple application is
binary to Decimal decoder.
70.Mention the
uses of Demultiplexer.
Demultiplexer is used in computers when a same message has to be sent to different receivers. Not only in computers, but
any time information from one source can be fed to several places.
71.Give other
name for Multiplexer and Demultiplexer.
Multiplexer is
other wise called as Data selector.
Demultiplexer is
otherwise called as Data distributor.
72.What is the
function of the enable input in a Multiplexer?
The function of
the enable input in a MUX is to control the operation of the unit.
73.Give the truth
table for a full Subtractor.
Input Output
X Y Z Borrow ( B ) Diffe
( D )
0 0 0 0 0
0 0 1 1 1
0 1 0 1 1
0 1 1 1 0
1 0 0 0 1
1 0 1 0 0
1 1 0 0 0
1 1 1 1 1
74.Give the truth
table for a full adder.
Input Output
X Y Z Sum ( S ) Carry
( C )
0 0 0 0 0
0 0 1 1 0
0 1 0 1 0
0 1 1 0 1
1 0 0 1 0
1 0 1 0 1
1 1 0 0 1
1 1 1 1 1
75.What is
priority encoder?
A priority encoder is an encoder that includes the priority function.
The operation of the priority encoder is such that if two or more inputs
are equal to 1 at the same time, the input
having the highest priority will take precedence.
76.Can a decoder
function as a Demultiplexer?
Yes. A decoder with enable can function as a Demultiplexer if the
enable line E is taken as a data
input line A and B are taken as selection lines.
77.List out the
applications of multiplexer?
The various
applications of multiplexer are
a. Data routing.
b. Logic function
generator.
c. Control
sequencer.
d.
Parallel-to-serial converter.
78.List out the
applications of decoder?
The applications
of decoder are
a. Decoders are
used in counter system.
b. They are used
in analog to digital converter.
c. Decoder
outputs can be used to drive a display system.
79.List out the
applications of comparators?
The following are
the applications of comparator
a. Comparators are used as a part of the address decoding circuitry in computers
to select a
specific input/output device for the
storage of data.
b. They are used to
actuate circuitry to drive the physical variable towards the reference value.
c. They are used
in control applications.
80.What is
digital comparator?
A comparator is a special combinational circuit designed primarily to compare the relative magnitude of two binary
numbers.
81.List the
classifications of sequential circuit.
i) Synchronous sequential circuit.
ii) Asynchronous sequential circuit.
82.what is
Synchronous sequential circuit?
A Synchronous sequential circuit is a system whose behavior can be
defined from the knowledge of its
signal at discrete instants of time.
83.What is
clocked sequential circuits?
Synchronous sequential circuit that use clock pulses in the inputs of
memory elements are called clocked sequential circuit. One advantage as
that they don’t cause instability problems.
84. What is called
latch?
Latch is a simple memory
element, which consists of a pair of logic gates with their inputs and outputs inter connected in a feedback arrangement, which
permits a single bit to be stored.
85.List different
types of flip-flops.
i) SR flip-flop
ii) Clocked RS flip-flop
iii) D flip-flop
iv) T flip-flop
v) JK flip-flop
vi) JK master slave flip-flop
86.What do you
mean by triggering of flip-flop.
The state of a flip-flop is switched by a momentary change in the input
signal.
This momentary change is called a
trigger and the transition it causes is said to trigger the
flip-flop
87.What is an
excitation table?
During the design process we
usually know the transition from present state to
next state and wish to find the flip-flop
input conditions that will cause the required
transition. A table which lists the
required inputs for a given chance of state is called an
excitation table.
88.Give the
excitation table of a JK flip-flop
Q(t) Q(t+1) J K
0 0 0 X
0 1 1 X
1 0 X 1
1 1 X 0
89.Give the excitation
table of a SR flip-flop
Q(t) Q(t+1) S R
0 0 0 X
0 1 1 0
1 0 0 1
1 1 X 0
90.Give the excitation
table of a T flip-flop
Q(t) Q(t+1) T
0 0 0
0 1 1
1 0 1
1 1 0
91.Give the excitation
table of a D flip-flop
Q(t) Q(t+1) T
0 0 0
0 1 1
1 0 0
1 1 1
92.What is a
characteristic table?
A characteristic table defines
the logical property of the flip-flop and completely characteristic its operation.
93.Give the characteristic equation of a SR flip-flop.
Q(t+1)=S+R1Q
94.Give the
characteristic equation of a D flip-flop.
Q(t+1)=D
95.Give the characteristic equation of a JK flip-flop.
Q(t+1)=JQ1+K1Q
96.Give the characteristic equation of a T flip-flop.
Q(t+1)=TQ1+T1Q
97.What is the
difference between truth table and excitation table.
i) An excitation table is a table that lists the required inputs for a given
change of state.
ii) A truth table is a table indicating the output of a
logic circuit for various
input states.
98.What is
counter?
A counter is used to
count pulse and give the output in binary form.
99.What is synchronous
counter?
In a synchronous counter, the clock pulse is applied simultaneously to
all flipflops. The output of the
flip-flops change state at the same instant. The speed of operation is high compared to an asynchronous counter
100.What is
Asynchronous counter?
In a Asynchronous counter, the clock pulse is applied to the first
flip-flops. The
change of state in the output of this flip-flop serves as a clock pulse
to the next flip-flop
and so on. Here all the flip-flops do not change state at the same instant and
hence speed
is less.
101.Name the
different types of counter.
a) Synchronous
counter
b) Asynchronous
counter
i) Up counter
ii) Down counter
iii) Modulo - N counter
iv) Up/Down counter
102 What is up counter?
A counter that increments the output by one binary
number each time a clock pulse is
applied.
103.What is down
counter?
A counter that decrements the output by one binary
number each time a clock pulse is
applied.
104.What is up/down counter?
A counter, which is capable of operating as an up
counter or down counter, depending
on a control lead.
105 What is a
ripple counter?
A ripple counter is nothing but an asynchronous
counter, in which the output of the
flip-flop change state like a ripple in water.
106 .What are the uses of a counter?
i) The digital clock
ii) Auto parking control
iii) Parallel to serial data
conversion.
107.What is meant by modulus of a counter?
By the term modulus of a counter we say it is the
number of states through which a
counter can progress.
108.what is meant
by natural count of a counter?
By the term natural count of a counter we say
that the maximum number of states through
which a counter can progress.
109.A ripple counter is a ------------ sequential counter.
Ans: Synchronous.
110.What is a modulo
counter?
A counter that
counts from 0 to T is called as modulo counter.
111.What is a ring counter?
A counter formed by circulating a ‘bit’ in a
shift register whose serial output has been
connected to its serial input.
112.What is BCD
counter?
A BCD counter
counts in binary coded decimal from 0000 to 1001 and back to 0000. Because of the return to 0000 after a count
of 1001, a BCD counter does not have a regular
pattern as in a straight binary counter.
113. What are the uses of a ring counter?
i) Control section of a digital
system.
ii) Controlling
events, which occur in strict time sequence.
114.What is a register?
Memory
elements capable of storing one binary word. It consists of a group of flip-flops, which store the binary information.
115.What is Johnson
counter?
It is a ring counter in which the inverted output is fed into the input.
It is also know as a twisted ring
counter.
116. What is a
shift register?
In digital circuits, datas are needed to be moved into a register
(shift in) or moved out of a register
(shift out). A group of flip-flops having either or both of these facilities is
called a shift register.
117. What is
serial shifting?
In a shift register, if the data is moved 1 bit at a time in a serial
fashion, then the technique is
called serial shifting.
118. What is
parallel shifting?
In a shift register all the data are moved simultaneously and then the
technique is called parallel
shifting.
119. Write the uses of
a shift register.
i) Temporary
data storage
ii) Bit manipulations.
120. What is a
cycle counter?
A cycle counter is a
counter that outputs a stated number of counts and then stops.
UNIT – III: FUNCTIONAL UNITS
121. What are the functional units of the Computer.
122. State Instruction.
123. Define Bus Structures.
124. Give the use of Buffer Registers.
125. Explain how to represent 1’s Complement number.
126. Define Memory Locations
127. How memory of the computer is calculated.
128. Give the basic operations involved in memory.
129. List the basic instruction types.
130. List the various types of instruction.
131. Define Addressing Mode.
132. How EA is calculated.
133. Give the use of Indexing and Array and define.
134. List the addressing Modes available.
135. Give the use of Assembler directives.
136. Explain carry-look ahead addition.
137. Define Booth Algorithm.
UNIT – IV: PROCESSING UNIT
138.
Draw the block diagram of the single bus organization
inside the processor.
139.
Explain register transfer.
140.
Give the steps involved in fetching a word from memory.
141.
What are the actions to be performed for executing a
instruction.
142.
Define Multiple Bus Organization.
143.
Draw the block diagram of Control unit organization.
144.
Explain the separation of the decoding and encoding
functions.
145.
Give the block diagram of a complete processor.
146.
Define Hardwired Control unit.
147.
Explain basic organization of a micro programmed
control unit.
148.
How micro instructions are executed.
149.
Explain the Microprogram sequencing.
150.
Draw the flowchart for the microprogram for the ADD.
151.
Give the steps involved in micro-instruction
sequencing.
152.
Give a short note on prefetching micro instruction.
UNIT – V: MEMORY AND I/O ORGANISATION
153 . List the
types of ROM.
i) Programmable
ROM (PROM)
ii) Erasable
ROM (EPROM)
iii) Electrically
Erasable ROM (EEROM)
154.What are the
different types of RAM?
The different
types of RAM are
a. NMOS RAM
(Nitride Metal Oxide Semiconductor RAM)
b. CMOS RAM (Complementary Metal Oxide Semiconductor RAM)
c. Schottky TTL
RAM
d. ELL RAM.
155.What are the
types of arrays in RAM?
RAM has two type
of array namely,
a. Linear array
b. Coincident
array
156.Explain SRAM?
Static
RAM(SRAM) consists of
internal latches that
store the binary information. The stored
information remains valid as long as the power is applied to the unit.
SRAM is easier to use and has shorter read and write cycle.
The memory capacity of a static RAM varies from 64 bit to 1 mega bit.
157.Explain DRAM?
The dynamic RAM (DRAM) is an operating mod, which stores the binary information in the form of electric charges on
capacitors.
The capacitors
are provided inside the chip by MOS transistors.
The stored charges on the capacitors tend to discharge with time and the capacitors must be tending to discharge with time
and the capacitors must be periodically
recharged by refreshing the dynamic memory.
DRAM offers reduced power consumption and larger storage capacity in a single memory chip.
158.What are the
advantages of RAM?
The advantages of RAM
are
a. Non-destructive
read out
b. Fast operating
speed
c. Low power
dissipation
d. Compatibility
e. Economy
159 What is meant
by memory decoding?
The memory IC used in a digital system is selected or enabled only for
the range of addresses assigned to
it .
160.What is access and
cycle time?
The access time of the memory is the time to select word and read it. The
cycle time of a memory is a time
required to complete a write operation.
Part – B (All
Five Units)
1.
(i). Express the Boolean function F =A+B’C in sum of minterms
(ii) Express the
Boolean function F=xy+x’z in
production of maxterms.
2.
Simplify the
Boolean function F(A,B,C,D)= ∑(0,6,8,13,14) Together with the don’t care condition d=∑(2,4,10)and then express the
simplified function in sum of minterms.
3.
Implement the
Boolean function F(X,Y,Z)=(1,2,3,4,5,7)with NAND gates
4.
Simplify the Boolean function F(A,B,C,D)
∑(0,2,3,5,7,8,9,10,11,13,15)and find the prime
implicants and essential prime implicants
5.
Design a full
adder with inputs x,y,z and two outputs S and C .
6.
Design a BCD
adder.
7.
Design a
logic circuit that accepts a 4-bit Grey code and converts it into 4-bit binary code
8.
Write short
notes on: BCD adder, Binary multiplier and Magnitude Comparator
9.
Draw the
circuit for 3-to-8-decoder and implement the functions
F1(A,B,C)=II(0,1,3,7)
F2(A,B,C)=II(2,3,7) using 3-to-8-decoder
10.
Draw the
circuits for Decimal to BCD encoder, Octal-to- Binary encoder & Priority
encoder
11.
Implement
full subtractor using demultiplexer.
12.
Draw the
state diagram and characteristic equations of T,D and JK flip flop
13.
Discuss in
detail shift registers
14.
Discuss
about synchronous counters
15.
Write the
procedure for analyzing a clocked sequential circuit with JK flip flop.
16.
Give a note
on the Control Unit.
17.
Explain the
working principle of MicroProgrammed Control.
18.
Perform the
arithmetic operations over the Signed Numbers with details.
19.
Write a short
note fast adder and fast multiplication and Integer division.
20.
Give a brief
explanation on Memory organization.
21.
Discuss in
detail the architecture of Interrupt handling and controller.
22.
List the
advantages of DMA and explain the DMA in detail.
23.
Explain RAM
and ROM and compare.
24.
Give a short
note on the Addressing Modes and Assembly language and its impact in the design
of Computer.
25.
Number
format conversion (Problems).
26.
Illustrate
with block diagram the concept of Accessing I/O devices.
27.
State and
explain the basic operational concepts of processing unit.
28.
Give a brief
note on Virtual memory and compare it with cache memory.
29.
Write Short
note on Registers and Counters.
30.
Give the
full adder and multiplexer and give its relationship.
