320+ Digital Principles and System Design Solved MCQs

1.

Any signed negative binary number is recognised by its                  

A. msb
B. lsb
C. byte
D. nibble
Answer» A. msb
Explanation: any negative number is recognized by its msb (most significant bit).
2.

The parameter through which 16 distinct values can be represented is known as                  

A. bit
B. byte
C. word
D. nibble
Answer» C. word
Explanation: it can be represented up to 16 different values with the help of a word. nibble is a combination of four bits and byte is a combination of 8 bits. it is “word” which is said to be a collection of 16-bits on most of the systems.
3.

If the decimal number is a fraction then its binary equivalent is obtained by                  the number continuously by 2.

A. dividing
B. multiplying
C. adding
D. subtracting
Answer» B. multiplying
Explanation: on multiplying the decimal number continuously by 2, the binary equivalent is obtained by the collection of the integer part. however, if it’s an integer, then it’s binary equivalent is determined by dividing the number by 2 and collecting the remainders.
4.

The representation of octal number (532.2)8 in decimal is                  

A. (346.25)10
B. (532.864)10
C. (340.67)10
D. (531.668)10
Answer» A. (346.25)10
Explanation: octal to decimal conversion is obtained by multiplying 8 to the power of base index along with the value at that index position.
5.

The decimal equivalent of the binary number (1011.011)2 is                  

A. (11.375)10
B. (10.123)10
C. (11.175)10
D. (9.23)10
Answer» A. (11.375)10
Explanation: binary to decimal conversion is obtained by multiplying 2 to the power of base index along with the value at that index position.
6.

An important drawback of binary system is

A. it requires very large string of 1’s and 0’s to represent a decimal number
B. it requires sparingly small string of 1’s and 0’s to represent a decimal number
C. it requires large string of 1’s and small string of 0’s to represent a decimal number
D. it requires small string of 1’s and large string of 0’s to represent a decimal number
Answer» A. it requires very large string of 1’s and 0’s to represent a decimal number
Explanation: the most vital drawback of binary system is that it requires very large string of 1’s and 0’s
7.

The decimal equivalent of the octal number (645)8 is              

A. (450)10
B. (451)10
C. (421)10
D. (501)10
Answer» C. (421)10
Explanation: octal to decimal conversion is obtained by multiplying 8 to the power of base index along with the value at that index position.
8.

The largest two digit hexadecimal number is

A. (fe)16
B. (fd)16
C. (ff)16
D. (ef)16
Answer» C. (ff)16
Explanation: (fe)16 is 254 in decimal system, while (fd)16 is 253. (ef)16 is 239 in decimal system. and,
9.

What is the addition of the binary numbers 11011011010 and 010100101?

A. 0111001000
B. 1100110110
C. 11101111111
D. 10011010011
Answer» C. 11101111111
Explanation: the rules for binary addition are : 0 + 0 = 0
10.

Representation of hexadecimal number (6DE)H in decimal:

A. 6 * 162 + 13 * 161 + 14 * 160
B. 6 * 162 + 12 * 161 + 13 * 160
C. 6 * 162 + 11 * 161 + 14 * 160
D. 6 * 162 + 14 * 161 + 15 * 160
Answer» A. 6 * 162 + 13 * 161 + 14 * 160
Explanation: hexadecimal to decimal conversion is obtained by multiplying 16 to the power of base index along with the value at that index position.
11.

100101 × 0110 = ?

A. 1011001111
B. 0100110011
C. 101111110
D. 0110100101
Answer» C. 101111110
Explanation: the rules for binary multiplication are: 0 * 0 = 0
12.

Perform multiplication of the binary numbers: 01001 × 01011 = ?

A. 001100011
B. 110011100
C. 010100110
D. 101010111
Answer» A. 001100011
Explanation: the rules for binary multiplication are: 0 * 0 = 0
13.

Divide the binary numbers: 111101 ÷ 1001 and find the remainder

A. 0010
B. 1010
C. 1100
D. 0011
Answer» D. 0011
Explanation: binary division is accomplished using long division method.
14.

Divide the binary number (011010000) by (0101) and find the quotient

A. 100011
B. 101001
C. 110010
D. 010001
Answer» B. 101001
15.

Binary coded decimal is a combination of

A. two binary digits
B. three binary digits
C. four binary digits
D. five binary digits
Answer» C. four binary digits
Explanation: binary coded decimal is a combination of 4 binary digits. for example-8421.
16.

The decimal number 10 is represented in its BCD form as                      

A. 10100000
B. 01010111
C. 00010000
D. 00101011
Answer» C. 00010000
Explanation: the decimal number 10 is represented in its bcd form as 0001 0000, in accordance to 8421 for each of the two digits.
17.

Carry out BCD subtraction for (68) – (61) using 10’s complement method.

A. 00000111
B. 01110000
C. 100000111
D. 011111000
Answer» A. 00000111
Explanation: first the two numbers are converted into their respective bcd form using 8421 sequence. then binary subtraction is carried out.
18.

When numbers, letters or words are represented by a special group of symbols, this process is called

A. decoding
B. encoding
C. digitizing
D. inverting
Answer» B. encoding
Explanation: when numbers, letters or words are represented by a special group of symbols, this process is called encoding. encoding in the sense of fetching the codes or words in a computer. it is done to secure the transmission of information.
19.

A three digit decimal number requires                  for representation in the conventional BCD format.

A. 3 bits
B. 6 bits
C. 12 bits
D. 24 bits
Answer» C. 12 bits
Explanation: the number of bits needed to represent a given decimal number is always greater than the number of bits required for a straight binary encoding of the same. hence, a three digit decimal number requires 12 bits for representation in bcd format.
20.

How many bits would be required to encode decimal numbers 0 to 9999 in straight binary codes?

A. 12
B. 14
C. 16
D. 18
Answer» B. 14
Explanation: total number of decimals to be represented = 10000 = 104 = 2n (where n is the number of bits required) = 213.29. therefore, the number of bits required for straight binary encoding = 14.
21.

The excess-3 code for 597 is given by                      

A. 100011001010
B. 100010100111
C. 010110010111
D. 010110101101
Answer» A. 100011001010
Explanation: the addition of ‘3’ to each digit yields the three new digits ‘8’, ’12’ and ’10’. hence, the corresponding four-bit binary equivalents are 100011001010, in accordance to 8421 format.
22.

The decimal equivalent of the excess-3 number 110010100011.01110101 is                            

A. 970.42
B. 1253.75
C. 861.75
D. 1132.87
Answer» A. 970.42
Explanation: the conversion of binary numbers into digits ‘1100’, ‘1010’, ‘0011’, ‘0111’ and ‘0101’ gives
23.

In boolean algebra, the OR operation is performed by which properties?

A. associative properties
B. commutative properties
C. distributive properties
D. all of the mentioned
Answer» D. all of the mentioned
Explanation: the expression for associative property is given by a+(b+c) = (a+b)+c & a*(b*c) = (a*b)*c.
24.

The expression for Absorption law is given by

A. a + ab = a
B. a + ab = b
C. ab + aa’ = a
D. a + b = b + a
Answer» A. a + ab = a
Explanation: the expression for absorption law is given by: a+ab = a.
25.

DeMorgan’s theorem states that                    

A. (ab)’ = a’ + b’
B. (a + b)’ = a’ * b
C. a’ + b’ = a’b’
D. (ab)’ = a’ + b
Answer» A. (ab)’ = a’ + b’
Explanation: the demorgan’s law states that (ab)’ = a’ + b’ & (a + b)’ = a’ * b’, as per the dual property.
26.

(A + B)(A’ * B’) = ?

A. 1
B. 0
C. ab
D. ab’
Answer» B. 0
Explanation: the demorgan’s law states that (ab)’ = a’ + b’ & (a + b)’ = a’ * b’, as per the dual property.
27.

According to boolean law: A + 1 = ?                    

A. 1
B. a
C. 0
D. a’
Answer» A. 1
Explanation: a + 1 = 1, as per 1’s property.
28.

The involution of A is equal to                    

A. a
B. a’
C. 1
D. 0
Answer» A. a
Explanation: the involution of a means double inversion of a (i.e. a”) and is equal to a.
29.

Simplify Y = AB’ + (A’ + B)C.

A. ab’ + c
B. ab + ac
C. a’b + ac’
D. ab + a
Answer» A. ab’ + c
Explanation: y = ab’ + (a’ + b)c = ab’ + (ab’)’c
30.

The boolean function A + BC is a reduced form of

A. ab + bc
B. (a + b)(a + c)
C. a’b + ab’c
D. (a + c)b
Answer» B. (a + b)(a + c)
Explanation: (a + b)(a + c) = aa + ac + ab + bc
31.

In which of the following gates the output is 1 if and only if at least one input is 1?

A. and
B. nor
C. nand
D. or
Answer» D. or
Explanation: in or gate we need at least one bit to be equal to 1 to generate the output as 1 because or means any of the condition out of two is equal to 1 which means if at least one input is 1 then it shows output as 1.
32.

The time required for a gate or inverter to change its state is called                      

A. rise time
B. decay time
C. propagation time
D. charging time
Answer» C. propagation time
Explanation: the time required for a gate or inverter to change its state is called propagation time.
33.

What is the minimum number of two input NAND gates used to perform the function of two input OR gates?

A. one
B. two
C. three
D. four
Answer» C. three
Explanation: y = a + b. this is the equation of or gate. we require 3 nand gates to create or gate. we can also write,
34.

Odd parity of word can be conveniently tested by

A. or gate
B. and gate
C. nand gate
D. xor gate
Answer» D. xor gate
Explanation: odd parity of word can be conveniently tested by xor gate, since, xor outputs 1 only when the input has odd number of 1’s.
35.

The number of full and half adders are required to add 16-bit number is                      

A. 8 half adders, 8 full adders
B. 1 half adders, 15 full adders
C. 16 half adders, 0 full adders
D. 4 half adders, 12 full adders
Answer» B. 1 half adders, 15 full adders
Explanation: half adder has two inputs and two outputs whereas full adder has 3 inputs and 2 outputs. one half adder can add the least significant bit of the two numbers whereas full adders are required to add the remaining 15 bits as they all involve adding carries.
36.

Which of the following will give the sum of full adders as output?

A. three point major circuit
B. three bit parity checker
C. three bit comparator
D. three bit counter
Answer» D. three bit counter
Explanation: counters are used for counting purposes in ascending or descending order. three bit counter will give the sum of full adders as output.
37.

An OR gate can be imagined as                          

A. switches connected in series
B. switches connected in parallel
C. mos transistor connected in series
D. bjt transistor connected in series
Answer» B. switches connected in parallel
Explanation: or gate means addition of two inputs, which outputs when any of the input is high. due to this reason, it is imagined as switches connected in parallel.
38.

How many full adders are required to construct an m-bit parallel adder?

A. m/2
B. m
C. m-1
D. m+1
Answer» C. m-1
Explanation: we need adder for every bit. so we should need m bit adders. a full adder adds a carry bit to two inputs and produces an output and a carry. but the most significant bits can use a half adder which differs from the full adder as in that it has no carry input, so we need m-1 full adders and 1 half adder in m bit parallel adder.
39.

Boolean Function is of the form of                  

A. truth values
B. k=f(x,y,x)
C. algebraic expression
D. truth table
Answer» A. truth values
Explanation: the boolean function is of the form of algebraic expressions or truth table. a boolean function is of the form as that of option 2. the result obtained from a boolean function can be a truth value or a fallacy.
40.

The result of X+X.Y is X.

A. true
B. false
Answer» A. true
Explanation: this is a boolean expression. it can be evaluated as :
41.

In the boolean function w=f(X,Y,Z), what is the RHS referred to as                  

A. right hand side
B. expression
C. literals
D. boolean
Answer» B. expression
Explanation: the rhs is commonly referred to as the expression. the symbols x, y and z are commonly referred to as the literals of the function.
42.

The general form for calculating the number of rows in a truth table is                  

A. 2n
B. 2n+1
C. 2n
D. 2n+1
Answer» C. 2n
Explanation: the general form for the calculation of rows in a truth table is 2n . here, n= number of literals in the function.
43.

The number of literals in the expression F=X.Y’ + Z are                            

A. 4
B. 3
C. 2
D. 1
Answer» B. 3
Explanation: literals the generally the number of variables used in any boolean expression. here, since there are 3 variables x, y and z, therefore the answer is 3.
44.

The complement term for X’.Y’.Z + X.Y will be

A. xyz’+x’y’
B. (x+y+z’)(x’+y’)
C. (x+y+z’)(x’+y)
D. (x+y+z’)(x’+y)
Answer» B. (x+y+z’)(x’+y’)
Explanation: the or and and operators are interchanged. the complement terms are reduced to normal terms and the result is obtained.
45.

What is the complement of X’Y’Z?

A. x+yz
B. x’+y+’z’
C. x+y+z’
D. xyz’
Answer» C. x+y+z’
Explanation: the complement is obtained by converting the complement terms to normal terms and vice versa. also, the or and and operators are
46.

The minterm of any expression is denoted by

A. mt
B. m
C. m
D. min
Answer» B. m
Explanation: the variables forming an and term is generally the minterm. it is denoted by m. (lower case letter).
47.

The min term when X=Y=Z=0 is                            

A. x’+y’+z’
B. xyz
C. x’y’z’
D. x+y+z
Answer» C. x’y’z’
Explanation: there minterm expression is obtained using the and term. here, when x=y=z=0, the expression obtained is x’y’z’.
48.

The max term when X=Y=Z=1 is                  

A. x’+y’+z’
B. xyz
C. x’y’z’
D. x+y+z
Answer» A. x’+y’+z’
Explanation: the max term consists of variables forming an or term. here, when x=y=z=1, the expression is x’+y’+z’.
49.

A product term containing all K variables of the function in either complemented or uncomplemented form is called a                      

A. minterm
B. maxterm
C. midterm
D. ∑ term
Answer» A. minterm
Explanation: a product term containing all k variables of the function in either complemented or uncomplemented form is called a minterm. a sum term containing all k variables of the function in either complemented or uncomplemented form is called a maxterm.
50.

The canonical sum of product form of the function y(A,B) = A + B is                      

A. ab + bb + a’a
B. ab + ab’ + a’b
C. ba + ba’ + a’b’
D. ab’ + a’b + a’b’
Answer» B. ab + ab’ + a’b
Explanation: a + b = a.1 + b.1 = a(b + b’) + b(a + a’) = ab + ab’ + ba +ba’ = ab + ab’ + a’b = ab
51.

A variable on its own or in its complemented form is known as a                      

A. product term
B. literal
C. sum term
D. word
Answer» B. literal
Explanation: a literal is a single logic variable or its complement. for example — x, y, a’, z, x’ etc.
52.

Maxterm is the sum of                      of the corresponding Minterm with its literal complemented.

A. terms
B. words
C. numbers
D. nibble
Answer» A. terms
Explanation: maxterm is the sum of terms of the corresponding minterm with its literal complemented.
53.

Canonical form is a unique way of representing

A. sop
B. minterm
C. boolean expressions
D. pos
Answer» C. boolean expressions
Explanation: boolean expressions are represented through canonical form. an example of canonical form is a’b’c’ + ab’c + abc’.
54.

There are                            Minterms for 3 variables (a, b, c).

A. 0
B. 2
C. 8
D. 1
Answer» C. 8
Explanation: minterm is given by 2n. so, 23 = 8 minterms are required.
55.

                           expressions can be implemented using either (1) 2-level AND-OR logic circuits or (2) 2-level NAND logic circuits.

A. pos
B. literals
C. sop
D. pos
Answer» C. sop
Explanation: sop expressions can be implemented using either (1) 2-level and-or logic circuits or (2) 2-level nand logic circuits.
56.

There are              cells in a 4-variable K-map.

A. 12
B. 16
C. 18
D. 8
Answer» B. 16
Explanation: there are 16 = (24) cells in a 4-variable k-map.
57.

The K-map based Boolean reduction is based on the following Unifying Theorem: A + A’ = 1.

A. impact
B. non impact
C. force
D. complementarity
Answer» B. non impact
Explanation: the given expression a +a’ = 1 is based on non-impact unifying theorem.
58.

Each product term of a group, w’.x.y’ and w.y, represents the                         in that group.

A. input
B. pos
C. sum-of-minterms
D. sum of maxterms
Answer» C. sum-of-minterms
Explanation: in a minterm, each variable w, x or y appears once either as the variable itself or as the inverse. so, the given expression satisfies the property of sum of minterm.
59.

The prime implicant which has at least one element that is not present in any other implicant is known as

A. essential prime implicant
B. implicant
C. complement
D. prime complement
Answer» A. essential prime implicant
Explanation: essential prime implicants are prime implicants that cover an output of the function that no combination of other prime implicants is able to cover.
60.

Product-of-Sums expressions can be implemented using                        

A. 2-level or-and logic circuits
B. 2-level nor logic circuits
C. 2-level xor logic circuits
D. both 2-level or-and and nor logic circuits
Answer» D. both 2-level or-and and nor logic circuits
Explanation: product-of-sums expressions can be implemented using 2-level or-and & nor logic circuits.
61.

Each group of adjacent Minterms (group size in powers of twos) corresponds to a possible product term of the given                        

A. function
B. value
C. set
D. word
Answer» A. function
Explanation: each group of adjacent minterms (group size in powers of twos) corresponds to a possible product term of the given function.
62.

Don’t care conditions can be used for simplifying Boolean expressions in                        

A. registers
B. terms
C. k-maps
D. latches
Answer» C. k-maps
Explanation: don’t care conditions can be used for simplifying boolean expressions in k-maps which helps in pairing with 1/0.
63.

It should be kept in mind that don’t care terms should be used along with the terms that are present in

A. minterms
B. expressions
C. k-map
D. latches
Answer» A. minterms
Explanation: it should be kept in mind that don’t care terms should be used along with the terms that are present in minterms as well as maxterms which reduces the complexity of the boolean expression.
64.

Using the transformation method you can realize any POS realization of OR-AND with only.

A. xor
B. nand
C. and
D. nor
Answer» D. nor
Explanation: using the transformation method we can realize any pos realization of or-and with only nor.
65.

There are many situations in logic design in which simplification of logic expression is possible in terms of XOR and                                    operations.

A. x-nor
B. xor
C. nor
D. nand
Answer» A. x-nor
Explanation: there are many situations in logic design in which simplification of logic expression is possible in terms of xor and xnor operations.
66.

In case of XOR/XNOR simplification we have to look for the following                                

A. diagonal adjacencies
B. offset adjacencies
C. straight adjacencies
D. both diagonal and offset adjencies
Answer» D. both diagonal and offset adjencies
Explanation: in case of xor/xnor simplification we have to look for the following diagonal and offset adjacencies. xor gives output 1 when odd number of 1s are present in input while xnor gives output 1 when even number of 1s or all 0s are present in input.
67.

Entries known as                                mapping.

A. diagonal
B. straight
C. k
D. boolean
Answer» A. diagonal
Explanation: entries known as diagonal mapping. the diagonal mapping holds true when for any relation, there is a projection of product on the factor.
68.

The code where all successive numbers differ from their preceding number by single bit is                      

A. alphanumeric code
B. bcd
C. excess 3
D. gray
Answer» D. gray
Explanation: the code where all successive numbers differ from their preceding number by single bit is gray code. it is an unweighted code. the most important characteristic of this code is that only a single bit change occurs when going from one code number to next. bcd code is one in which decimal digits are represented by a group of 4-bits each, whereas, in excess-3 code, the decimal numbers are incremented by 3 and then written in their bcd format.
69.

How many AND gates are required to realize Y = CD + EF + G?

A. 4
B. 5
C. 3
D. 2
Answer» D. 2
Explanation: to realize y = cd + ef + g, two and gates are required and two or gates are required.
70.

The NOR gate output will be high if the two inputs are                      

A. 00
B. 01
C. 10
D. 11
Answer» A. 00
Explanation: in 01, 10 or 11 output is low if any of the i/p is high. so, the correct option will be 00.
71.

A full adder logic circuit will have                      

A. two inputs and one output
B. three inputs and three outputs
C. two inputs and two outputs
D. three inputs and two outputs
Answer» D. three inputs and two outputs
Explanation: a full adder circuit will add two bits and it will also accounts the carry input generated in the previous stage. thus three inputs and two outputs (sum and carry) are there. in case of half adder circuit, there are only two inputs bits and two outputs (sum and carry).
72.

How many two input AND gates and two input OR gates are required to realize Y = BD + CE + AB?

A. 3, 2
B. 4, 2
C. 1, 1
D. 2, 3
Answer» A. 3, 2
Explanation: there are three product terms. so, three and gates of two inputs are required. as only two input or gates are available, so two or gates are required to get the logical sum of three product terms.
73.

Which of following are known as universal gates?

A. nand & nor
B. and & or
C. xor & or
D. ex-nor & xor
Answer» A. nand & nor
Explanation: the nand & nor gates are known as universal gates because any digital circuit can be realized completely by using either of these two gates, and also they can generate the 3 basic gates and, or and not.
74.

Which of the circuits in figure (a to d) is the sum-of- products implementation of figure (e)?

A. x=ab’+a’b
B. x=(ab)’+ab
C. x=(ab)’+a’b’
D. x=a’b’+ab
Answer» D. x=a’b’+ab
Explanation: 1st output of and gate is = a’b’ 2nd and gate’s output is = ab and,
75.

The device shown here is most likely a                  

A. a
B. b
C. c
D. d
Answer» D. d
Explanation: sop means sum of products form which represents the sum of product terms having variables in complemented as well as in uncomplemented form. here, the diagram of d contains the or gate followed by the and gates, so it is in sop form.
76.

What type of logic circuit is represented by the figure shown below?

A. xor
B. xnor
C. and
D. xand
Answer» B. xnor
Explanation: after solving the circuit we get (a’b’)+ab as output, which is xnor operation. thus, it will produce 1 when inputs are even number of 1s or all 0s, and produce 0 when input is odd number of 1s.
77.

What is the indication of a short to ground in the output of a driving gate?

A. only the output of the defective gate is affected
B. there is a signal loss to all load gates
C. the node may be stuck in either the high or the low state
D. the affected node will be stuck in the high state
Answer» B. there is a signal loss to all load gates
Explanation: short to ground in the output of a driving gate indicates of a signal loss to all load gates. this results in information being disrupted and loss of data.
78.

For the device shown here, assume the D input is LOW, both S inputs are LOW and the input is LOW. What is the status of the Y’ outputs?

A. d
B. a
C. c
D. b
Answer» A. d
Explanation: when both inputs are same then the o/p is high for a xnor gate.
79.

Which of the following combinations of logic gates can decode binary 1101?

A. one 4-input and gate
B. one 4-input and gate, one inverter
C. one 4-input and gate, one or gate
D. one 4-input nand gate, one inverter
Answer» B. one 4-input and gate, one inverter
Explanation: for decoding any number output must be high for that code and this is possible in one 4-
80.

The carry propagation can be expressed as

A. cp = ab
B. cp = a + b
C. all but y0 are low
D. all but y0 are high
Answer» B. cp = a + b
Explanation: this happens in parallel adders (where we try to add numbers in parallel via more than one
81.

3 bits full adder contains                  

A. 3 combinational inputs
B. 4 combinational inputs
C. 6 combinational inputs
D. 8 combinational inputs
Answer» D. 8 combinational inputs
Explanation: full adder is a combinational circuit with 3 input bits and 2 output bits carry and sum. three bits full adder requires 23 = 8 combinational circuits.
82.

The basic building blocks of the arithmetic unit in a digital computers are                          

A. subtractors
B. adders
C. multiplexer
D. comparator
Answer» B. adders
Explanation: the basic building blocks of the arithmetic unit in a digital computers are adders. since, a parallel adder is constructed with a number of full- adder circuits connected in cascade. by controlling the data inputs to the parallel adder, it is possible to obtain different types of arithmetic operations.
83.

A digital system consists of            types of circuits.

A. 2
B. 3
C. 4
D. 5
Answer» A. 2
Explanation: a digital system consists of two types of circuits and these are combinational and sequential logic circuit. combinational circuits are the ones
84.

In a sequential circuit, the output at any time depends only on the input values at that time.

A. past output values
B. intermediate values
C. both past output and present input
D. present input values
Answer» C. both past output and present input
Explanation: in a sequential circuit, the output at any time depends on the present input values as well as past output values. it also depends on clock pulses depending whether it’s synchronous or asynchronous sequential circuits.
85.

The design of an ALU is based on                          

A. sequential logic
B. combinational logic
C. multiplexing
D. de-multiplexing
Answer» B. combinational logic
Explanation: the design of an alu is based on combinational logic. because the unit has a regular pattern, it can be broken into identical stages connected in cascade through carries.
86.

If the two numbers are unsigned, the bit conditions of interest are the              carry and a possible             result.

A. input, zero
B. output, one
C. input, one
D. output, zero
Answer» D. output, zero
Explanation: if the two numbers are unsigned, the bit conditions of interest are the output carry and a possible zero result.
87.

If the two numbers include a sign bit in the highest order position, the bit conditions of interest are the sign of the result, a zero indication and                        

A. an underflow condition
B. a neutral condition
C. an overflow condition
D. one indication
Answer» C. an overflow condition
Explanation: if the two numbers include a sign bit in the highest order position, the bit conditions of interest are the sign of the result, a zero indication and an overflow condition.
88.

In parts of the processor, adders are used to calculate

A. addresses
B. table indices
C. increment and decrement operators
D. all of the mentioned
Answer» D. all of the mentioned
Explanation: adders are used to perform the operation of addition. thus, in parts of the processor, adders are used to calculate addresses, table indices, increment and decrement operators, and similar operations.
89.

Total number of inputs in a half adder is

A. 2
B. 3
C. 4
D. 1
Answer» A. 2
Explanation: total number of inputs in a half adder is two. since, an exor gates has 2 inputs and carry is connected with the input of exor gates. the output of half-adder is also 2, them being, sum and carry. the output of exor gives sum and that of and gives carry.
90.

In which operation carry is obtained?

A. subtraction
B. addition
C. multiplication
D. both addition and subtraction
Answer» B. addition
Explanation: in addition, carry is obtained. for example: 1 0 1 + 1 1 1 = 1 0 0; in this example carry is
91.

If A and B are the inputs of a half adder, the carry is given by                      

A. a and b
B. a or b
C. a xor b
D. a ex-nor b
Answer» A. a and b
Explanation: if a and b are the inputs of a half adder, the carry is given by: a(and)b, while the sum is given by a xor b.
92.

Half-adders have a major limitation in that they cannot                      

A. accept a carry bit from a present stage
B. accept a carry bit from a next stage
C. accept a carry bit from a previous stage
D. accept a carry bit from the following stages
Answer» C. accept a carry bit from a previous stage
Explanation: half-adders have a major limitation in that they cannot accept a carry bit from a previous stage, meaning that they cannot be chained together to add multi-bit numbers. however, the two output bits of a half-adder can also represent the result a+b=3 as sum and carry both being high.
93.

If A, B and C are the inputs of a full adder then the carry is given by                      

A. a and b or (a or b) and c
B. a or b or (a and b) c
C. (a and b) or (a and b)c
D. a xor b xor (a xor b) and c
Answer» A. a and b or (a or b) and c
Explanation: if a, b and c are the inputs of a full adder then the carry is given by a and b or (a or
94.

How many AND, OR and EXOR gates are required for the configuration of full adder?

A. 1, 2, 2
B. 2, 1, 2
C. 3, 1, 2
D. 4, 0, 1
Answer» B. 2, 1, 2
Explanation: there are 2 and, 1 or and 2 exor gates required for the configuration of full adder, provided using half adder. otherwise, configuration of full adder would require 3 and, 2 or and 2 exor.
95.

How many outputs are required for the implementation of a subtractor?

A. 1
B. 2
C. 3
D. 4
Answer» B. 2
Explanation: there are two outputs required for the
96.

Let the input of a subtractor is A and B then what the output will be if A = B?

A. 0
B. 1
C. a
D. b
Answer» A. 0
Explanation: the output for a = b will be 0. if a = b, it means that a = b = 0 or a = b = 1. in both of the situation subtractor gives 0 as the output.
97.

Let A and B is the input of a subtractor then the output will be                        

A. a xor b
B. a and b
C. a or b
D. a exnor b
Answer» A. a xor b
Explanation: the subtractor has two outputs borow and difference. since, the difference output of a subtractor is given by ab’ + ba’ and this is the output of a xor gate. so, the final difference output is ab’ + ba’.
98.

Let A and B is the input of a subtractor then the borrow will be                        

A. a and b’
B. a’ and b
C. a or b
D. a and b
Answer» B. a’ and b
Explanation: the borrow of a subtractor is received through and gate whose one input is inverted. on
99.

The full subtractor can be implemented using

A. two xor and an or gates
B. two half subtractors and an or gate
C. two multiplexers and an and gate
D. two comparators and an and gate
Answer» B. two half subtractors and an or gate
Explanation: a full subtractor has 3 input bits and two outputs bits borrow and difference. the full subtractor can be implemented using two half subtractors and an or gate.
100.

The output of a subtractor is given by (if A, B and X are the inputs).

A. a and b xor x
B. a xor b xor x
C. a or b nor x
D. a nor b xor x
Answer» B. a xor b xor x
Explanation: the difference output of a subtractor is given by (if a, b and x are the inputs) a xor b xor x.
Tags
Question and answers in Digital Principles and System Design, Digital Principles and System Design multiple choice questions and answers, Digital Principles and System Design Important MCQs, Solved MCQs for Digital Principles and System Design, Digital Principles and System Design MCQs with answers PDF download