# Recent questions and answers in Digital Logic

1
A $3$ line to $8$ line Decoder is used to implement a $3$-variable Boolean function as shown in figure. The simplified form of output $Y$ is. $\bar{X}Y + \bar{Y}Z + XY\bar{Z}$ $\bar{X}Z +\bar{Y}Z + XYZ$ $X\bar{Y} + X\bar{Z} +\bar{X}YZ$ $X\bar{Y} + X\bar{Z} + \bar{X}Y\bar{Z}$
1 vote
2
Consider a full-adder with the following input values : $x=1, y=0$ and $C_i$(carry input)$=0$ $x=0, y=1$ and $C_i =1$ Compute the value of S(sum) and $C_o$ (carry output) for the above input values : $S=1, C_o=0$ and $S=0, C_o=1$ $S=0, C_o=0$ and $S=1, C_o=1$ $S=1, C_o=1$ and $S=0, C_o=0$ $S=0, C_o=1$ and $S=1, C_o=0$
1 vote
3
The smallest integer that can be represented by an $8$-bit number in $2$'s complement form is : $-256$ $-128$ $-127$ $0$
4
A sequential circuit using D flip-flop and logic gates is shown in Figure, where $X$ and $Y$ are the inputs and $Z$ is the output. The circuit is $\text{S-R}$ Flip-flop with inputs $X = R$ and $Y=S$ $\text{S-R}$ Flip-flop with inputs $X = S$ and $Y=R$ $\text{J-K}$ Flip-flop with inputs $X = J$ and $Y=K$ $\text{J-K}$ Flip-flop with inputs $X = K$ and $Y=J$
5
Simplify the Following boolean function by means of the tabulation method. (a) P(A,B,C,D,E,F,G)=$\sum(20,28,52,60)$ (b) P(A,B,C,D,E,F,G)= $\sum(20,28,38,39,52,60,102,103,127)$ (C) P(A,B,C,D,E,F) = $\sum(6,9,13,18,19,25,27,29,41,45,57,61)$
1 vote
6
7
Addition of all gray code to convert decimal(0-9) into gray code is a)129 b) 108 c) 69 d) 53
1 vote
8
Which will be the equation of simplification of the given K-map? $AB' + B'CD' + A'B'C'$ $AB' + A'B'D' + A'B'C'$ $B'D' + AB' + B'C'$ $B'D' + A'B'C' + AB'$
1 vote
9
How many RAM chips of size $(256K \times 1 \text{ bit})$ are required to build $1$M Byte memory? $8$ $10$ $24$ $32$
10
The result of the subtraction $FD​_{16} - ​88_{16​}$ is $75_{16}$ $65_{16}$ $5E_{16}$ $10_{16}$
1 vote
11
12
Which of the following logic expression is incorrect? $1\oplus0=1$ $1\oplus1\oplus0=1$ $1\oplus1\oplus1=1$ $1\oplus1=0$
1 vote
13
In Boolean algebra $1+1+1+1\dots\dots 800$ times ones $=$ ______ . $1$ $0$ $11$ $800$
14
The number $(25)_6$, in base $6$ is equivalent to _________ in binary number system. $11001$ $10001$ $11000$ $10000$
15
In a ripple counter using edge-triggered $JK$ flip-flops, the pulse input is applied to Clock input of all flip-flops $J$ and $K$ input of one flip-flop $J$ and $K$ input of all flip flops Clock input of one flip-flop
16
A $4$ bit ripple counter and a $4$ bit synchronous counter are made using flip-flops having a propagation delay of $10$ ns each. If the worst case delay in the ripple counter and the synchronous counter be $R$ and $S$ respectively, then $R = 10$ ns, $S = 40$ ns $R = 40$ ns, $S = 10$ ns $R = 10$ ns, $S = 30$ ns $R = 30$ ns, $S = 10$ ns
17
A circuit outputs a digit in the form of $4$ bits. $0$ is represented by $0000$, $1$ by $0001$, …, $9$ by $1001$. A combinational circuit is to be designed which takes these $4$ bits as input and outputs $1$ if the digit $\geq$ $5$, and $0$ otherwise. If only AND, OR and NOT gates may be used, what is the minimum number of gates required? $2$ $3$ $4$ $5$
18
Consider the Boolean function $z(a,b,c)$. Which one of the following minterm lists represents the circuit given above? $z=\sum (0,1,3,7)$ $z=\sum (1,4,5,6,7)$ $z=\sum (2,4,5,6,7)$ $z=\sum (2,3,5)$
1 vote
19
20
A sequential circuit using D flip-flop and logic gates is shown in Figure, where $X$ and $Y$ are the inputs and $Z$ is the output. The circuit is $\text{S-R}$ Flip-flop with inputs $X = R$ and $Y=S$ $\text{S-R}$ Flip-flop with inputs $X = S$ and $Y=R$ $\text{J-K}$ Flip-flop with inputs $X = J$ and $Y=K$ $\text{J-K}$ Flip-flop with inputs $X = K$ and $Y=J$
21
Delay of AND gate = 1ns, FF = 2ns. What is the maximum clock rate possible to apply so that counter will work satisfactorily? a) 143 MHz b) 200 MHz c) 333 MHz
22
plz tell how it take common B’ and B
23
Construct a $16 \times 1$ multiplexer with two $8 \times 1$ and one $2 \times 1$ multiplexers.use the block diagram for the three multiplexers.
24
The digital multiplexer is basically a combination logic circuit to perform the operation AND-AND OR-OR AND-OR OR-AND
25
Which one of the following is the function of a multiplexer? To decode information To select $1$ out of $N$ input data sources and to transmit it to single channel To transmit data on $N$ lines To perform serial to parallel conversion
26
is given ans correct ?
27
How many flip-flops will be complemented in a 10-bit binary ripple counter to reach the next count after the following count? 1001100111; 0011111111;
28
In the sequential circuit shown below, if the initial value of the output $Q_1Q_0$ is $00$. What are the next four values of $Q_1Q_0$? $11$, $10$, $01$, $00$ $10$, $11$, $01$, $00$ $10$, $00$, $01$, $11$ $11$, $10$, $00$, $01$
29
Assume that the EXCLUSIVE-OR gate has a propagation delay of 20ns and that the AND and OR gates have a Propagation delay of 10ns. What is the total Propagation delay time in the four-bit adder of the figure given below?
1 vote
30
31
A 1-bit full adder circuit takes 5 ns to generate the carry-out bit and 10 ns for the sum-bit. When 4, 1-bit full adders are cascaded, the maximum rate of additions per second will be _______ × 107.
32
A $4$ bit ripple counter and a $4$ bit synchronous counter are made using flip-flops having a propagation delay of $10$ ns each. If the worst case delay in the ripple counter and the synchronous counter be $R$ and $S$ respectively, then $R = 10$ ns, $S = 40$ ns $R = 40$ ns, $S = 10$ ns $R = 10$ ns, $S = 30$ ns $R = 30$ ns, $S = 10$ ns
1 vote
33
A decimal has $25$ digits. The number of bits needed for its equivalent binary representation is approximately, $50$ $74$ $40$ $60$
34
How many $2$-input multiplexers are required to construct a $2^{10}$ input multiplexer? $1023$ $31$ $10$ $127$
35
The number of columns in a stateable for a sequential circuit with $’m’$ flip flops and $’n’$ input is $m+n$ $m+2n$ $2m+n$ $2m+2n$
36
A decimal has $25$ digits. The number of bits needed for its equivalent binary representation is approximately, $50$ $74$ $40$ $60$
1 vote
37
The possible number of Boolean function of $3$ variables $X,Y$ and $Z$ such that $f(X,Y,Z) = f(X’,Y’,Z’)$ $8$ $16$ $64$ $32$
1 vote
In a ripple counter using edge triggered $JK$ flip-flops, the pulse input is applied to the clock input of all flip-flops clock input of one flip-flop $J$ and $K$ inputs of all flip-flops $J$ and $K$ inputs of one flip flop
A decimal number has $30$ digits. Approximately, how many digits would the binary representation have? $30$ $60$ $90$ $120$