Sequential circuits

Question 21

How many pulses are needed to change the contents of a 8-bit up counter from 10101100 to 00100111 (rightmost bit is the LSB)?

• 134

• 133

• 124

• 123

Question 22

Which of the following input sequences will always generate a 1 at the output z at the end of the third cycle?

• 0 0 0 1 0 1 1 1 1

• 1 0 1 1 1 0 1 1 1

• 0 1 1 1 0 1 1 1 1

• 0 0 1 1 1 0 1 1 1

Question 23

We want to design a synchronous counter that counts the sequence 0-1-0-2-0-3 and then repeats. The minimum number of J-K flip-flops required to implement this counter is   Note : This question was asked as Numerical Answer Type.

• 1

• 2

• 4

• 5

Question 24

Which of the following input sequences for a cross-coupled R-S flip-flop realized with two NAND gates may lead to an oscillation ?

• 11, 00

• 01, 10

• 10, 01

• 00, 11

Question 25

The Boolean function f implemented in the figure shown below, using two input multiplexers is:

[caption width="800"] [/caption]

• AB’C + ABC’

• A’B’C + A’BC’

• A’BC + A’B’C’

• ABC + AB’C’

Question 26

A D flip-flop is to be connected to an 8085 microprocessor chip as a 1-bit output port with a port address of FF hex. Data bit D3 should be involved in the data transfer from CPU to the flip-flop. The flip-flop should be cleared on power ON.

• a. Using only one NAND gate (fan in of 10), one NOT gate and one D flip-flop. Draw the required interface logic circuit (only the relevant signals should be shown).
• b. Write a program to generate a square wave on the output of the flip-flop. ON and OFF periods of the square wave should be 7 bus cycles each.

Question 27

Design a synchronous counter to go through the following states: 1, 4, 2, 3, 1, 4, 2, 3, 1, 4,...........

Question 28

Consider the synchronous sequential circuit in the below figure         a) Draw a state diagram, which is implemented by the circuit. Use the following names for the states corresponding to the values of flip-flops as given below.           b) Given that the initial state of the circuit is S4, identify the set of states, which are not reachable.

Question 29

Consider following counters: Counter-1: Counter-2: Which of the following option is correct?

• Counter-1 is a three-bit "counter" which counts 0, 1, 2, 4, 5, 7, 0, ... . and Counter-2 is a three-bit "counter" which counts 0, 3, 6, 1, 4, 7, 2, 5, 0, 3, ... .

• Counter-1 is a three-bit "counter" which counts 0, 2, 6, 1, 4, 7, 2, 5, 0, 2, ... . and Counter-2 is a three-bit "counter" which counts 0, 1, 2, 4, 5, 7, 0, ... .

• Counter-1 is a three-bit "counter" which counts 0, 3, 6, 1, 4, 7, 2, 5, 0, 3, ... . and Counter-2 is a three-bit "counter" which counts 0, 1, 2, 4, 5, 7, 0, ... .

• Counter-1 is a three-bit "counter" which counts 0, 3, 6, 1, 4, 7, 2, 5, 0, 3, ... . and Counter-2 is a three-bit "counter" which counts 0, 1, 2, 3, 5, 6, 0, ... .

Question 30

Consider the following statements regarding counters:

S1 : The Hamming distance of an Overbeck counter is 1 
     and the Hamming distance of a Johnson counter is 2.
S2 : Only output sequence 0, 8, 12, 14, 15, 7, 3, 1, 0, ... is possible 
     in Overbeck counter but not output sequence 2, 1, 8, 4, 2, 1, ...
S3 : A binary counter can represent 2^N states, 
     where N is the number of bits in the code, 
     whereas an Overbeck counter can represent only N states 
     and a Johnson counter can represent only 2N states. 

• Only S1, S2 are false and S3 is true

• Only S2, S3 are false and S1 is true

• Only S1, S3 are false and S2 is true

• All S1, S2, and S3 are true