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+16 votes

Consider the following circuit:


The flip-flops are positive edge triggered D FFs. Each state is designated as a two-bit string $Q_0Q_1$. Let the initial state be 00. The state transition sequence is

in Digital Logic by Veteran (52.1k points)
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After first state (0,0) q0 complement =1 and q1complement=1
next value for q0 is complement so its 1 which is also value for xor and another input is 1 which is value of q1complement so result of xor for (1,1) is 0 there for q1 is 0 and state becomes(1,0) how are you people getting 1,1

(D) is the correct choice!

3 Answers

+26 votes
Best answer

Clearly $Q_{0}$ alternates in every clk cycle as $Q_{0}$$'$ is fed as input and it is D flipflop.

$Q_{1}$ becomes $1$ if its prev value and current $Q_{0}$ differs (EXOR). 

So, the sequence of transitions will be:  $00 -> 11 -> 01 -> 10 -> 00$, (D) choice. 

by Veteran (422k points)
edited by
sir ,answer should be (D) ..

Q0next = D0= Q0'

Q1next = D1= Q0XORQ1'=Q0 XNOR Q1.

Q0Q1 = 00-->11--->01-->10-->00
Yes. I was taking OR Gate. Corrected now. Thanks..
My pleasure ...sir :)
sequence is 00->11->10->01
but i got 00--11--10--01.

your statement : "Q1 becomes 1 if its prev value and current Q0 differs (EXOR)." is wrong i guess as q1 becomes 1 if complement of its prev value and current Qo differs  

how to know about the sequence

 @Arjun sir,

$Q_1$ becomes $1$ if its prev value and current $Q_0$ differs (EXOR).   

 Shouldn't it be $Q_1$ becomes $1$ if the complement of its previous value and previous $Q_0$ differs (EXOR). ?

0 votes
answer - D
by Loyal (8.6k points)
edited by
0 votes

Very clearly, Option D.

by Active (1k points)

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