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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 $Q_1Q_0$?

 

  1. $11$, $10$, $01$, $00$
  2. $10$, $11$, $01$, $00$
  3. $10$, $00$, $01$, $11$
  4. $11$, $10$, $00$, $01$
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10 Answers

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Option A.

$2^{nd}$ flip-flop will be active only when $1^{st}$ flip flop produces output $1.$ For clocks $2$ and $4$ old output is retained by Flip-Flop $2$.

$\begin{array}{c|c}T&Q_{n+1}\\\hline 0&Q_n\\1&\overline{Q_n}\end{array}$$\underset{\text{For rows 2 and 4, Clk for $T_1$ is 0 and hence old o/p is retained}}{\begin{array}{cc|cc}T_0&Q_{0}&T_1&Q_1\\\hline &0&&0\\\hline 1&1&1&1\\1&0&1&1\\1&1&1&0\\1&0&1&0\end{array}}$ $\begin{array}{c|c}Q_1&Q_{0}\\\hline1&1\\1&0\\0&1\\0&0\end{array}$

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answer - A

Initially Q0Q1 = 00

after first clock signal Q0 will be toggled and change to 1. It will activate clock of second FF in sequence and toggle that one as well.

Hence next output Q0Q1=11

Similarly next few sequences for Q0Q1 will be 01, 00

Hence answer sequence Q1Q0 will be 11,10,01,00
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8 votes

Since, Flip Flop T0 is clocked directly from main clock, Q0 will make transitions(toggle as it's T input is 1) whenever the clock pulse goes from 0 to 1 as flip flops are positive edge triggered.

Flip Flop T1's clock is depending on output of Flip Flop T0 which is Q0. Hence, whenever Q0 makes a transition from 0 to 1,Q1, will also make transition(toggle as it's T input is 1) .

As it it clear from timing diagram, the next four values of Q1 Q0 are 11, 10, 01 , 00. Ans (a)

Answer:

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