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+7 votes

What are the final values of $Q_1$ and $Q_0$ after 4 clock cycles, if initial values are 00 in the sequential circuit shown below:

- 11
- 01
- 10
- 00

+13 votes

Best answer

**Answer:** (d)

**Explanation:**

- T flip flop toggles the state if input T is 1, and does not change state if input T is 0.
- T flip flop is a clocked (synchronous or edge-triggered) flip flop.
- Edge triggered flip flops can only change its values at the edge of a clock,
**in absence of edge does not change its state**, remains same. - In given circuit, clock symbol is showing that it is positive edge triggering (low to high change). Note that there are mainly four different types of clock-triggering methods.

Now, we need to find out Q0Q1 after 4 clock cycles.
**Initial: 00** States Q0 and Q1 are zero
**Clock 1: 11 **State Q0 changed to 1 because input T is 1 and previous state was 0 and State Q1 changed to 1 because input T is 1 and previous state was 0.
**Clock 2: 01 **State Q0 changed to 0 because input T is 1 and previous state was 1 and State Q1 remains same because clk value is 0.
**Clock 3: 10** State Q0 changed to 1 because input T is 1 and previous state was 0 and State Q1 changed to 0 because input T is 1 and previous state was 1.
**Clock 4: 00** State Q0 changed to 0 because input T is 1 and previous state was 1 and State Q1 remains same because clk value is 0.

+6 votes

correct me if wrong!

q_{0}q_{1}

(initial) 00

(1 clock) 10

(2 clock ) 01

(3 clock ) 11

( 4 clock) 00

this will be answer.............

0

and if i consider q1 as MSB and q0 as LSB then it will be 00 -->11-->10-->01 -->00 so its mod 4 down counter . but in both cases after 4th clock it will be 11.

+1

yes i got same sequence ... 00 -->11 -->10--->01-->00 but i confused after 4th clock means o/p or state ... but i have cleared ... by the way you assumed q1 as MSB naa

0

The second flip flop is positive triggered. So I think it will never receive 1 as clock so it will not be activated.So output of second flip flop will be 0 and as 1 is supplied to first toggle flip flop it will always output 0.So answer should be 0.

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