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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:

  1. 11
  2. 01
  3. 10
  4. 00
in Digital Logic by Boss (20k points)
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2 Answers

+12 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.

by Active (2.4k points)
selected by
0
Good explaination.
0
How is the sequence made?
+6 votes

correct me if wrong!

q0q1

(initial)       00

(1 clock)   10

(2 clock )  01

(3 clock )  11

( 4 clock)  00

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

by Boss (20k points)
0
no i think 11 will be the answer...
0
the sequence which i made is wrong or correct...??
+1
haa  you did wrong.... 00 then 11 then 01 then 10 and again 00...
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
it would be 00 not 11 becoz

after 1 = 11

after 2 = 10

after 3 = 01

after 4 = 00
+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
Yup!
0
and if you consider q0 as MSB then what is seq,.. ? i just want to conform...
0
if q0 is taken as MSB, sequence would be 00, 11, 01, 10, 00.......Again the ans would be 00.
+1
okk  ... i got same one ... but many didnt get same ...so i want to conform by the way thanks :)
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.
0
Could you please elaborate me on this .

how output is being calculated in everystep
+2
@naga

$Q_0$ is changing at each clock pulse and $Q_1$ is changing only when $Q_0$ changes from $0$ to $1$
+1
Thanks Praveen
+1

it is a Asynchronous sequential circuit(because next ff clock depends on previous ff's output), so it will follow a sequence(like 00, 01 , 10 etc)
so here sequence is 

                q1 q0

initially,      0 0

clock 1-     0 1

clock 2-     1 0

clock 3-      1 1

clock 4-      0 0

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