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52 votes
52 votes

Consider a $4$-bit Johnson counter with an initial value of $0000.$ The counting sequence of this counter is 

  1. $0, 1, 3, 7, 15, 14, 12, 8, 0$
  2. $0, 1, 3, 5, 7, 9, 11, 13, 15, 0$
  3. $0, 2, 4, 6, 8, 10, 12, 14, 0$
  4. $0, 8, 12, 14, 15, 7, 3, 1, 0$
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7 Answers

Best answer
34 votes
34 votes

$\text{Johnson Counter}$ is a switch‐tail ring counter in which a circular shift register with the complemented output of the last flip‐flop connected to the input of the first flip‐flop.

(D) is the correct answer!

selected by
24 votes
24 votes

option D

0000 - 0

1000 - 8

1100 - 12

and so on.

http://en.wikipedia.org/wiki/Ring_counter

19 votes
19 votes

Counting procedure of a Johnson's Counter

  1. Starting from all 0's , each shift operation inserts 1's from the left until the register is filled with all 1's.
  2. When the register has all 1s,each shift operation inserts 0's from the left until the register is filled with all 0's.
  3. Go to step 1.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------

0000 $\rightarrow$ ${\color{Red} 1}$000 $\rightarrow$ ${\color{Red} 1}{\color{Red} 1}$00 $\rightarrow$  ${\color{Red} 1}{\color{Red} 1}{\color{Red} 1}$0 $\rightarrow$  ${\color{Red} 1}{\color{Red} 1}{\color{Red} 1}{\color{Red} 1}$ $\rightarrow$  ${\color{Blue} 0}{\color{Red} 1}{\color{Red} 1}{\color{Red} 1}$ $\rightarrow$ ${\color{Blue} 0}{\color{Blue} 0}{\color{Red} 1}{\color{Red} 1}$ $\rightarrow$  ${\color{Blue} 0}{\color{Blue} 0}{\color{Blue} 0}{\color{Red} 1}$ $\rightarrow$ ${\color{Blue} 0}{\color{Blue} 0}{\color{Blue} 0}{\color{Blue} 0}$

OR

0 $\rightarrow$ 8 $\rightarrow$ 12 $\rightarrow$ 14 $\rightarrow$ 15 $\rightarrow$ 7 $\rightarrow$ 3 $\rightarrow$ 1 $\rightarrow$ 0

--------------------------------------------------------------------------------------------------------------------------------------------------------------------

$\therefore$ Option D is correct answer.

4 votes
4 votes
Johnson counter is ring counter hence after period of clock cycles its output will repeat .

here 0000 is given as initial state and hence 1 is given as preset in first flipflop and then this one is propagated to consecutive flipflops producing

1000

1100

1110

1111

0111

0011

0001

0000

as output .
Answer:

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