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

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  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

Answer (Detailed Solution Below)

Option 4 : 0, 8, 12, 14, 15, 7, 3, 1, 0
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Detailed Solution

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Circuit for Johnson counter:

zza03

From LSB bit complement (Q̅3  ) is fed into MSB(Q0)

Q0 is MSB and Q3 is LSB 

CLK

Q0

Q1

Q2

Q3

Decimal

0(initial)

0

0

0

0

0

1

1

0

0

0

8

2

1

1

0

0

12

3

1

1

1

0

14

4

1

1

1

1

15

5

0

1

1

1

7

6

0

0

1

1

3

7

0

0

0

1

1

8

0

0

0

0

0

Count sequence of 0 → 8 → 12 → 14 → 15 → 7 → 3 → 1 → 0 →  (repeat)

Confusion Point:

If Q3 is MSB and Q0 is LSB

CLK

Q3

Q2

Q1

Q0

Decimal

0(initial)

0

0

0

0

0

1

0

0

0

1

1

2

0

0

1

1

3

3

0

1

1

1

7

4

1

1

1

1

15

5

1

1

1

0

14

6

1

1

0

0

12

7

1

0

0

0

8

8

0

0

0

0

0

 

Count sequence of 0 → 1 → 3 → 7 → 15 →14 →12 → 8 → 0 →  (repeat)

Important Points:

In Anser key. option 4 is given as correct

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