ISRO2007-05

Question

The characteristic equation of an $SR$ flip-flop is given by :

• A. $Q_{n+1}=S+RQ_n$
• B. $Q_{n+1}=R\bar{Q}_n + \bar{S}Q_n$
• C. $Q_{n+1}=\bar{S}+RQ_n$
• D. $Q_{n+1}=S+\bar{R}Q_n$

Answer 1

Keep in mind:

characteristic equation of

1. SR Flip flop:Q _next = S+R'Q
2. JK Flip flop: Q _next =JQ'+ K'Q
3. D Flip flop Q _next = D
4. T Flip flop Q _next = T ⊕  Q

Answer :D

Answer 2

Option D 

Characteristic Equation :  Q_n+1 =S+R'Q_n

Characteristic Table

Q_n       S        R         Q_n+1

0              0             0             0

0              0             1             0

0              1             0             1

0              1             1             X

1              0             0             1

1              0             1             0

1              1             0             1

1              1             1             X

By K-map we get Characteristic Equation

Comments

why is Q{n+1} = 0 when Qn = 1, S=0, R=0. Q{n+1} should be 1

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sorry its just a typo when Qn is 1 then Qn+1 is also 1 for S=0,R=0 (memory state)

Thank u

Answer 3

Answer D)

Using K Map we can draw this