Multiple choice

Which one of the following holds true when a JK flip-flop is constructed from an SR flip-flop?

  1. S = JQ, R = K + JQ'

  2. J = S, K = R

  3. J = S + R' Q, K = S- (R' + Q' )

  4. S = JQ' , R = KQ
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When constructing a JK flip-flop from an SR flip-flop, we need to prevent the invalid state (S=1, R=1) and enable toggling (J=1, K=1). The correct mapping is S = JQ' and R = KQ. When Q=0, S=J and R=0, so setting J=1 sets Q to 1. When Q=1, S=0 and R=K, so setting K=1 resets Q to 0. When J=K=1 and Q=0, the SR inputs become (1,0) setting Q to 1; when Q=1, they become (0,1) resetting Q to 0 - thus toggling.

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