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GATE 2014 CS (CS3) – Question 55

Digital Logic · Sequential Circuits · 2 marks · Multiple choice

The synchronous JK flip-flop circuit shown starts with Q₂Q₁Q₀ = 000. Find the state sequence for the next three clock cycles.

Diagram for GATE 2014 CS (CS3) question 55
  1. 001, 010, 011
  2. 111, 110, 101
  3. 100, 110, 111
  4. 100, 011, 001

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Show answer and explanation

Correct answer: (C) 100, 110, 111

Explanation

Use Qnext=JQ̄+K̄Qand evaluate every flip-flop from the same old state. The connections give Q1next=Q2andQ0next=Q1∨Q0; J2=Q̄1,K2=Q0. Starting000, successive states are **100,110,111,C**. Updating one stage early would incorrectly model a ripple circuit.