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GATE 2023 IN – Question 42

Digital Electronics · Sequential logic and counters · 2 marks · Multiple choice

In the circuit shown, the initial binary content of shift register A is 1101 and that of shift register B is 1010. The shift registers are positive-edge triggered, and the gates have no delay. When the shift control is high, what will be the binary content of the shift registers A and B after four clock pulses?

Diagram for GATE 2023 IN question 42
  1. A = 1101, B = 1101
  2. A = 1110, B = 1001
  3. A = 0101, B = 1101
  4. A = 1010, B = 1111

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Show answer and explanation

Correct answer: (C) A = 0101, B = 1101

Explanation

The bit entering A is its last bit XOR the complement of its second bit. Evaluate each update from the pre-clock state. The successive (A,B) states are (1110,1101), (0111,0110), (1011,1011), (0101,1101). After four clocks the answer is **A = 0101, B = 1101; C**.