Logic circuits

When is the output of a three-input majority circuit 1?

  1. AOnly when all three inputs are 1
  2. BWhen two or more of the three inputs are 1
  3. CWhen any input is 1
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Answer: B. When two or more of the three inputs are 1

A majority circuit outputs 1 when more than half of its inputs are 1. With three inputs, that means two or more. Its logic expression is AB + BC + CA, the same as the carry output of a full adder. It is also used in redundant systems to mask the effect of a failure by majority vote.

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  3. What is a typical use of a shift register, which chains flip-flops in series and moves data one bit to the next on each clock?
  4. What happens to the value of a binary number when it is shifted left by one bit (assuming no overflow)?
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