Logic circuits

Which circuit activates exactly one of eight outputs according to a 3-bit input?

  1. AEncoder
  2. BDecoder
  3. CCounter
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Answer: B. Decoder

A decoder activates the one of its 2ⁿ outputs that corresponds to an n-bit input. It is used, for example, to select rows and columns from a memory address. A circuit that converts the number of an active input into binary is an encoder.

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  1. 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?
  2. What happens to the value of a binary number when it is shifted left by one bit (assuming no overflow)?
  3. When an even parity bit is added to the 7-bit data 1011001, what is the parity bit?
  4. When is the output of a two-input NOR gate 1?
  5. What is the simplified result of the expression A + A·B?