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What is the expression for even parity for 3 bits a, b, c ?

  • A.\(a \oplus b \oplus c\)
  • B.\(\overline{a \oplus b \oplus c}\)
  • C.\(a \wedge b \wedge c\)
  • D.\(a \vee b \vee c\)

Answer: A

The expression is \(a \oplus b \oplus c\).

XOR of several bits is 1 when an odd number of them are 1. The even-parity bit must be 1 exactly in those cases, so that data plus parity bit together contain an even number of 1s. So the even-parity generator is \(P = a \oplus b \oplus c\).

Check a = 1, b = 0, c = 0: one 1, so P must be 1 to make the count even, and \(1 \oplus 0 \oplus 0 = 1\). The complement \(\overline{a \oplus b \oplus c}\) is the odd-parity bit. AND and OR of the bits do not track the count of 1s at all.

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