FCC Technician Exam Question Of The Day (T8D11)

Q) What is a "parity" bit?

A) An extra code element used to detect errors in received data


NJ2X Notes:
A parity bit is used to detect errors in a data transmission.  It is a simple technique.  With "even parity", the number of bits with the value one are counted and then the parity bit is set such that the sum of all the bits is even.  With "odd" parity, the number of bits with the value of one are counted and then a parity bit is set such that the sum of all the bits is odd. 

With even parity, the receiver then checks the parity count and confirms it is even.  If data is received that is not even then the receiver recognizes that an error has occured.

Even Parity Example:
00001111 = 4, parity bit = 0, sum of all bits is even
11001101 = 5, parity bit = 1, sum of all bits is even
11111111 = 8, parity bit = 0, sum of all bits is even
01111111 = 7, parity bit = 1, sum of all bits is even




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