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In asynchronous communication systems, odd parity refers to parity checking modes, where each set of transmitted bits has an odd number of bits. If the total number of ones in the data plus the parity bit is an odd number of ones, it is called odd parity. If the data already has an odd number of ones, the value of the added parity bit is 0, otherwise it is 1.
Parity bits are the simplest form of error detection. Odd parity checking is used in testing memory storage devices. The sender and receiver should agree to the use odd parity checking. Without this, successful communication is not possible. If an odd number of bits are switched during transmission, parity checks can detect that the data is corrupted. However, the method will fail to detect errors introduced when an even number of bits in the same data unit is altered, as the parity will still remain odd despite data corruption.
Parity bits are added to transmitted messages to ensure that the number of bits with a value of one in a set of bits add up to even or odd numbers. Even and odd parities are the two variants of parity checking modes.
Odd parity can be more clearly explained through an example. Consider the transmitted message 1010001, which has three ones in it. This is turned into odd parity by adding a zero, making the sequence 0 1010001. Thus, the total number of ones remain at three, an odd number. If the transmitted message has the form 1101001, which has four ones in it, this can be turned into odd parity by adding a one, making the sequence 1 1101001.