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In the case of odd parity, the coding is reversed. For a given set of bits, if the count of bits with a value of 1 is even, the parity bit value is set to 1 making the total count of 1s in the whole set (including the parity bit) an odd number. If the count of bits with a value of 1 is odd, the count is already odd so the parity bit's value is 0.
A parity bit is a bit that is added to a group of source bits to ensure that the number of set bits (i.e., bits with value 1) in the outcome is even or odd. It is a very simple scheme that can be used to detect single or any other odd number (i.e., three, five, etc.) of errors in the output.
Each data bit is included in a unique set of 2 or more parity bits, as determined by the binary form of its bit position. Parity bit 1 covers all bit positions which have the least significant bit set: bit 1 (the parity bit itself), 3, 5, 7, 9, etc.
It is normally a single bit in a processor status register. For example, assume a machine where a set parity flag indicates even parity. If the result of the last operation were 26 (11010 in binary), the parity flag would be 0 since the number of set bits is odd. Similarly, if the result were 10 (1010 in binary) then the parity flag would be 1.
Logic parity RAM recalculates an always-valid parity bit each time a byte is read from memory, instead of storing the parity bit when the memory is written to; the calculated parity bit, which will not reveal if the data has been corrupted (hence the name "fake parity"), is presented to the parity-checking logic.
The parity bit in each character can be set to one of the following: None (N) means that no parity bit is sent and the transmission is shortened. Odd (O) means that the parity bit is set so that the number of 1 bits is odd. Even (E) means that the parity bit is set so that the number of 1 bits is even.
Bit 32 is the parity bit, and is used to verify that the word was not damaged or garbled during transmission. Every ARINC 429 channel typically uses "odd" parity - there must be an odd number of "1" bits in the word. This bit is set to 0 or 1 to ensure that the correct number of bits are set to 1 in the word.
In this diagram, one byte is sent, consisting of a start bit, followed by eight data bits (D1-8), and two stop bits, for a 11-bit UART frame. The number of data and formatting bits, the presence or absence of a parity bit, the form of parity (even or odd) and the transmission speed must be pre-agreed by the communicating parties.