- A parity bit, or check bit is a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value one is even or odd.
- Parity bits are used as the simplest form of error detecting code.
Even Parity Bit
- In the case of even parity, for a given set of bits, the occurrences of bits whose value is 1 is counted.
- If that count is odd, the parity bit value is set to 1, making the total count of occurrences of 1's in the whole set(including the parity bit) an even number.
- If the count of 1's in a given set of bits is already even, the parity bit's value remains 0.
Odd Parity Bit.
- In the case of odd parity, the situation 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 1's 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 remains 0.
| 7 bits of data | (count of 1bits) | 8 bits including parity | |
|---|---|---|---|
| Even | Odd | ||
| 0000000 | 0 | 00000000 | 00000001 |
| 1010001 | 3 | 10100011 | 10100010 |
| 1101001 | 4 | 11010010 | 11010011 |
| 1111111 | 7 | 11111111 | 11111110 |
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