- A parity bit or check bit added to a string of binary code that indicates whether the number of 1-bits in the string is even or odd.
- Parity bits are used as the simplest form of error detecting code.
- There are two types of parity bits even parity and odd parity bit.
Error Detection:
Uses:
- Parity is simple hence it is used in many applications.
- SCSI (Small Computer System Interface) and PCI (Peripheral Component Interconnect) buses use parity to detect transmission errors.
| ASCII-CODE | EVEN-PARITY | ODD-PARITY |
|---|---|---|
| 1000001 | 01000001 | 11000001 |
| 1100001 | 1110001 | 01100001 |
| 1010100 | 11010100 | 01010100 |
| 1111111 | 11111111 | 01111111 |
- In even parity - an even number of errors is undetected.
- In odd parity - an even number of errors is undetected.
| Receiving-end | Parity-error | Sending-end |
|---|---|---|
| Sends back ACK | No | Sends next character |
| Sends back NAK | Yes | Retransmits the character |
- Many microprocessor instruction caches use parity protection.
Notes:
