Glossary · Automation fundamentals, platforms and components
Parity
Also known as: Parity bit, Parity check
German: Parität
In data communication and storage, parity is a simple error-detection method that adds a bit (or block) so that the number of 1 bits becomes even or odd. The receiver recalculates it and detects single-bit errors, but cannot correct them or detect every multi-bit error.
- Automation components
In one sentence
Parity adds a check bit so the count of 1 bits is even or odd, letting a receiver detect single-bit errors in serial data or storage.
Example
A Modbus RTU link on RS-485 is set to 19200 baud, 8 data bits, even parity and 1 stop bit on both the master and all slaves.
How it applies
- Commissioning: On serial links such as RS-485, parity (none, even, odd), data bits, stop bits and baud rate must match on every node. A mismatch shows up as framing or parity errors, often counted on the Rx (receive) side.
- Storage: Some RAID (redundant array of independent disks) levels store parity blocks so that data on a failed disk can be reconstructed.
- Documentation: Give the complete serial setting in one line (for example "19200 8E1") in the interface description and the device manual, and explain where the parity setting is changed.
Parity vs. CRC
A parity bit detects any odd number of flipped bits in a character but misses even numbers of errors. A cyclic redundancy check (CRC), used additionally in Modbus RTU frames and most fieldbuses, detects far more error patterns. Parity is therefore a first line of defense, not proof of data integrity.