Editing Serial port (section)

===Parity===
{{Main|Parity bit}}

''Parity'' is a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. Correct parity does not necessarily indicate absence of corruption as a corrupted transmission with an even number of errors will pass the parity check. A single parity bit does not allow implementation of [[error correction]] on each character, and [[communication protocol]]s working over serial data links will typically have higher-level mechanisms to ensure data validity and request retransmission of data that has been incorrectly received.

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.
* '''Mark (M)''' parity means that the parity bit is always set to the mark signal condition (1 bit value).
* '''Space (S)''' parity always sends the parity bit in the space signal condition (0 bit value).

Aside from uncommon applications that use the last bit (usually the 9th) for some form of addressing or special signaling, mark or space parity is uncommon, as it adds no error detection information.

Odd parity is more useful than even parity since it ensures that at least one state transition occurs in each character, which makes it more reliable at detecting errors like those that could be caused by serial port speed mismatches. The most common parity setting, however, is ''none'', with error detection handled by a communication protocol.

To allow detection of messages damaged by [[line noise]], electromechanical teleprinters were arranged to print a special character when received data contained a parity error.