User`s manual

8 Serial Port I/O

8-14

eighth bit is used, it must have a value of 0. If the data is based on the extended

ASCII character set, then eight bits must be used since there are 2

or 256

distinct characters.

The Parity Bit

The parity bit provides simple error (parity) checking for the transmitted data.

The types of parity checking are given below.

Mark and space parity checking are seldom used since they offer minimal error

detection. You may choose to not use parity checking at all.

The parity checking process follows these steps:

1 The transmitting device sets the parity bit to 0 or to 1 depending on the data

bit values and the type of parity checking selected.

2 The receiving device checks if the parity bit is consistent with the

transmitted data. If it is, then the data bits are accepted. If it is not, then an

error is returned.

Note Parity checking can detect only 1-bit errors. Multiple-bit errors can

appear as valid data.

For example, suppose the data bits 01110001 are transmitted to your

computer. If even parity is selected, then the parity bit is set to 0 by the

Table 8-2: Parity Types

Parity Type Description

Even The data bits plus the parity bit result in an even number

of 1’s.

Mark The parity bit is always 1.

Odd The data bits plus the parity bit result in an odd number

of 1’s.

Space The parity bit is always 0.