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(ii) Parity types and operations
The parity bit is used to detect bit errors in transfer data. Usually, the same type of parity bit is used by the
transmitting and receiving sides. When odd parity or even parity is set, errors in the parity bit (the odd-
number bit) can be detected. When zero parity or no parity is set, errors are not detected.
(a)
Even parity
•
During transmission
The number of bits in transmit data including a parity bit is controlled so that the number is set an
even number of "1" bits. The value of the parity bit is as follows.
If the transmit data contains an odd number of "1" bits : the parity bit value is "1"
If the transmit data contains an even number of "1" bits : the parity bit value is "0"
•
During reception
The number of "1" bits is counted among the receive data including a parity bit, and a parity error is
generated when the result is an odd number.
(b)
Odd parity
•
During transmission
The number of bits in transmit data including a parity bit is controlled so that the number is set an
odd number of "1" bits. The value of the parity bit is as follows.
If the transmit data contains an odd number of "1" bits : the parity bit value is "0"
If the transmit data contains an even number of "1" bits : the parity bit value is "1"
•
During reception
The number of "1" bits is counted among the receive data including a parity bit, and a parity error is
generated when the result is an even number.
(c)
Zero parity
During transmission, the parity bit is set to "0" regardless of the transmit data.
During reception, the parity bit is not checked. Therefore, no parity errors will be generated regardless
of whether the parity bit is a "0" or a "1".
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CHAPTER 10
SERIAL INTERFACE FUNCTION
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