NEC mPD789101, User Manual

Page: 184 / 265

CHAPTER 13 SERIAL INTERFACE 20
User’s Manual U13045EJ2V0UM00
184
(b) Parity types and operation
The parity bit is used to detect a bit error in the communication data. Normally, the same kind of parity
bit is used on the transmitting side and the receiving side. With even parity and odd parity, a one-bit (odd
number) error can be detected. With 0 parity and no parity, an error cannot be detected.
(i) Even parity
• At transmission
The transmission operation is controlled so that the number of bits with a value of “1” in the transmit
data including parity bit may be even. The parity bit value should be as follows.
The number of bits with a value of “1” is an odd number in transmit data: 1
The number of bits with a value of “1” is an even number in transmit data: 0
• At reception
The number of bits with a value of “1” in the receive data including parity bit is counted, and if the
number is odd, a parity error is generated.
(ii) Odd parity
• At transmission
Conversely to even parity, the transmission operation is controlled so that the number of bits with
a value of “1” in the transmit data including parity bit may be odd. The parity bit value should be
as follows.
The number of bits with a value of “1” is an odd number in transmit data: 0
The number of bits with a value of “1” is an even number in transmit data: 1
• At reception
The number of bits with a value of “1” in the receive data including parity bit is counted, and if the
number is even, a parity error is generated.
(iii) 0 Parity
When transmitting, the parity bit is set to “0” irrespective of the transmit data.
At reception, a parity bit check is not performed. Therefore, a parity error is not generated, irrespective
of whether the parity bit is set to “0” or “1”.
(iv) No parity
A parity bit is not added to the transmit data. At reception, data is received assuming that there is
no parity bit. Since there is no parity bit, a parity error is not generated.