Ibm uPD78082 Manuel d'utilisateur télécharger pdf (Page 181)

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CHAPTER 11 SERIAL INTERFACE CHANNEL 2

(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

• Transmission

The number of bits with a value of “1”, including the parity bit, in the transmit data is controlled to

be even.

The value of the parity bit is as follows:

Number of bits with a value of “1” in transmit data is odd: 1

Number of bits with a value of “1” in transmit data is even: 0

• Reception

The number of bits with a value of “1”, including the parity bit, in the receive data is counted. If

it is odd, a parity error occurs.

(ii) Odd parity

• Transmission

Conversely to the situation with even parity, the number of bits with a value of “1”, including the

parity bit, in the transmit data is controlled to be odd. The value of the parity bit is as follows:

Number of bits with a value of “1” in transmit data is odd: 0

Number of bits with a value of “1” in transmit data is even: 1

• Reception

The number of bits with a value of “1”, including the parity bit, in the receive data is counted. If

it is even, a parity error occurs.

(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.

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Ibm uPD78082 Manuel d'utilisateur Page 181