AN2646 datasheet(35/43 Pages) STMICROELECTRONICS

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AN2646 - Application note

Smartcard interface library: description

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6.4

Parity error management

In the T0 protocol, error handling is performed on each byte by looking at the parity bit. If the

actual parity bit does not correspond to the parity of the transmitted data, then an error must

have occurred; the receiving side signals that it requires the byte to be retransmitted in the

case of detecting a parity error. This is done by holding the I/O line low (normally the I/O line

is set high preceding the transfer of a byte). When the transmitting side detects this, it

resends the byte that was not received correctly.

6.4.1

Data sent from card to reader

STM8S20x is able to detect a parity error on a received data via hardware, by pulling down

the data line during the stop bit.

6.4.2

Data sent from reader to card

The smartcard pulls down the I/O line to signal that a parity error occurred, the STM8S20x is

able to detect a frame error via software. The smartcard library uses the

SC_ParityErrorHandler()

function to check whether a parity error has occurred and,

to manage the error if any.

After a byte is sent from the microcontroller to the card, the smartcard captures the data

sent on the I/O line. If a parity error is detected from the card, the I/O line is pulled down

during the stop bits. A frame error event occurs and the SC_ParityErrorHandler() function

resends the last data.

AN2646 Fiches technique(PDF) 35 Page - STMicroelectronics