AN2284 datasheet(34/40 Pages) STMICROELECTRONICS

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9 SC Reader Lib: Parity Error Management

AN2284

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SC Reader Lib: Parity Error Management

In the T=0 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 previously received in error.

9.1

Data Sent From Card to Reader

STR71xx is able to detect via HW a parity error on a received data pulling down the data line

during the stop bit.

9.2

Data Sent From Reader to Card

Vice versa if the smart card pulls down the I/O line to signal that a parity error occurred, the

user needs to check it by SW in order to resend the last data.

The SC library uses the

Uart_ByteSend_SCirq funtion (sc.c file) in conjunction with:

SC_ParityErrorIRQHandler(void) (device_SCR.c file) funtion which checks if the parity error

occurs and manages it.

Each time the

Uart_ByteSend_SCirq function is called it:

- sends a byte

- enables the reception

(UART_RxConfig(UART1 ,ENABLE)) in order to capture the

transmitted byte

- enables the Frame error interrupt source

After a byte is sent from the microcontroller to the card, the smart card peripheral 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 related irq event invokes the

SC_ParityErrorIRQHandler(void) function. It resends the last data and disables the irq

source.

AN2284 Datasheet(PDF) 34 Page - STMicroelectronics