Datasheet

The Parity Error (UPE) Flag indicates that the next frame in the receive buffer had a Parity Error when

received. If Parity Check is not enabled the UPE bit will always read '0'. For compatibility with future

devices, always set this bit to zero when writing to UCSRnA. For more details see Parity Bit Calculation

and 'Parity Checker' below.

21.8.5. Parity Checker

The Parity Checker is active when the high USART Parity Mode bit 1 in the USART Control and Status

is selected by the UCSRnC.UPM[0] bit. When enabled, the Parity Checker calculates the parity of the

data bits in incoming frames and compares the result with the parity bit from the serial frame. The result

of the check is stored in the receive buffer together with the received data and stop bits. The USART

Parity Error Flag in the USART Control and Status Register n A (UCSRnA.UPE) can then be read by

software to check if the frame had a Parity Error.

The UPEn bit is set if the next character that can be read from the receive buffer had a Parity Error when

received and the Parity Checking was enabled at that point (UPM[1] = 1). This bit is valid until the receive

buffer (UDRn) is read.

21.8.6. Disabling the Receiver

In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing receptions

will therefore be lost. When disabled (i.e., UCSRnB.RXEN is written to zero) the Receiver will no longer

override the normal function of the RxDn port pin. The Receiver buffer FIFO will be flushed when the

Receiver is disabled. Remaining data in the buffer will be lost.

21.8.7. Flushing the Receive Buffer

The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer will be emptied of

its contents. Unread data will be lost. If the buffer has to be flushed during normal operation, due to for

instance an error condition, read the UDRn I/O location until the RXCn Flag is cleared.

The following code shows how to flush the receive buffer of USART0.

Assembly Code Example

USART_Flush:

in r16, UCSR0A

sbrs r16, RXC

ret

in r16, UDR0

rjmp USART_Flush

C Code Example

void USART_Flush( void )

{

unsigned char dummy;

while ( UCSR0A & (1<<RXC) ) dummy = UDR0;

}