Datasheet

178
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
The following code example shows a simple USART receive function based on polling of the Receive Complete
(RXCn) Flag. When using frames with less than eight bits the most significant bits of the data read from the UDRn
will be masked to zero. The USART has to be initialized before the function can be used.
Note: 1. See ”About code examples” on page 11.
The function simply waits for data to be present in the receive buffer by checking the RXCn Flag, before reading
the buffer and returning the value.
20.7.2 Receiving frames with 9 data bits
If 9-bit characters are used (UCSZ=7), the ninth bit must be read from the RXB8n bit in UCSRnB before reading
the low bits from the UDRn. This rule applies to the FEn, DORn and UPEn Status Flags as well. Read status from
UCSRnA, then data from UDRn. Reading the UDRn I/O location will change the state of the receive buffer FIFO
and consequently the TXB8n, FEn, DORn and UPEn bits, which all are stored in the FIFO, will change.
Assembly code example
(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get and return received data from buffer
in r16, UDR0
ret
C code example
(1)
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get and return received data from buffer */
return UDR0;
}