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185
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
Note:
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.
19.8.2
Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8n bit in UCS-
RnB 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.
The following code example shows a simple USART receive function that handles both nine bit
characters and the status bits.
Assembly Code Example
USART_Receive:
; Wait for data to be received
sbis
UCSRnA, RXCn
rjmp
USART_Receive
; Get and return received data from buffer
in
r16, UDRn
ret
C Code Example
unsigned char
USART_Receive( void )
{
/* Wait for data to be received */
while
( !(UCSRnA & (1<<RXCn)) )
;
/* Get and return received data from buffer */
return
UDRn;
}