ATmega64A
The following code example shows a simple USART receive function based on polling of the
Receive Complete n (RXCn) flag. When using frames with less than eight bits the most signifi-
cant 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.
Assembly Code Example(1)
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(1)
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSRnA & (1<<RXCn)) )
;
/* Get and return received data from buffer */
return UDRn;
}
Note:
1. See “About Code Examples” on page 8.
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 (UCSZn=7) the ninth bit must be read from the RXB8n bit in
UCSRnB before reading the low bits from the UDR. This rule applies to the FEn, DORn, and
UPE 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.
184
8160C–AVR–07/09
ATMEL [ ATMEL ]
