Datasheet

ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
162
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.
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 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
(1)
USART_Receive:
; Wait for data to be received
in r16, UCSRnA
sbrs r16, UDREn
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 7.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions
must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined
with “SBRS”, “SBRC”, “SBR”, and “CBR”.