Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet

181

ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]

Atmel-8271H-AVR- ATmega-Datasheet_08/2014

Note:

1.

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”.

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.

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

USART_Receive:

; Wait for data to be received

in r16, UCSRnA

sbrs r16, UDREn

USART_Receive

; Get and return received data from buffer

r16, UDRn

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;

}