Datasheet

169
2570N–AVR–05/11
ATmega325/3250/645/6450
The following code example shows a simple USART receive function that handles both nine bit
characters and the status bits.
Note: 1. See “About Code Examples” on page 9.
The receive function example reads all the I/O Registers into the Register File before any com-
putation is done. This gives an optimal receive buffer utilization since the buffer location read will
be free to accept new data as early as possible.
Assembly Code Example
(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
in r18, UCSR0A
in r17, UCSR0B
in r16, UDR0
; If error, return -1
andi r18,(1<<FE0)|(1<<DOR0)|(1<<UPE0)
breq USART_ReceiveNoError
ldi r17, HIGH(-1)
ldi r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr r17
andi r17, 0x01
ret
C Code Example
(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSR0A;
resh = UCSR0B;
resl = UDR0;
/* If error, return -1 */
if ( status & (1<<FE0)|(1<<DOR0)|(1<<UPE0) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}