
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:
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.
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
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);
}