Datasheet

136
ATmega8A [DATASHEET]
8159E–AVR–02/2013
The following code example shows a simple USART receive function that handles both 9-bit characters and the
status bits.
Note: 1. See “About Code Examples” on page 6.
The receive function example reads all the I/O Registers into the Register File before any computation 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 UCSRA, RXC
rjmp USART_Receive
; Get status and ninth bit, then data from buffer
in r18, UCSRA
in r17, UCSRB
in r16, UDR
; If error, return -1
andi r18,(1<<FE)|(1<<DOR)|(1<<PE)
breq USART_ReceiveNoError
ldi r17, HIGH(-1)
ldi r16, LOW(-1)
USART_ReceiveNoError:
; Filter the ninth 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 ( !(UCSRA & (1<<RXC)) )
;
/* Get status and ninth bit, then data */
/* from buffer */
status = UCSRA;
resh = UCSRB;
resl = UDR;
/* If error, return -1 */
if ( status & (1<<FE)|(1<<DOR)|(1<<PE) )
return -1;
/* Filter the ninth bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}