Rainbow-electronics ATmega3290P_V Manual de usuario descargar pdf (Pagina 172)

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ATmega329/3290/649/6490

2552H–AVR–11/06

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 8.

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 UCSR0A, RXC0

rjmp USART_Receive

; Get status and 9th bit, then data from buffer

in r18, UCSR0A

in r17, UCSR0B

in r16, UDRn

; 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 = UDRn;

/* 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);

}

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