ATmega325P datasheet(175/364 Pages) ATMEL

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175

8023F–AVR–07/09

ATmega325P/3250P

The following code example shows a simple USART receive function that handles both nine bit

characters and the status bits.

Note:

1. See Section “5.” on page 10.

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

r18, UCSR0A

r17, UCSR0B

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 */

( status & (1<<FE0)|(1<<DOR0)|(1<<UPE0) )

return

-1;

/* Filter the 9th bit, then return */

resh = (resh >> 1) & 0x01;

return

((resh << 8) | resl);

}

ATmega325P 데이터시트(PDF) 175 Page - ATMEL Corporation

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