ATMEGA640 datasheet(211/436 Pages) MICROCHIP

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211

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Note:

1. See “About Code Examples” on page 10.

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

lds

r17, UCSRnA

sbrs

r17, RXCn

rjmp

USART_Receive

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

lds

r18, UCSRnA

lds

r17, UCSRnB

lds

r16, UDRn

; If error, return -1

andi

r18,(1<<FEn)|(1<<DORn)|(1<<UPEn)

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

( !(UCSRnA & (1<<RXCn)) )

;

/* Get status and 9th bit, then data */

/* from buffer */

status = UCSRnA;

resh = UCSRnB;

resl = UDRn;

/* If error, return -1 */

( status & (1<<FEn)|(1<<DORn)|(1<<UPEn) )

return

-1;

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

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

return

((resh << 8) | resl);

}

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