DOC7707 datasheet(157/307 Pages) ETC1

157 / 307 page

157

7707F–AVR–11/10

AT90USB82/162

Note:

1. See “About Code Examples” on page 7.

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

UCSRnA, RXCn

rjmp

USART_Receive

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

r18, UCSRnA

r17, UCSRnB

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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