Rainbow-electronics ATmega8515L Manual de usuario descargar pdf (Pagina 141)

141

ATmega8515(L)

2512A–AVR–04/02

Receiving Frames with 5 to 8

Data Bits

TheReceiverstartsdata reception when it detects avalidstart bit. Each bit that follows

the start bit will be sampled at the baudrate orXCKclock, andshifted into the receive

Shift Register until the first stopbit of a frame isreceived.Asecondstopbit will be

ignoredbythe receiver. When the first stopbit isreceived(i.e., a complete serialframe

ispresent in theReceive Shift Register), the contents of the Shift Registerwill bemoved

into the receive buffer.The receive buffercan then be readbyreading the UDR I/O

location.

The following codeexample shows a simple USART receive function based on polling

of theReceive Complete (RXC) flag. When using frameswithless than eight bits the

most significant bits of the data readfrom the UDR will bemasked to zero. The USART

has to beinitializedbeforethe function can beused.

Note: 1. Theexample codeassumes that the part specificheaderfileis included.

The function simply waitsfordata to be present in the receive bufferbychecking the

RXC flag,before reading the buffer andreturning thevalue.

Assembly Code Example

(1)

USART_Receive:

;

Wait for data to be received

sbis UCSRA, RXC

rjmp USART_Receive

;

Get and return received data from buffer

in r16, UDR

ret

CCode Example

(1)

unsigned char USART_Receive( void )

{

Wait for data to be received

while ( !(UCSRA & (1<<RXC)) )

;

Get and return received data from buffer

return UDR;

}

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Rainbow-electronics ATmega8515L Manual de usuario Pagina 141