Datasheet

24.7.1 Receiving Frames with 5 to 8 Data Bits

The Receiver starts data reception when it detects a valid start bit. Each bit that follows the start bit will be

sampled at the baud rate or XCK clock, and shifted into the Receive Shift Register until the first stop bit of

a frame is received. A second stop bit will be ignored by the Receiver. When the first stop bit is received

(i.e., a complete serial frame is present in the Receive Shift Register), the contents of the Shift Register

will be moved into the receive buffer. The receive buffer can then be read by reading the UDR I/O

location.

The following code example shows a simple USART receive function based on polling of the Receive

Complete (RXC) Flag. When using frames with less than eight bits the most significant bits of the data

read from the UDR will be masked to zero. The USART has to be initialized before the function can be

used.

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

C Code 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;

}

Note: 1. See About Code Examples.

The function simply waits for data to be present in the receive buffer by checking the

RXC Flag, before reading the buffer and returning the value.