ATmega328P datasheet(178/345 Pages) ATMEL

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178

7810A–AVR–11/09

ATmega328P [Preliminary]

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

Receive Complete (RXCn) Flag. When using frames with less than eight bits the most significant

bits of the data read from the UDRn will be masked to zero. The USART has to be initialized

before the function can be used.

Note:

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

For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”

instructions must be replaced with instructions that allow access to extended I/O. Typically

“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.

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

before reading the buffer and returning the value.

19.7.2

Receiving Frames with 9 Data Bits

If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8n bit in

UCSRnB before reading the low bits from the UDRn. This rule applies to the FEn, DORn and

UPEn Status Flags as well. Read status from UCSRnA, then data from UDRn. Reading the

UDRn I/O location will change the state of the receive buffer FIFO and consequently the TXB8n,

FEn, DORn and UPEn bits, which all are stored in the FIFO, will change.

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

characters and the status bits.

Assembly Code Example

(1)

USART_Receive:

; Wait for data to be received

sbis

UCSRnA, RXCn

rjmp

USART_Receive

; Get and return received data from buffer

r16, UDRn

ret

C Code Example(1)

unsigned char

USART_Receive( void )

{

/* Wait for data to be received */

while

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

;

/* Get and return received data from buffer */

return

UDRn;

}

ATmega328P Datasheet(PDF) 178 Page - ATMEL Corporation

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