ATmega328P datasheet(207/448 Pages) ATMEL

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207

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

be used to check that there are no unread data in the receive buffer. Note that the TXCn Flag

must be cleared before each transmission (before UDRn is written) if it is used for this purpose.

The following simple USART initialization code examples show one assembly and one C func-

tion that are equal in functionality. The examples assume polling (no interrupts enabled). The

baud rate is given as a function parameter. For the assembly code, the baud rate parameter is

assumed to be stored in the r17:r16 registers.

Note:

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

Assembly Code Example

(1)

USART_Init:

clr

r18

out

UBRRnH,r18

out

UBRRnL,r18

; Setting the XCKn port pin as output, enables master mode.

sbi

XCKn_DDR, XCKn

; Set MSPI mode of operation and SPI data mode 0.

ldi

r18, (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn)

out

UCSRnC,r18

; Enable receiver and transmitter.

ldi

r18, (1<<RXENn)|(1<<TXENn)

out

UCSRnB,r18

; Set baud rate.

; IMPORTANT: The Baud Rate must be set after the transmitter is enabled!

out

UBRRnH, r17

out

UBRRnL, r18

ret

C Code Example(1)

void

USART_Init( unsigned int baud )

{

UBRRn = 0;

/* Setting the XCKn port pin as output, enables master mode. */

XCKn_DDR |= (1<<XCKn);

/* Set MSPI mode of operation and SPI data mode 0. */

UCSRnC = (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn);

/* Enable receiver and transmitter. */

UCSRnB = (1<<RXENn)|(1<<TXENn);

/* Set baud rate. */

/* IMPORTANT: The Baud Rate must be set after the transmitter is enabled

UBRRn = baud;

}

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