ATmega64A datasheet(180/392 Pages) ATMEL

180 / 392 page

180

8160C–AVR–07/09

ATmega64A

Transmitter or the Receiver depending on the usage. For interrupt driven USART operation, the

Global Interrupt Flag should be cleared (and interrupts globally disabled) when doing the

initialization.

Before doing a re-initialization with changed baud rate or frame format, be sure that there are no

ongoing transmissions during the period the registers are changed. The TXCn flag can be used

to check that the Transmitter has completed all transfers, and the RXCn flag can 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 asynchronous operation using polling

(no interrupts enabled) and a fixed frame format. 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 8.

Assembly Code Example(1)

USART_Init:

; Set baud rate

out

UBRRnH, r17

out

UBRRnL, r16

; Enable receiver and transmitter

ldi

r16, (1<<RXENn)|(1<<TXENn)

out

UCSRnB,r16

; Set frame format: 8data, 2stop bit

ldi

r16, (1<<USBSn)|(3<<UCSZn0)

out

UCSRnC,r16

ret

C Code Example

(1)

#define FOSC 1843200// Clock Speed

#define BAUD 9600

#define MYUBRR FOSC/16/BAUD-1

void

main( void )

{

USART_Init ( MYUBRR );

}

void

USART_Init( unsigned int ubrr )

{

/* Set baud rate */

UBRRnH = (unsigned char)(ubrr>>8);

UBRRnL = (unsigned char)ubrr;

/* Enable receiver and transmitter */

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

/* Set frame format: 8data, 2stop bit */

UCSRnC = (1<<USBSn)|(3<<UCSZn0);

}

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