Datasheet

174
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
The following simple USART initialization code examples show one assembly and one C function 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 11.
More advanced initialization routines can be made that include frame format as parameters, disable interrupts and
so on. However, many applications use a fixed setting of the baud and control registers, and for these types of
applications the initialization code can be placed directly in the main routine, or be combined with initialization code
for other I/O modules.
Assembly code example
(1)
USART_Init:
; Set baud rate
out UBRR0H, r17
out UBRR0L, r16
; Enable receiver and transmitter
ldi r16, (1<<RXEN0)|(1<<TXEN0)
out UCSR0B,r16
; Set frame format: 8data, 2stop bit
ldi r16, (1<<USBS0)|(3<<UCSZ00)
out UCSR0C,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 */
UBRR0H = (unsigned char)(ubrr>>8);
UBRR0L = (unsigned char)ubrr;
/* Enable receiver and transmitter */
UCSR0B = (1<<RXEN0)|(1<<TXEN0);
/* Set frame format: 8data, 2stop bit */
UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}