Datasheet

131
ATmega8A [DATASHEET]
8159E–AVR–02/2013
assumed to be stored in the r17:r16 Registers. When the function writes to the UCSRC Register, the URSEL bit
(MSB) must be set due to the sharing of I/O location by UBRRH and UCSRC.
Note: 1. See “About Code Examples” on page 6.
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.
20.6 Data Transmission – The USART Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRB Register. When the
Transmitter is enabled, the normal port operation of the TxD pin is overridden by the USART and given the function
as the Transmitter’s serial output. The baud rate, mode of operation and frame format must be set up once before
doing any transmissions. If synchronous operation is used, the clock on the XCK pin will be overridden and used
as transmission clock.
Assembly Code Example
(1)
USART_Init:
; Set baud rate
out UBRRH, r17
out UBRRL, r16
; Enable receiver and transmitter
ldi r16, (1<<RXEN)|(1<<TXEN)
out UCSRB,r16
; Set frame format: 8data, 2stop bit
ldi r16, (1<<URSEL)|(1<<USBS)|(3<<UCSZ0)
out UCSRC,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 */
UBRRH = (unsigned char)(ubrr>>8);
UBRRL = (unsigned char)ubrr;
/* Enable receiver and transmitter */
UCSRB = (1<<RXEN)|(1<<TXEN);
/* Set frame format: 8data, 2stop bit */
UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);
}