185
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
Note:
1.
See ”About Code Examples” on page 8.
More advanced initialization routines can be made that include frame format as parameters, dis-
able 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 UCSRnB
Register. When the Transmitter is enabled, the normal port operation of the TxDn pin is overrid-
den 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 syn-
Assembly Code Example
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
#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);
}