Datasheet

150
2466T–AVR–07/10
ATmega16(L)
Note: 1. See “About Code Examples” on page 7.
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.
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 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 synchro-
nous operation is used, the clock on the XCK pin will be overridden and used as transmission
clock.
Sending Frames with
5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The
CPU can load the transmit buffer by writing to the UDR I/O location. The buffered data in the
transmit buffer will be moved to the Shift Register when the Shift Register is ready to send a new
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);
}