Datasheet

#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 */
UCSRB = (1<<RXEN)|(1<<TXEN);
/* Set frame format: 8data, 2stop bit */
UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);
}
Note: 1. See About Code Examples.
More advanced initialization routines can be written to 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.
Related Links
About Code Examples on page 19
23.6. 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.
23.6.1. Sending Frames with 5 to 8 Data Bits
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 frame. The Shift Register is
loaded with new data if it is in idle state (no ongoing transmission) or immediately after the last stop bit of
the previous frame is transmitted. When the Shift Register is loaded with new data, it will transfer one
complete frame at the rate given by the Baud Register, U2X bit or by XCK depending on mode of
operation.
The following code examples show a simple USART transmit function based on polling of the Data
Register Empty (UDRE) Flag. When using frames with less than eight bits, the most significant bits
written to the UDR are ignored. The USART has to be initialized before the function can be used. For the
assembly code, the data to be sent is assumed to be stored in Register R16.
Assembly Code Example
(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out UDR,r16
ret
Atmel ATmega32A [DATASHEET]
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