AVRFreaks.net

#define F_CPU 7372800
#include <avr/io.h>

#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

int main (void)
{

   char ReceivedByte;
   UCSRB |= (1<<RXEN) | (1<<TXEN); // Enable USART Tx & Rx
   UCSRC |= (1<<UCSZ0) | (1<<UCSZ1); // Set serial mode as 8 bit, 1 data bits


   UBRRL = BAUD_PRESCALE; // Load lower 8-bits of the baud rate value into the low byte of the UBRR register
   UBRRH = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value into the high byte of the UBRR register

   while(1)
   {
       while ((UCSRA & (1 << RXC)) == 0) {}; // Do nothing until data have been recieved and is ready to be read from UDR
       ReceivedByte = UDR; // Fetch the recieved byte value into the variable "ByteReceived"

      while ((UCSRA & (1 << UDRE)) == 0) {}; // Do nothing until UDR is ready for more data to be written to it
      UDR = ReceivedByte; // Echo back the received byte back to the computer
   }   
}

#define FOSC 1843200 // Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
void USART_Init( unsigned int ubrr)
{
    UBRR0H = (unsigned char)(ubrr>>8);
    UBRR0L = (unsigned char)ubrr;
    //UCSR0A = 0x00;
    /*Enable receiver and transmitter */
    UCSR0B = (1<<RXEN0)|(1<<TXEN0);
    /* Set frame format: 8data, 2stop bit */
    UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}
void USART_Transmit( unsigned char data )
{
    /* Wait for empty transmit buffer */
    while ( !( UCSR0A & (1<<UDRE0)) )
    ;
    /* Put data into buffer, sends the data */
    UDR0= data;
}

while(1)
{
     //PORTC=0x00;
     USART_Transmit('p');
}

#define FOSC 1843200 // Clock Speed

#include <avr/io.h>
#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((4000000 / (USART_BAUDRATE * 16UL))) - 1)


int main (void)
{
   char ReceivedByte;

   UCSRB |= (1 << RXEN) | (1 << TXEN); // Turn on the transmission and reception circuitry
   
   UCSRC = (1<<URSEL)|(1<<UCSZ0)|(1<<UCSZ0);    /* Set frame format: 8data, 1stop bit */

   UBRRL = BAUD_PRESCALE;

   UBRRH = (BAUD_PRESCALE >> 8);

   for(;;)
   {
      while((UCSRA & (1<< RXC)) == 0) {};

      ReceivedByte = UDR;   // fetch back byte
      
      while ((UCSRA & (1 << UDRE)) == 0) {};    //Wait for UDR, when ready more data can be written

      UDR = ReceivedByte;   //echo back byte

   }



}