AVRFreaks.net

// The chip is factory set to run on internal
// oscillator at 4 MHz so the value is 4000000UL

OCR2 = ADCH;
      if ( (UCSRA & (1 << UDRE))) // UDRE slot== 1 when the buffer is empty
      {   
         UDR = ADCH;
         
      }

char buffer[4];

itoa(ADCH, buffer, 10); // Convert ADCH to an ASCII string, in decimal

char* bufferPos = &buffer[0]; // Make a pointer to our string
while (*bufferPos != 0x00) // Loop until null terminator found
{
    while(!(UCSRA & (1 << UDRE))); // Wait until buffer empty
    UDR = *bufferPos; // Load next string byte into the USART data register

    bufferPos++; // Advance pointer to next string byte
}

#include <avr/io.h>


void USART_Init(unsigned int baudrate) // UBRR Value not baudrate
{
    // Set baud rate
    UBRR0H = (unsigned char)(baudrate>>8);
    UBRR0L = (unsigned char)baudrate;

   
    // Enable receiver and transmitter
    UCSR0B = (1<<RXEN0)|(1<<TXEN0)|(0<<RXCIE0)|(0<<UDRIE0);

   
}


void Usart_Tx(char data)
{
    while (!(UCSR0A & (1<<UDRE0)));
    UDR0 = data;
}

char Usart_Rx(void)
{
    while (!(UCSR0A & (1<<RXC0)));
    return UDR0;
}

int main(void)
{   
   char c;

   
   
   USART_Init(51);             // Baud rate = 9600bps, 8MHZ, u2x=0

    for (;;)            // Main loop
    {
      c=Usart_Rx();
      Usart_Tx(c);
    } //End Main loop
   
   return 0;
}

// Includes to make the code work
#include <avr/io.h>

// Defines / Declarations
#define F_CPU 16000000UL
#define USART_BAUDRATE 38400UL
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

int main (void)
{
//   char ReceivedByte;

   // Turn on the transmission and reception
   UCSR0B |= (1 << RXEN0) | (1 << TXEN0);
   UCSR0C |= (1 << UCSZ00) | (1 << UCSZ01);

   UBRR0L = BAUD_PRESCALE;
   UBRR0H = (BAUD_PRESCALE >> 8);

   for (;;) // Loop forever
   {
//      while ((UCSR0A & (1 << RXC0)) == 0)
//      {
//      };
//      ReceivedByte = UDR0;

      while ((UCSR0A & (1 << UDRE0)) == 0)
      {      
      };
      
      UDR0 = '0'; // This is hard coded for now
   }   
}

   // Turn on the transmission and reception
   UCSR0B = (1 << RXEN0) | (1 << TXEN0);
   UCSR0C = (1 << UCSZ00) | (1 << UCSZ01);

   // Turn on the transmission and reception
   UCSR0B |= (1 << RXEN0) | (1 << TXEN0);
   UCSR0C |= (1 << UCSZ00) | (1 << UCSZ01);

      UDR0 = 'U'; // This is hard coded for now