avr_hackery1.c

#include <avr/io.h>
#include <avr/interrupt.h>

#define USART_BAUDRATE 9600

//#define BAUD_PRESCALE ((((F_CPU / 16) + (USART_BAUDRATE / 2) / (USART_BAUDRATE))-1)
#define BAUD_PRESCALE 104

void initialise_UART(void)
{
  UCSR0B = ((1 << RXEN0) | (1 << TXEN0)); // enable TX and RX lines

  UCSR0C = (1 << USBS0) | (3 << UCSZ00); // set 8 data bits, 2 stop bits

  // set higher and lower parts of 16 bit register for setting baud rate
  UBRR0H = (BAUD_PRESCALE >> 8);
  UBRR0L = BAUD_PRESCALE;

  UCSR0B |= (1 << RXCIE0);

  sei();  

}

int main(void)
{

  unsigned int PIN = 5;

  TCCR1B |= ((1 << CS10) | (1 << CS12));
  
  DDRB |= (1 << PIN); // enable LED pin in DDRB register
  
  for (;;){
    if (TCNT1 >= 7812){
      PORTB ^= (1 << PIN); 
      TCNT1 = 0;
    }
  }
  
}


ISR(USART0_RXC_vect)
{
  char byte_received = UDR0;

  

}