/* UART Transmitter Code */

void init_USART0(){
  volatile uint16_t UBRR_value = 103;  // UBBR0 = ((clock frequency/(16*baud rate)) - 1)
                                       // UBBR0 = ((16,000,000/(16*9600)) -1)  =  103

  UBRR0H = (unsigned char)(UBRR_value >> 8);
  UBRR0L = (unsigned char) UBRR_value;           // Select the 9600 baud rate
  UCSR0B = (1 << RXEN0) | (1 << TXEN0);    // enable Tx and Rx
  UCSR0C = (1 << USBS0) | (3 << UCSZ00);   // set 2 stop bit & 8 data bit
}

void setup() {
  DDRD &= ~4;    // set port-D 2nd pin as Input
  DDRB = 1;      // set port-B 0th pin as Output

 init_USART0();

  while(1){
    if((PIND & 4)==0){
      PORTB ^= 1;

      while(!(UCSR0A & (1 << UDRE0))); // wait untill the UDRE0 bit is set
      UDR0 = 'A';
      for(volatile long i=0; i<100000; i++);  // switch debouncing delay
    }
  }
}

void loop() {}