UART RXC Interrupt

#include <avr/io.h>

#include <avr/interrupt.h>

#include <stdlib.h>

#include "Mainboard_UART_functions.h"

#include <util/delay.h>

unsigned char buffer;

ISR (USART0_RX_vect)

{

  buffer = UART_receive();

  LED2_on();

  _delay_ms(500);

  LED2_off();

  _delay_ms(500);

}

 void UART_Init()

 {

   // baud Calculation: baud = (fosc/ 16*Baudrate)-0.5

   // baud = (20 MHz / 16*9600)-0.5 = 129.708 --> = baud = 130

   unsigned int baud = 130;

   //* Set baud rate */

   UBRR0H = (unsigned char)(baud>>8);

   UBRR0L = (unsigned char)baud;

   /* Enable receiver and transmitter */

   UCSR0B = (1<<RXEN0)|(1<<TXEN0);

   /* Set frame format: 8data, 2stop bit */

   UCSR0C = (1<<USBS0)|(3<<UCSZ00);

   /* Set Interrupts: RXCIE - RX-Complete, TCVIE - TX-Complete */

   UCSR0B = (1<<RXCIE0);

 }

void UART_transmit (unsigned char c) 

{

  while (!(UCSR0A & (1<<UDRE0))) {}      // Wait until UDRE (UART Data Register Empty)- Bit is set.

  UDR0 = c;

}

unsigned char UART_receive (void)        

{

  // while(!(UCSR0A & (1<<RXC0))) {}        // Wait until RXC (Receive Complete) Flag is set.

  return UDR0;

}

int main(void)

{

  /*********************** Initialization ***********************/

  //Port Directions        

  DDRC= 0b01010001;        // SPI Slave select, LEDs                    

  DDRD= 0b00001010;        // UART

  UART_Init();          // UART Initialisierung

  sei();              // Globale Interrupts enable

    while(1)

    {

    UART_transmit(buffer);

    _delay_ms(1000);        

    }

}