UART RX Fehler

#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);   // Turn on the transmission and reception circuitry 

   UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1); // Use 8-bit character sizes 

   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 ((UCSRA & (1 << UDRE)) == 0) {};

  UDR = 0xAA;

   for (;;) // Loop forever 

   { 

      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 

   }    

}