[MSP430] UART-Interrupt wird nicht angesprungen

void uart0::init()

{

  P3DIR &= ~BIT5;       // set P3.5/URXD0 to input

  P3DIR |=  BIT4;       // set P3.4/UTXD0 to output

  P3SEL |=  BIT5|BIT4;  // set P3.5/URXD0 and P3.4/UTXD0 to peripheral

  U0CTL |= SWRST;       // enable software reset

  ME1 |= UTXE0 + URXE0; // switch UART on

  UCTL0 |= CHAR;        // 8N1

  UTCTL0 |= SSEL1;      // use SMCLK

  set_baudrate(9600);   // 9600 is a good default;

  UCTL0 &= ~SWRST;      // disable software reset

  IE1 |= URXIE0;        // enable rx-interrupt

}

void uart0::set_baudrate(int baudrate)

{

  U0CTL |= SWRST; // enable software reset

  int ubr = F_CPU/baudrate;

  U0BR0 = ubr & 0x00FF;

  U0BR1 = (ubr & 0xFF00) >> 8;

  U0MCTL = (int)(((float)F_CPU/(float)baudrate-(float)ubr)*8.0+0.5);

  UCTL0 &= ~SWRST; // disable software reset

}

while(1)

{

  while(!(IFG1 & URXIFG0)); // ready?

  lcd_puc(RXBUF0);

}

interrupt (UART0RX_VECTOR) usart0_rx(void)

{

  lcd_putc(RXBUF0);

}