MSP430G2553 I2C funktioniert nicht

#include <msp430.h>

unsigned char TXData;

unsigned char TXByteCtr;

int main(void)

{

  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  P1SEL |= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0

  P1SEL2|= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0

  UCB0CTL1 |= UCSWRST;                      // Enable SW reset

  UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;     // I2C Master, synchronous mode

  UCB0CTL1 = UCSSEL_2 + UCSWRST;            // Use SMCLK, keep SW reset

  UCB0BR0 = 12;                             // fSCL = SMCLK/12 = ~100kHz

  UCB0BR1 = 0;

  UCB0I2CSA = 0x48;                         // Slave Address is 048h

  UCB0CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation

  IE2 |= UCB0TXIE;                          // Enable TX interrupt

  TXData = 0x00;                            // Holds TX data

  while (1)

  {

    TXByteCtr = 1;                          // Load TX byte counter

    while (UCB0CTL1 & UCTXSTP);             // Ensure stop condition got sent

    UCB0CTL1 |= UCTR + UCTXSTT;             // I2C TX, start condition

    __bis_SR_register(CPUOFF + GIE);        // Enter LPM0 w/ interrupts

                                            // Remain in LPM0 until all data

                                            // is TX'd

    TXData++;                               // Increment data byte

  }

}

//------------------------------------------------------------------------------

// The USCIAB0TX_ISR is structured such that it can be used to transmit any

// number of bytes by pre-loading TXByteCtr with the byte count.

//------------------------------------------------------------------------------

#pragma vector = USCIAB0TX_VECTOR

__interrupt void USCIAB0TX_ISR(void)

{

  if (TXByteCtr)                            // Check TX byte counter

  {

    UCB0TXBUF = TXData;                     // Load TX buffer

    TXByteCtr--;                            // Decrement TX byte counter

  }

  else

  {

    UCB0CTL1 |= UCTXSTP;                    // I2C stop condition

    IFG2 &= ~UCB0TXIFG;                     // Clear USCI_B0 TX int flag

    __bic_SR_register_on_exit(CPUOFF);      // Exit LPM0

  }

}