MSP430G2453 I2C通讯问题

本人在用MSP430G2453搭配BQ76930调试硬件I2C通讯，现在的情况是在不能写数据到BQ的寄存器里面，有时候可以写进去但读不出来数据，请各位高手指点，谢谢
代码如下：
unsigned char SA=0x08;    //从器件地址bq76930_03DBTR
unsigned char RX_BUF;     //接收数据
unsigned char TX_Byc=2;

void i2c_init (void)
  {
     P1SEL2 = BIT6 | BIT7;
     P1SEL =  BIT6 | BIT7;
     P1DIR =  BIT6 | BIT7;
     P1OUT &= ~(BIT6 | BIT7);
     
     UCB0CTL1 |= UCSWRST;                // enable SW reset
     UCB0CTL0 = UCMST+UCMODE_3+UCSYNC ; // I2C Master, synchronous mode
     UCB0CTL1 = UCSSEL_2+UCSWRST;       // Use SMCLK, keep SW reset
     UCB0BR0 = 20;          //fscl=SMCLK/12=~100KHz
     UCB0BR1 = 0;
     UCB0I2CSA = SA;        //set slave address
     UCB0CTL1 &= ~UCSWRST;  //clear SW reset
  }
void I2C_WriteData(unsigned char address,unsigned char data)
  {
     while(UCB0CTL1&UCTXSTP);//确认停止   
     while (UCB0STAT & UCBBUSY); //检测BUS是否空闲 繁忙UCBBUSY=1
     UCB0CTL1 |= UCTR;   //I2C 发送
     IFG2 &= ~UCB0TXIFG;
     UCB0CTL1 |= UCTXSTT;   //启动I2C
     while((IFG2&UCB0TXIFG)==0);
     UCB0TXBUF = address;
     while(UCB0CTL1 & UCTXSTT);
     while((IFG2&UCB0TXIFG)==0);
     UCB0TXBUF = data;
     while((IFG2&UCB0TXIFG)==0);     
     UCB0CTL1 |= UCTXSTP ;
     IFG2 &= ~UCB0TXIFG;
  }
unsigned char I2C_ReadData(unsigned char BQ_address)
  {
  //  IE2 |= UCB0RXIE;      //enable read interrupt
    i2c_init();
    while (UCB0STAT & UCBBUSY);             // Ensure stop condition got sent
    UCB0CTL1 |= UCTR + UCTXSTT;             // I2C TX, start condition
   
    while((IFG2 & UCB0TXIFG)==0);
    UCB0TXBUF = BQ_address;////eeprom low addr
    if(UCB0STAT&UCNACKIFG)    //检测UCNACKIFG:1 需要重新发送
         {
           UCB0CTL1 |= UCTR + UCTXSTT;    // I2C TX, start condition
           while((IFG2&UCB0TXIFG)==0); // Wait USCI_B0 TX  flag Flag reset automaticall
           UCB0TXBUF = BQ_address;// Load TX buffer
         }
    while((IFG2 & UCB0TXIFG)==0);   
    IFG2 &= ~UCB0TXIFG;
   
    UCB0CTL1 &= ~UCTR;        // I2C RX,
    delay_us(10);  
    while (UCB0CTL1 & UCTXSTP);// 判断总线是否被释放
    UCB0CTL1 |= UCTXSTT;           // Start condition
    while((UCB0CTL1&UCTXSTT)==1);  
    RX_BUF = UCB0RXBUF;   
    UCB0CTL1 |= UCTXSTP + UCTXNACK;
   while((UCB0CTL1 & UCTXSTP)==1);
    return (RX_BUF);
  }