4305438A同过ADC采集外部电池电压的问题

程序如下：

void ADC_init(void)//
{ int i;
  
  P6SEL |= 0x01;    //P60,单通道；
  REFCTL0 |= REFMSTR+REFTCOFF+REFVSEL_2+REFON+REFOUT;////开启REF模块+选2.5V+选择内部参考电压+关闭温度传感器

ADC12CTL0&= ~ADC12ENC;//ENC=0;

  ADC12CTL0 = ADC12ON+ADC12SHT0_4+ADC12MSC+ADC12REFON+ADC12REF2_5V;//;+ADC12SHT1_8 $$$ //开ADC12+采样保持时间+自动采样
                                                        //ADC12REFON+ADC12REF2_5V:基准开启，用2.5V
  ADC12CTL1 = ADC12SHP+ADC12CONSEQ_2; //;ADC12采样/保持脉冲模式：选择信号从“采样定时器”+  ADC12转换顺序选择：2     

  ADC12MCTL0 =ADC12SREF0+ADC12INCH_11;//

  for ( i=0; i<0x30; i++); //
  ADC12IE =ADC12IE0;// 0x01; //    //A0转换结束允许中断。  
  ADC12CTL0 |= ADC12ENC;    //ADC12-A;使能转换。                
  ADC12CTL0 |= ADC12SC;     //ADC12-A启动采样

}

#pragma vector=ADC12_VECTOR//ADC GFY 
__interrupt void ADC12ISR (void)
{ unsigned int voltage;

  switch(__even_in_range(ADC12IV,34))
  {
  case  6:                                  //   ADC12IFG0
   
    voltage=ADC12MEM0;    
    
  LCD_PutChar(voltage);//显示转换值
       
  default: break; 

    }
 
}