MSP430F4270 SD16_A problem

hello all;

now I am using MSP430F4270, and i'd like to measure the voltage of the battery, if the battery low the microcontroller will give warning.

so i just connect power supply with voltage divider resistor(1.5M and 100K) to A4+ channel analog, but when I debug my program with FET, whenever it takes the ADC result the SD16MEM0 values is always 0xFFFF 

when i measure the A4+ pin is only 0.15V, can someone tell me why,

really appreciate for the help,

here is my program..

#include <stdio.h>
#include <math.h>
#include  <msp430x42x0.h>
#include "in430.h"

#define LOW_BAT 0xAEEF

void main( void )
{
  // Stop watchdog timer to prevent time out reset
  WDTCTL = WDTPW + WDTHOLD;
  Init_LCD();                                         // initialize LCD
  Init_Port();                                        // initialize port
                                                      // FLL_CTL0 |= XCAP14PF;
                                                      // Delay(4);
 
  Display_all();                                          // display all character in LCD
  Init_ADC();
  _EINT();                                       // enable interrupts
 
  while(1)
  {
    Display_sign(M,On);
    Measure_Bat();                           //measure ADC value
  }

}

void Init_ADC(void)
{
  unsigned int i;
  SD16AE |= SD16AE4;                              // SD16 External Input Enable 4 (A4+ and A4-)
 
  SD16CCTL0 |= SD16UNI ;      // , Unipolar mode
  SD16INCTL0 |= SD16INCH_4;                        // SD16 Input Channel select A4
  SD16CTL = SD16REFON + SD16SSEL_1;              // SD16 Switch internal Reference(1.2V) on, clock source SMCLK
  //Delay(6);                                         //delay 5 ms for Vref  start up
  for (i = 0; i < 0x3600; i++);

 unsigned int ADCresult;

void Measure_Bat(void)
{
    SD16CCTL0 |= SD16SC;                                     //start conversion
   
    while ((SD16CCTL0 & SD16IFG)==0);
    ADCresult = SD16MEM0;
    SD16CCTL0 &= ~SD16SC;
    if( ADCresult < LOW_BAT )
   {
    Display_sign(Bat,On);
  
   }
   else
   {
    Display_sign(Bat,Off);
  
   }