Questions about EZ430_f2013 SD16 module

Hello all,

I was involved in a project which need to use the SD16 module in EZ430_f2013 USB stick. However, when I practiced the code example "msp430x20x3_sd16A_01.c" (as shown below) and downloaded it into my EZ430 stick, I could not get stable SD16MEM0 value (variation was large).

/////////////////////////////////////
#include  <msp430x20x3.h>
void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;   // Stop watchdog timer
  P1DIR |= 0x01;                            // Set P1.0 to output direction
  SD16CTL = SD16REFON + SD16SSEL_1;         // 1.2V ref, SMCLK
  SD16INCTL0 = SD16INCH_1;                  // A1+/-
  SD16CCTL0 =  SD16UNI + SD16IE;            // 256OSR, unipolar, interrupt enable
  //SD16AE = SD16AE2;                    // P1.1 A1+, A1- = VSS
  SD16AE = SD16AE2 + SD16AE3;
  SD16CCTL0 |= SD16SC;            // Set bit to start conversion

  _BIS_SR(LPM0_bits + GIE);
}

#pragma vector = SD16_VECTOR
__interrupt void SD16ISR(void)      // I set a break point here
{
  if (SD16MEM0 < 0x7FFF)  // SD16MEM0 > 0.3V?, clears IFG
    P1OUT &= ~0x01;
  else
    P1OUT |= 0x01;
}
///////////////////////////////////////////

In this example, I think the SD16 can only sense 0v to 0.6volt (please correct me if I am wrong). Therefore, I set up a simple example in which I used a DC supply, 0.6 volt connecting with a series of resistors R1 (1KOhm) and R2 ( 2KOhm) to GND; I fed the R2 voltage (0.4v) and GND into my EZ430 input hole P4 and P5 respectively. When I set a break point in "__interrupt void SD16ISR(void) " and press GO, the SD16MEM0 value I got from each break was not the same, and the value varied from 30000 to 40000. I also thought the SD16MEM0 of 0.6V should be 65535, but I still got an unstable result. Does anyone have any suggestion? 

Thank you all.