sampling sine wave to detect zero crossing

Hi,

          I need to sample a rectified sine wave of 230V, 50Hz to detect its zero crossing .  but I am finding it difficult to continuously sample it. The code is given below:

void main(void)
{
	
    WDTCTL = WDTPW + WDTHOLD;                  // Stop WDT
    BCSCTL1 = CALBC1_8MHZ;                       // Set range
    DCOCTL = CALDCO_8MHZ; 
    P1DIR |= BIT0;
    P2DIR |=0xF8;         					  // Set ports P2.0/1/2 to Input Direction
    P2SEL |=0x07;         					  // Select Ports P2.0/1/2 as analogue input function
    

  	// Configure the Timer_A in order to trigger the ADC10

  	TA1CCTL0 =CCIE;              			 // Enable the Timer_A interrup
  	TA1CCR0  = 98;           				 // Set Timer_A Capture/Compare Registor to TA_Prd
  	TA1CTL = TASSEL_2 + MC_1;    			 // Select Sub_system Master Clock SMCLK as source of trigger signal
                              				 // Select Up_mode, the timer_A counts up to TACCR0
 
 	// ADC10 COnfiguration

	ADC10CTL0 =ADC10ON + MSC; 				 //ADC ON, Reference Voltage to 2.5 V and select Up-mode
	ADC10CTL1 = INCH_1 +CONSEQ_2;			 // Select A1 as input channel, repeat single channel as conversion sequence
	ADC10DTC0 = ADC10CT; 					 // continuous data transfer


	for (;;){
    	ADC10CTL0 |= ENC + ADC10SC;              	// Sampling and conversion start
    	__bis_SR_register(CPUOFF + GIE);        	 // LPM0, ADC10_ISR will force exit
    		if (ADC10MEM == 0x0000) {

 // some code    			

    		}                          			                                    	  
  	}
  	
}

// Timer A0 interrupt service routine 
#pragma vector=TIMER1_A1_VECTOR
__interrupt void Timer_A1(void){

	 _bis_SR_register_on_exit(CPUOFF);

}