Capturing 840KHz signal using Timer of MSP430G2452

Hi,

I am using MSP430G2452 MCU to capture the 840KHz signal and below mentioned the code. i observed that it is not able to capture this higher frequency. I tried supplying throgh signal generator and noticed that upto 300KHz it capturing and beyond that not.

#include <msp430g2152.h>     
unsigned int new_cap=0;      
unsigned int old_cap=0;      
unsigned int cap_diff=0;     
void main(void)
{
    WDTCTL = WDTPW + WDTHOLD;                     // Stop WDT
    BCSCTL1 = CALBC1_16MHZ;                    // Set Oscillator range
  DCOCTL = CALDCO_16MHZ;
    P1SEL |= BIT2;                                // Port 1.2/TACCR1 - Input                
   P1DIR=0xF0;              // P1.4, P1.5, P1.6, P1.7 as a output
    P1OUT=0x00;       // Initially reset port1                    
  P1OUT |=0x10;      // P1.4 High for Green status LED
    TACTL = TASSEL_2 +MC_2;              // SMCLK = 1 Mhz, continuous mode
    TACCTL1 = CM_1+CCIS_0+SCS+CAP+CCIE;    // capture on rising edge & falling edge, Timer A select, Sync., capture mode, Enable timer interrupt
       
    __bis_SR_register(LPM0_bits + GIE);           // LPM0 mode
}   

// Timer A1 interrupt service routine

#pragma vector = TIMER0_A1_VECTOR
__interrupt void TA1_ISR(void)
{
 switch( TAIV )                                 // Efficient switch-implementation
  {
    case 2:                                     // CCR1 capture value

P1OUT ^= BIT4; //toggling pin4 of PORT 1 and chekcing in CRO
      new_cap = TACCR1;
    cap_diff = new_cap - old_cap;  
     old_cap = new_cap;                          // move current value
   break;                
  }
}

So please let us know is it possible to capture the signal at 840KHz.

Thanks in advance...