Receive and Echo code for MSP430f6438 not working

Hi,

      I am new to MSP.   I cannot find a sample code for 6438, but I do find in the product page, there are sample codes for 663x.

      I tried the receive and Echo code of 663x on 6438. It does not work.

      Anybody help me have a look ? Thanks!

#include <msp430.h>

void Port_Mapping(void);


int main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  while(BAKCTL & LOCKBAK)                    // Unlock XT1 pins for operation
     BAKCTL &= ~(LOCKBAK);
  UCSCTL6 &= ~(XT1OFF);                     // XT1 On
  UCSCTL6 |= XCAP_3;                        // Internal load cap
  // Loop until XT1 fault flag is cleared
  do
  {
    UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
                                            // Clear XT2,XT1,DCO fault flags
    SFRIFG1 &= ~OFIFG;                      // Clear fault flags
  }while (SFRIFG1&OFIFG);                   // Test oscillator fault flag

  Port_Mapping();

  P2SEL |= 0x03;                            // Assign P2.0 to UCA0TXD and...
  P2DIR |= 0x03;                            // P2.1 to UCA0RXD

  UCA0CTL1 |= UCSWRST;                      // **Put state machine in reset**
  UCA0CTL1 |= UCSSEL_1;                     // CLK = ACLK
  UCA0BR0 = 0x03;                           // 32kHz/9600=3.41 (see User's Guide)
  UCA0BR1 = 0x00;                           //
  UCA0MCTL = UCBRS_3+UCBRF_0;               // Modulation UCBRSx=3, UCBRFx=0
  UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
  UCA0IE |= UCRXIE;                         // Enable USCI_A0 RX interrupt

  __bis_SR_register(LPM3_bits + GIE);       // Enter LPM3, interrupts enabled
  __no_operation();                         // For debugger
}

// Echo back RXed character, confirm TX buffer is ready first
#pragma vector=USCI_A0_VECTOR
__interrupt void USCI_A0_ISR(void)
{
  switch(__even_in_range(UCA0IV,4))
  {
  case 0:break;                             // Vector 0 - no interrupt
  case 2:                                   // Vector 2 - RXIFG
    while (!(UCA0IFG&UCTXIFG));             // USCI_A0 TX buffer ready?
    UCA0TXBUF = UCA0RXBUF;                  // TX -> RXed character
    break;
  case 4:break;                             // Vector 4 - TXIFG
  default: break;
  }
}


void Port_Mapping(void)
{
  // Disable Interrupts before altering Port Mapping registers
  __disable_interrupt();
  // Enable Write-access to modify port mapping registers
  PMAPPWD = 0x02D52;

  #ifdef PORT_MAP_RECFG
  // Allow reconfiguration during runtime
  PMAPCTL = PMAPRECFG;
  #endif

  P2MAP0 = PM_UCA0TXD;
  P2MAP1 = PM_UCA0RXD;

  // Disable Write-Access to modify port mapping registers
  PMAPPWD = 0;
  #ifdef PORT_MAP_EINT
  __enable_interrupt();                     // Re-enable all interrupts
  #endif
}

Several more questions. What does the Port_Mapping function exactly do?

Why need XT1 in this case?

Thanks!