关于MSP430G2553 串口无法接受问题 请大家帮忙看一下

首先  我用的 是官方的例程    并且板子上有关于RXD  和TXD的跳线帽也已经改成了HW模式    但是进不了串口中断啊   也并不是所有的时候都进不去 可能有某一次收发就挺正常的  我以为是板子和电脑或者串口软件  的问题 可是在我换了一个板子和电脑还有串口软件 时候 还是这样 实在不知道是怎么回事了 求各位帮帮忙呀  有可能是哪里的问题啊  拜谢！！！下面是官方的代码

//******************************************************************************
//   MSP430G2xx3 Demo - USCI_A0, Ultra-Low Pwr UART 9600 String, 32kHz ACLK
//
//   Description: This program demonstrates a full-duplex 9600-baud UART using
//   USCI_A0 and a 32kHz crystal.  The program will wait in LPM3, and will
//   respond to a received 'u' character using 8N1 protocol. The response will
//   be the string 'Hello World'.
//   ACLK = BRCLK = LFXT1 = 32768Hz, MCLK = SMCLK = DCO ~1.2MHz
//   Baud rate divider with 32768Hz XTAL @9600 = 32768Hz/9600 = 3.41
//* An external watch crystal is required on XIN XOUT for ACLK *//
//
//                MSP430G2xx3
//             -----------------
//         /|\|              XIN|-
//          | |                 | 32kHz
//          --|RST          XOUT|-
//            |                 |
//            |     P1.2/UCA0TXD|------------>
//            |                 | 9600 - 8N1
//            |     P1.1/UCA0RXD|<------------
//
//   D. Dang
//   Texas Instruments Inc.
//   February 2011
//   Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10
//******************************************************************************
#include <msp430.h>

const char string1[] = { "Hello World\r\n" };
unsigned int i;

int main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  P1DIR = 0xFF;                             // All P1.x outputs
  P1OUT = 0;                                // All P1.x reset
  P2DIR = 0xFF;                             // All P2.x outputs
  P2OUT = 0;                                // All P2.x reset
  P1SEL = BIT1 + BIT2 ;                     // P1.1 = RXD, P1.2=TXD
  P1SEL2 = BIT1 + BIT2 ;                     // P1.1 = RXD, P1.2=TXD
  P3DIR = 0xFF;                             // All P3.x outputs
  P3OUT = 0;                                // All P3.x reset  
  UCA0CTL1 |= UCSSEL_1;                     // CLK = ACLK
  UCA0BR0 = 0x03;                           // 32kHz/9600 = 3.41
  UCA0BR1 = 0x00;                           //
  UCA0MCTL = UCBRS1 + UCBRS0;               // Modulation UCBRSx = 3
  UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
  IE2 |= UCA0RXIE;                          // Enable USCI_A0 RX interrupt
  __bis_SR_register(LPM3_bits + GIE);       // Enter LPM3 w/ int until Byte RXed
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCIAB0TX_VECTOR
__interrupt void USCI0TX_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCIAB0TX_VECTOR))) USCI0TX_ISR (void)
#else
#error Compiler not supported!
#endif
{
  UCA0TXBUF = string1[i++];                 // TX next character

  if (i == sizeof string1 - 1)              // TX over?
    IE2 &= ~UCA0TXIE;                       // Disable USCI_A0 TX interrupt
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCIAB0RX_VECTOR))) USCI0RX_ISR (void)
#else
#error Compiler not supported!
#endif
{
  if (UCA0RXBUF == 'u')                     // 'u' received?
  {
    i = 0;
    P1OUT ^= 0x01;     
    IE2 |= UCA0TXIE;                        // Enable USCI_A0 TX interrupt
    UCA0TXBUF = string1[i++];
  }
}