msp430g2553串口问题

你好！最近在用msp430g2553单片机，遇到串口可以接收数据但是无法发出数据的问题，下面是在proteus上的仿真程序，根据官方例程写的，请大神来指点下，谢谢！急急急。。。

#include <MSP430.h>
#include "LCD.h"
#include "i2c.h"

CHAR BUFF[10] = {'A'};
int main (void)
 {    WDTCTL = WDTPW + WDTHOLD;
    BCSCTL1 = CALBC1_1MHZ;                    // Set DCO
    DCOCTL = CALDCO_1MHZ;
    P1SEL = BIT1 + BIT2 ;                     // P1.1 = RXD, P1.2=TXD
    P1SEL2 = BIT1 + BIT2 ;                     // P1.1 = RXD, P1.2=TXD
    UCA0CTL1 |= UCSSEL_2;                     // SMCLK
    UCA0BR0 = 104;                            // 1MHz 9600
    UCA0BR1 = 0;                              // 1MHz 9600
    UCA0MCTL = UCBRS0;                        // Modulation UCBRSx = 1
    UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
    IE2 |= UCA0RXIE;                          // Enable USCI_A0 RX interrupt
       lcd_init ();
      // Write your code here
    calc_display (BUFF);
    P1DIR |= BIT4;
    P1IE |= BIT0;                             // P1.4 interrupt enabled
    P1IES |= BIT0;                            // P1.4 Hi/lo edge
    P1IFG &= ~BIT0;                           // P1.4 IFG cleared
    _BIS_SR(GIE);
   while (1)
      ;
   return 0;
 }   
 #pragma vector=PORT1_VECTOR
__interrupt void Port_1(void)
{
  P1OUT ^= BIT4;                            // P1.0 = toggle
  P1IFG &= ~BIT0;                           // P1.4 IFG cleared
  while (!(IFG2&UCA0TXIFG));
  UCA0TXBUF = 0X30;
}

#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void)
{
  BUFF[0] = UCA0RXBUF;
  calc_display (BUFF);
  while (!(IFG2&UCA0TXIFG));                // USCI_A0 TX buffer ready?
   UCA0TXBUF = BUFF[0];                    // TX -> RXed character
}