#include <msp430x14x.h>

 void int_clk()

 {

   BCSCTL1 &= ~XT2OFF;

   BCSCTL2 |= SELM_2 + SELS;

   do

   {

     IFG1 &= ~OFIFG;

     for(int i=;i<;i++)

       _NOP();

   }while((IFG1 & OFIFG)!=);

   IFG1 &= ~OFIFG;

 }

 void int_usart()

 {

   U0CTL |= SWRST;    //复位串口

   U0CTL |= CHAR;     //8位数据

   U0TCTL |= SSEL1;   //选择SMCLK

   //波特率19200

   U0BR1 = 0X01;

   U0BR0 = 0XA0;

   UMCTL0 = 0XC0;

   ME1 |= UTXE0 + URXE0;   //使能接收和发送

   U0CTL &= ~SWRST;        //清楚串口复位信号

   IE1 |= URXIE0;          //使能接收中断

   P3SEL |= BIT4 + BIT5;

   P3DIR |= BIT4;

 }

 void sent_byte(unsigned char data)

 {

   while((IFG1 & UTXIFG0)==);

   U0TXBUF = data;

 }

 #pragma vector=UART0RX_VECTOR

 __interrupt void UART0(void)

 {

   unsigned char data = ;

   data = U0RXBUF;

   sent_byte(data);

 }

 int main()

 {

   WDTCTL = WDTPW + WDTHOLD;

   int_clk();

   int_usart();

   _EINT();

   return ;

 }

 #include <msp430x14x.h>

 void int_clk()

 {

   BCSCTL1 &= XT2OFF;

   BCSCTL2 |= SELS + SELM_2;

   do

   {

     IFG1 &= ~OFIFG;

     for(int i=;i<;i++)

       _NOP();

   }while((IFG1 & OFIFG)!=);

   IFG1 &= ~OFIFG;

 }

 void int_usart()

 {

   U0CTL |= SWRST;

   U0CTL |= CHAR;

   U0TCTL = SSEL1;

    //

   U0BR1 = 0X03;

   U0BR0 = 0X41;

   U0MCTL = 0X00;

   ME1 |= UTXE0 + URXE0;

   U0CTL &= ~SWRST;

   IE1 |= URXIE0;

   P3SEL |= BIT4 + BIT5;

   P3DIR |= BIT4;

 }

 void send_byte(unsigned char data)

 {

   while((IFG1 & UTXIFG0)==);

   U0TXBUF = data;

 }

 //串口0发送字符串函数

 /*void Print_Str(char *s)

 {

   while(*s != '\0')

   {

     send_byte(*s++);

   }

 }

 */

 #pragma vector=UART0RX_VECTOR

 __interrupt void UART0_RX_ISR(void)

 {

   unsigned char data;

   data = U0RXBUF;

   P6OUT = data;

   send_byte(data);

 }

 void main()

 {

   WDTCTL = WDTPW + WDTHOLD;

   P6DIR = 0XFF;

   P6OUT = 0XFF;

   int_clk();

   int_usart();

   _EINT();

 //  Print_Str("hello!\n");

 }