用按键控制LED灯的亮灭，当按键按下时，LED灯亮，当按键松开时，LED灯灭。
#include"msp430f6638.h"
unsigned char flag;
void main(void)
{
WDTCTL = WDTPW+WDTHOLD;   // Stop WDT
P4DIR &=~(BIT2);
P4DIR |= BIT4+BIT5+BIT6;   // P4.4,P4.5,P4.6 set as output
P4OUT &=~(BIT4+BIT5+BIT6);   memory按键是什么意思// set led off
P2IE |= BIT6;           // enable P2.6 interrupt
P2IFG &= ~(BIT6);     // clean interrupt flag
__enable_interrupt();   // enable interrupt
while(1)
{ if((P4IN & 0x04)==0)
{ P2IFG |= BIT6;}
else
{P2IFG &=~BIT6;}}
}                        // PORT2 interrupt service routine
#pragma vector=PORT2_VECTOR
__interrupt void port_2(void)
{P4OUT ^=(BIT4+BIT5+BIT6);     // set led on
P2IFG &=~BIT6;                 // clean interrupt flag}
用按键控制LED灯的亮灭，当按键按下时，LED灯亮，当按键松开时，LED灯灭。(查询)
#include"msp430f6638.h"
void main(void)
{WDTCTL = WDTPW+WDTHOLD;             // Stop WDT
                                            //setting direction
P4DIR &= ~(BIT2);                         //setting IO for input
P4DIR |= BIT4+BIT5+BIT6;                 // P4.4,P4.5,P4.6 set as output
while (1)
{if ((P4IN & 0x04) == 0)                   //If key is pressed
{P4OUT |= BIT4+BIT5+BIT6;           //led on}
else{P4OUT &=~(BIT4+BIT5+BIT6);     // led off}}}
将ACLK配置为VLOCLK(约为10K)，并将ACLK通过P1.0口输出
#include<msp430f6638.h>
void main(void)
{WDTCTL = WDTPW + WDTHOLD;          //关看门狗
UCSCTL4 |= SELA_1;                        //将ACLK时钟源配置为VLO；
P1DIR |= BIT0;
P1SEL |= BIT0;                            //将ACLK通过P1.0输出
__bis_SR_register(LPM3_bits);//进入LPM3，SMCLK和MCLK停止，ACLK活动}
设ACLK = XT1 = 32768Hz，并通过P1.0输出。
#include <msp430f6638.h>
void main(void)
{WDTCTL = WDTPW + WDTHOLD;        // Stop watchdog timer
  P1DIR |= BIT0;                            // ACLK set out to pin
  P1SEL |= BIT0;
  P5SEL |= BIT4+BIT5;                      // Select XT1
while(BAKCTL & LOCKIO)            // Unlock XT1 pins for operation
    BAKCTL &= ~(LOCKIO);
  UCSCTL6 &= ~(XT1OFF);                    // XT1 On
  UCSCTL6 |= XCAP_3;                        // Internal load cap
                                      // Loop until XT1 fault flag is cleared
  do
  {UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
  SFRIFG1 &= ~OFIFG;                      // Clear fault flags
  }while (SFRIFG1&OFIFG);                    // Test oscillator fault flag
  UCSCTL6 &= ~(XT1DRIVE_3);              // reduce drive strength
  UCSCTL4 |= SELA_0;                        // ACLK = LFTX1 (by default)
  __bis_SR_register(LPM3_bits);            // Enter LPM3
}
设ACLK = XT1 = 32768Hz，令SMCLK = XT2CLK，MCLK = DCO(默认) = 32 x ACLK = 1048576Hz，ACLK和SMCLK分别通过P1.0和P3.4输出。
#include <msp430f6638.h>
void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                // Stop WDT
  P1DIR |= BIT0;                            // ACLK set out to pins
  P1SEL |= BIT0;
  P3DIR |= BIT4;                            // SMCLK set out to pins
  P3SEL |= BIT4;
  while(BAKCTL & LOCKIO)                    // Unlock XT1 pins for operation
    BAKCTL &= ~(LOCKIO);
  P7SEL |= BIT2+BIT3;                      // Port select XT2
  UCSCTL6 &= ~XT2OFF;                      // Set XT2 On
  UCSCTL6 &= ~(XT1OFF);                    // XT1 On
  UCSCTL6 |= XCAP_3;                        // Internal load cap
  do
  {UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
  SFRIFG1 &= ~OFIFG;                      // Clear fault flags
  }while (SFRIFG1&OFIFG);                  // Test oscillator fault flag
  UCSCTL6 &= ~XT2DRIVE0;                  // Decrease XT2 Drive according to
                                            // expected frequency
  UCSCTL4 |= SELA_0 + SELS_5;      // Select SMCLK, ACLK source andDCO source
  while(1);                                // Loop in place
}
设ACLK = TACLK = LFXT1 = 32768, MCLK = SMCLK = DCOCLK = 32×ACLK = 1.048576Mhz，利用Timer_A输出周期为512 /32768 = 15.625ms、占空比分别为75%和25
%的PWM矩形波：
#include <msp430f6638.h>
void main(void)
{WDTCTL = WDTPW + WDTHOLD;                // Stop WDT
while(BAKCTL & LOCKIO)                       
BAKCTL &= ~(LOCKIO); // Unlock XT1 pins for operation
UCSCTL6 &= ~(XT1OFF);                    // XT1 On
UCSCTL6 |= XCAP_3;                        // Internal load cap
// Loop until XT1 fault flag is cleared

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