原创 MSP430F5510时钟模块

我给出一张截图，需要注意的我都标在上面了，图片需要放大观看的。

下面是TI提供的一个例程，我不多说，简单说几句。

//******************************************************************************
//   MSP430F550x Demo - Software Toggle P1.1 with 12MHz DCO
//
//   Description: Toggle P1.1 by xor'ing P1.1 inside of a software loop.
//   ACLK is rought out on pin P1.0, SMCLK is brought out on P2.2, and MCLK
//   is brought out on pin P4.7.
//   ACLK = REFO = 32kHz, MCLK = SMCLK = 12MHz
//
//                 MSP430F550x
//             -----------------
//         /||                 |
//          | |             P1.0|-->ACLK
//          --|RST          P4.7|-->MCLK
//            |             P2.2|-->SMCLK
//            |                 |
//            |             P1.1|-->Port Pin
//
//   D. Archbold
//   Texas Instruments Inc.
//   April 2009
//   Built with CCSv4 and IAR Embedded Workbench Version: 4.21
//******************************************************************************
#include

void SetVcoreUp (unsigned int level);

void main(void)
{
  volatile unsigned int i;

  WDTCTL = WDTPW+WDTHOLD;             // Stop WDT
  
  PMAPPWD = 0x02D52;                 // Enable Write-access to modify port mapping registers
  P4MAP7 = PM_MCLK;
  PMAPPWD = 0;                       // Disable Write-Access to modify port mapping registers  
  
  P1DIR |= BIT1;                            // P1.1 output
  
  P1DIR |= BIT0;                            // ACLK set out to pins
  P1SEL |= BIT0;                            
  P2DIR |= BIT2;                            // SMCLK set out to pins
  P2SEL |= BIT2;                            
  P4SEL |= BIT7;
  P4DIR |= BIT7;                            // MCLK set out to pins
  
  UCSCTL3 |= SELREF_2;                      // Set DCO FLL reference = REFO
  UCSCTL4 |= SELA_2;                        // Set ACLK = REFO

                                 // Increase Vcore setting to level1 to support fsystem=12MHz
                                 // NOTE: Change core voltage one level at a time..
  SetVcoreUp (0x01);

                                 // Initialize DCO to 12MHz  
  __bis_SR_register(SCG0);                  // Disable the FLL control loop
  UCSCTL0 = 0x0000;                         // Set lowest possible DCOx, MODx
  UCSCTL1 = DCORSEL_5;                      // Select DCO range 24MHz operation
  UCSCTL2 = FLLD_1 + 374;                   // Set DCO Multiplier for 12MHz
                                            // (N + 1) * FLLRef = Fdco
                                            // (374 + 1) * 32768 = 12MHz

      对照图片上面的公式，应该很清楚了。因为FLLD_1就是上面的D，它是1，所以就给省略了。
                                            // Set FLL Div = fDCOCLK/2
  __bic_SR_register(SCG0);                  // Enable the FLL control loop

  // Worst-case settling time for the DCO when the DCO range bits have been
  // changed is n x 32 x 32 x f_MCLK / f_FLL_reference. See UCS chapter in 5xx
  // UG for optimization.
  // 32 x 32 x 12 MHz / 32,768 Hz = 375000 = MCLK cycles for DCO to settle
  __delay_cycles(375000);这段话在MSP430F5510datasheet里面有说明的，自己可以找一下。
 
  // Loop until XT1,XT2 & DCO 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
 
  while(1)
  {
    P1OUT ^= BIT1;                          // Toggle P1.0
    __delay_cycles(600000);                 // Delay
  }
}

void SetVcoreUp (unsigned int level)
{
  // Open PMM registers for write
  PMMCTL0_H = PMMPW_H;              
  // Set SVS/SVM high side new level
  SVSMHCTL = SVSHE + SVSHRVL0 * level + SVMHE + SVSMHRRL0 * level;
  // Set SVM low side to new level
  SVSMLCTL = SVSLE + SVMLE + SVSMLRRL0 * level;
  // Wait till SVM is settled
  while ((PMMIFG & SVSMLDLYIFG) == 0);
  // Clear already set flags
  PMMIFG &= ~(SVMLVLRIFG + SVMLIFG);
  // Set VCore to new level
  PMMCTL0_L = PMMCOREV0 * level;
  // Wait till new level reached
  if ((PMMIFG & SVMLIFG))
    while ((PMMIFG & SVMLVLRIFG) == 0);
  // Set SVS/SVM low side to new level
  SVSMLCTL = SVSLE + SVSLRVL0 * level + SVMLE + SVSMLRRL0 * level;
  // Lock PMM registers for write access
  PMMCTL0_H = 0x00;
}

 

最后说明一下的，这里说起来，好像时钟模块很复杂，其实，我们实际使用的时候比较简单，比如XT1外接一个32.768K晶振，XT2外接一个12M晶振，然后ACLK=XT1，MCLK=SMCLK=XT2，就好了，这里说的，主要是说说DCO，和内部自己震荡源，比较特殊，一般不怎么用，除非你没有任何外接晶振，只能使用内部的振荡器。