求助：5310单片机的晶振调试问题

1万 · 2012-9-19 12:42

原代码：
WDTCTL = WDTPW+WDTHOLD;                // Stop WDT

  PMAPPWD = 0x02D52;                      // Enable Write-access to modify port mapping registers
  P4MAP7 = PM_MCLK;
  PMAPPWD = 0;
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
                                          // 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);

  // 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

该代码调试是可以通过的，
但是，上述代码中其他寄存器的配置都不变
我仅改动  UCSCTL4 为
UCSCTL4 |= SELA_2+SELM0+SELM1+SELS0+SELS1;    // Set ACLK = REFO MCLK =SCLK=DCOCLK =12MHz

就通过不了，一直在
do
  {
UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
                                          // Clear XT2,XT1,DCO fault flags
SFRIFG1 &= ~OFIFG;                   // Clear fault flags
  }while (SFRIFG1&OFIFG);                // Test oscillator fault flag
循环中出不来，想问下大虾门是何原因？