设置DCO范围为什么会不一样

1万 · 2016-3-19 20:41

我在用到MSP430F6733单片机时看到有
UCSCTL3 |= SELREF_2;                // Set DCO FLL reference = REFO
UCSCTL4 |= SELA_2;                   // Set ACLK = REFO

__bis_SR_register(SCG0);             // Disable the FLL control loop
UCSCTL0 = 0x0000;                   // Set lowest possible DCOx, MODx
UCSCTL1 = DCORSEL_5;                // Select DCO range 16MHz operation
UCSCTL2 = FLLD_1 | 243;             // Set DCO Multiplier for 8MHz
  然后还有

// Setup LFXT1
UCSCTL6 &= ~(XT1OFF);                // XT1 On
UCSCTL6 |= XCAP_3;                   // Internal load cap

// Loop until XT1 fault flag is cleared
do
{
      UCSCTL7 &= ~XT1LFOFFG;          // Clear XT1 fault flags
} while (UCSCTL7 & XT1LFOFFG);       // Test XT1 fault flag

// Initialize DCO to 2.45MHz
__bis_SR_register(SCG0);             // Disable the FLL control loop
UCSCTL0 = 0x0000;                   // Set lowest possible DCOx, MODx
UCSCTL1 = DCORSEL_5;                // Set RSELx for DCO = 4.9 MHz
UCSCTL2 = FLLD_1 | 243;                // Set DCO Multiplier for 2.45MHz
这两个区别在于选择DCO的时钟源不同，那 UCSCTL1 = DCORSEL_5;                设置DCO范围为什么会不一样，