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。
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