1、背景：
许久未更新博客，最近由于项目需求，简单使用430做接口，但由于内部默认可使用1MHz的频率无法满足需求；
2、功能：
经查阅手册发现片子支持DCO倍频，频率可以高达16M，经验证满足需求；
3、前提：
需要外接32K晶振作为校正频率；
4、参阅代码如下：
#include <msp430.h>// 32KHz/8=4096Hz，由此计算倍频
#define DELTA_1MHZ 244 // 244 x 4096Hz = 999.4Hz#define DELTA_8MHZ 1953 // 1953 x 4096Hz = 7.99MHz
#define DELTA_12MHZ 2930 // 2930 x 4096Hz = 12.00MHz
#define DELTA_16MHZ 3906 // 3906 x 4096Hz = 15.99MHz
unsigned char CAL_DATA[8]; // Temp. storage for constants
volatile unsigned int i;
int j;
char *Flash_ptrA; // Segment A pointer
void Set_DCO(unsigned int Delta);
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
for (i = 0; i < 0xfffe; i++); // Delay for XTAL stabilization
P1OUT = 0x00; // Clear P1 output latches
P1SEL = 0x10; // P1.4 SMCLK output
P1DIR = 0x11; // P1.0,4 output
j = 0; // Reset pointer
Set_DCO(DELTA_16MHZ); // Set DCO and obtain constants
CAL_DATA[j++] = DCOCTL;
CAL_DATA[j++] = BCSCTL1;
Set_DCO(DELTA_12MHZ); // Set DCO and obtain constants
CAL_DATA[j++] = DCOCTL;
CAL_DATA[j++] = BCSCTL1;
Set_DCO(DELTA_8MHZ); // Set DCO and obtain constants
CAL_DATA[j++] = DCOCTL;
CAL_DATA[j++] = BCSCTL1;
Set_DCO(DELTA_1MHZ); // Set DCO and obtain constants
CAL_DATA[j++] = DCOCTL;
CAL_DATA[j++] = BCSCTL1;
Flash_ptrA = (char *)0x10C0; // Point to beginning of seg A
FCTL2 = FWKEY + FSSEL0 + FN1; // MCLK/3 for Flash Timing Generator
FCTL1 = FWKEY + ERASE; // Set Erase bit
FCTL3 = FWKEY + LOCKA; // Clear LOCK & LOCKA bits
*Flash_ptrA = 0x00; // Dummy write to erase Flash seg A
FCTL1 = FWKEY + WRT; // Set WRT bit for write operation
Flash_ptrA = (char *)0x10F8; // Point to beginning of cal consts
for (j = 0; j < 8; j++)
*Flash_ptrA++ = CAL_DATA[j]; // re-flash DCO calibration data
FCTL1 = FWKEY; // Clear WRT bit
FCTL3 = FWKEY + LOCKA + LOCK; // Set LOCK & LOCKA bit
while (1)
{
P1OUT ^= 0x01; // Toggle LED
for (i = 0; i < 0x4000; i++); // SW Delay
}
}
// 计算倍频
void Set_DCO(unsigned int Delta) // Set DCO to selected frequency
{
unsigned int Compare, Oldcapture = 0;
BCSCTL1 |= DIVA_3; // ACLK = LFXT1CLK/8
TACCTL0 = CM_1 + CCIS_1 + CAP; // CAP, ACLK
TACTL = TASSEL_2 + MC_2 + TACLR; // SMCLK, cont-mode, clear
while (1)
{
while (!(CCIFG & TACCTL0)); // Wait until capture occured
TACCTL0 &= ~CCIFG; // Capture occured, clear flag
Compare = TACCR0; // Get current captured SMCLK
Compare = Compare - Oldcapture; // SMCLK difference
Oldcapture = TACCR0; // Save current captured SMCLK
if (Delta == Compare)
break; // If equal, leave "while(1)"
else if (Delta < Compare)
{
DCOCTL--; // DCO is too fast, slow it down
if (DCOCTL == 0xFF) // Did DCO roll under?
if (BCSCTL1 & 0x0f)
BCSCTL1--; // Select lower RSEL
}
else
{
DCOCTL++; // DCO is too slow, speed it up
if (DCOCTL == 0x00) // Did DCO roll over?
if ((BCSCTL1 & 0x0f) != 0x0f)
BCSCTL1++; // Sel higher RSEL
}
}
TACCTL0 = 0; // Stop TACCR0
TACTL = 0; // Stop Timer_A
BCSCTL1 &= ~DIVA_3; // ACLK = LFXT1CLK
}