Freescale MC9S12G128 PLL,OSC

PLL OSC简述：

S12CPMU Block Diagram:

S12CPMU Synthesizer Register(CPMUSYNR)

PLL相关主要寄存器：
CPMUPROT:时钟配置寄存器保护
Clock Configuration Registers Protection Bit — This bit protects the clock configuration registers from
accidental overwrite (see list of affected registers above):
Writing 0x26 to the CPMUPROT register clears the PROT bit, other write accesses set the PROT bit.
0 Protection of clock configuration registers is disabled.
1 Protection of clock configuration registers is enabled.
0x26:将0x26写入CPMUPROT寄存器清除PROT位，其他写入访问设置PROT位
0:关闭保护
1:使能保护

S12CPMU PLL Control Register (CPMUPLL)
0x003A
Read:Anytime
Write: Anytime if PROT=0 (CPMUPROT register) and PLLSEL=1 (CPMUCLKS register). Else write has
no effect.
CPMUPLL[5:4] FM1, FM0
0x00:关闭FM
0x10: ±1%
0x20:±2%
0x30:±3%

FM1	FM0	FM Amplitude/Fvco Variation
0	0	FM off
0	1	±1%
1	0	±2%
1	1	±3%

CPMUSYNR:
CPMUREFDIV:REFDIV基准分频器配置
CPMUPOSTDIV:POST分配配置

PLL设置示例：

#include <hidef.h>      /* common defines and macros */
#include "derivative.h"      /* derivative-specific definitions */

#define D_

#define LED PORTA
#define LED_DIR DDRA


void delay(void) {
    
    
  unsigned int i;
  for(i=0; i<60000; i++) {
    
    
    _asm(nop);
    _asm(nop);
    _asm(nop);
    _asm(nop);
    _asm(nop);
    _asm(nop);
  }
}


void pll_init(void) {
    
    
  CPMUPROT = 0x26;              //保护时钟配置寄存器
  
  CPMUCLKS_PSTP = 0;            //禁用PLL
  CPMUCLKS_PLLSEL = 1;          //选择PLL作为系统时钟源
  
  CPMUOSC_OSCE = 1;             //外部晶振使能
  while(CPMUOSC_OSCPINS_EN==0); //等待外部晶振使能
  
  /* CPMUSYNR     VCOFRQ［7:6］， SYNDIV［5:0］ */
  /* CPMUREFDIV   REFFRQ［7:6］， REFDIV［3:0］ */
  /* CPMUPOSTDIV  POSTDIV [0] = 0,   FPLL = FVCO   */
  
  #if 0
  //fVOC= 2*fOSC*(SYNDIV + 1)/(REFDIV + 1) 
  CPMUSYNR = 0x07;                                                  
  CPMUREFDIV = 0x0F; // 16M     
  //CPMUREFDIV = 0x07; // 32M       
  //CPMUREFDIV = 0x03; // 64M       
  #endif
  
  #if 1
  //fVOC配置 fVOC = 2*fREF*(SYNDIV +1)
  //CPMUSYNR = 0x45; // 48M
  //CPMUSYNR = 0x44; // 40M
  //CPMUSYNR = 0x43; // 32M
  //CPMUSYNR = 0x42; // 24M
  CPMUSYNR = 0x01; // 16M
  CPMUREFDIV = 0x81;//REFDIV基准分频器配置
  #endif
    
  CPMUPOSTDIV = 0x00;           // PLL CLOCK = VCO CLOCK / (POSTDIV + 1) 
                              
  _asm(nop);
  _asm(nop);
  
  CPMUPLL=0x10;               //锁相环调频启用,用以减少噪音
    
  while(CPMUFLG_LOCK == 0);	  //等待PLL稳定 wait for VCO to stabilize
  
  	  
  CPMUPROT = 0x00;            //关闭保护时钟
  CPMUCLKS_PLLSEL = 1;        /* Switch clk to use PLL */
}


void led_init(void) {
    
    
  LED = 0xFF;
  LED_DIR = 0xFF;
}


void main(void) {
    
    
  /* put your own code here */
  
  DisableInterrupts;  // 关闭总中断

  pll_init();
  led_init();
  
	EnableInterrupts;   // 开启总中断


  for(;;) {
    
    
  
     delay();
     LED = 0x00;
     delay();
     LED = 0xFF;
     
    _FEED_COP(); /* feeds the dog */
  } /* loop forever */
  /* please make sure that you never leave main */
}