请问PIT的用法

jchen5471

/现象B灯闪动,周期是INTVERAL*(0.01)ms,可用来记时.
//demo by whut_wj



#include <hidef.h>      /* common defines and macros */
#include <MC9S12XS128.h>     /* derivative information */
#pragma LINK_INFO DERIVATIVE "mc9s12xs128"

#define  INTVERAL 10000
void SetBusClock(void)
{   
    CLKSEL=0X00;      //disengage PLL to system
    PLLCTL_PLLON=1;   //turn on PLL
    SYNR=2;         
    REFDV=1;          //pllclock=2*osc*(1+SYNR)/(1+REFDV)=48MHz;
    _asm(nop);        //BUS CLOCK=24M
    _asm(nop);
    while(!(CRGFLG_LOCK==1));   //when pll is steady ,then use it;
    CLKSEL_PLLSEL =1;          //engage PLL to system;
}

void Dly_ms(int ms)   //24M时为1ms
{
   int i,j;
   for(i=0;i<ms;i++)
     for(j=0;j<0x7ff;j++);   
}

void PitInit(void)
{   

   PITCFLMT_PITE=0;       //disable PIT
   PITCE_PCE0=1;          //enable timer channel 0
   PITMTLD0=240-1;        //time base  240 clock cycles ,it's 0.1M Hz
   PITMUX=0X00;           // ch0 connected to micro timer 0
   PITLD0=INTVERAL-1;     //INTVERAL micro time bases  
   PITINTE_PINTE0=1;      //enable interupt channel 0
   PITCFLMT_PITE=1;       //enable PIT
   
                          //PITCNT0,类似于自由记数器,只不过一直是递减,TCNT是一直递增
}   

void main(void)
{

   EnableInterrupts;
   SetBusClock();
   PitInit();
   DDRB=0xff;

    for(;;)
    {

    }  
}


#pragma CODE_SEG __NEAR_SEG NON_BANKED
void interrupt 66 PIT0Interrupt(void)
{  
    PORTB^=0xff;
           PITTF_PTF0=1;
}

该程序是定时1s，可是做出来后效果却不是为什么

fi2005

你的定时时间是0.1S

jiangjie1229

24M/240=0.1MHZ  0.1M/10000=10HZ 即0.1s