//******************************************************************************* //程 序 名：高精度時鐘 //設 計 者：石魚WLEEN //設計說明：設置TMR0預分頻系數為16，一次計數中斷溢出時間為4096us(0x1000) // 每次TMR0中斷服務中對時間累計變量microsecond加上4096 // 程序主循環中不停地查詢變量microsecond，看是否超過50ms,如果時間超過 // 50ms,則microsecond=microsecond-50000，同時50ms計數器ms50加1 // 基于50ms計數器的累加值，更新秒，分和小時值 // 雖然每一個50ms的變化時間略有偏差，但所有偏差值都保留在microsecond // 中,并得到累計修正，所以長時間跨度計時精確 //******************************************************************************* #include

//*******************//variable define//**********************************

long int microsecond; //microsecond accumulative unit int ms50; //50ms counter int second; //second counter int minute; //minute counter int hour; //hour counter

main() {

//*******************//initialize//************************************** T0CS=0; //timer0 work at timer mode T0IF=0; //clear timer0 flag PSA=0; PS2=1; PS1=0; PS0=0; //psa=0,ps2:ps0=100,1:16 prescale value T0IE=1; //timer0 overflow interrupt enable GIE=1; // global interrupt enable

//*******************//main loop//************************************** while(1) { CLRWDT(); //clear the watchdog T0IE=0; //temporarily forbid the timer0 to interrupt //to keep the value of microsecond

microsecond-=50000; if(microsecond>=50000) //deal with microsecond>=50000 { ms50=+1; //50ms counter increase 1 if(ms50!=20) T0IE=1; //the time is not one second, resume t0ie ms50=0; //the time is one second,clear ms50 second++; //second counter if(second!=60) T0IE=1; //the time is not one minute, resume t0ie second=0; //the time is one minute,clear second minute++; //minute counter if(minute!=60) T0IE=1; //the time is not one hour, resume t0ie minute=0; //the time is one hour,clear minute hour++; //hour counter if(hour!=24) T0IE=1; //the time is not 24h, resume t0ie hour=0; //the time is 24 hour,clear hour } else microsecond+=50000; T0IE=1; //resume t0ie } }

void interrupt timer(void) { microsecond+=4096; }