Stop Watch   Stop Watch function via RTCC & interrupts ///////////////////////////////////////////////////////////////////////// //// EX_STWT.C //// //// //// //// This program uses the RTCC (timer0) and interrupts to keep a //// //// real time seconds counter. A simple stop watch function is //// //// then implemented. //// //// //// //// (C) Copyright 1996,1997 Custom Computer Services //// //// //// ///////////////////////////////////////////////////////////////////////// #include <16F84.H> #fuses XT,NOWDT,NOPROTECT #use delay(clock=4000000) #use rs232(baud=9600, xmit=PIN_A3, rcv=PIN_A2) #define INTS_PER_SECOND 76 // (20000000/(4*256*256)) byte seconds; // A running seconds counter byte int_count; // Number of interrupts left before a second has elapsed #int_rtcc // This function is called every time clock_isr() { // the RTCC (timer0) overflows (255->0). // For this program this is apx 76 times if(--int_count==0) { // per second. ++seconds; int_count=INTS_PER_SECOND; } } main() { byte start; int_count=INTS_PER_SECOND; set_rtcc(0); setup_counters( RTCC_INTERNAL, RTCC_DIV_256); enable_interrupts(RTCC_ZERO); enable_interrupts(GLOBAL); do { printf("Press any key to begin.\n\r"); getc(); start=seconds; printf("Press any key to stop.\n\r"); getc(); printf("%u seconds.\n\r",seconds-start); } while (TRUE); }

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