// Use the Timer Interrupt to implemenet a 4-digits 7-Segment Clock, only minutes and seconds are shown
// Use Common Anode 7-Segs, LED segment On when LOW, Digits On when LOW/HIGH (comment out the appropriate statements)
// The statements within the Timer Interrupt also consume CPU times, therefore, it cannot be used to
// calculate time and do 1~50ms 7-Seg refreshing at the same time without flickering.


int Dig[10];  // digits 0..9
int buf[4];   // display buffer
int nxt;      // index to buf[]


main()
{
   int   m, s;
 

//   pinhigh(8); pinhigh(9); pinhigh(10); pinhigh(11);       // switch all Digits OFF, for Digits On when LOW
   pinlow(8); pinlow(9); pinlow(10); pinlow(11);           // switch all Digits OFF, for Digits On when HIGH

   init_digits();
   buf[0] = Dig[m/10];
   buf[1] = Dig[m%10];
   buf[2] = Dig[s/10];
   buf[3] = Dig[s%10];

   loop {
     delay(100);  // need to tune here for accuracy!
     s++; buf[2]=Dig[s/10]; buf[3]=Dig[s%10];
     if(s >= 60) { s=0; m++; buf[2]=Dig[0]; buf[0]=Dig[m/10]; buf[1]=Dig[m%10]; if(m >= 60) { m=0; buf[0]=Dig[0]; }}
   }
}

time0() timer 1
{
   pinlow(8+nxt++);                // switch selected Digit Off, LOW
//   pinhigh(8+nxt++);               // switch selected Digit Off, HIGH
   nxt %= 4;
   writeb(0, buf[nxt], 0);
//   pinlow(8+nxt);                  // switch selected Digit On, LOW
   pinhigh(8+nxt);                 // switch selected Digit On, HIGH
}

init_digits()
{
   Dig[0] = 0xC0; Dig[1] = 0xF9; Dig[2] = 0xA4; Dig[3] = 0xB0; Dig[4] = 0x99; 
   Dig[5] = 0x92; Dig[6] = 0x82; Dig[7] = 0xF8; Dig[8] = 0x80; Dig[9] = 0x90;
}