Develop a realtime interrupt RTI driven change of LED light

Develop a real-time interrupt (RTI) driven change of LED light pattern display on the Dragon 12-Plus demo board. You need to write a C program to light up one LED at a time starting from the one driven by PORT B pin 7 till the one driven by PORT B pin 0 and then reverse the order of LED lighting. Repeat this operation forever. Each LED should be lighted for about 500 ms assuming that the HCS12 uses an 8-MHz crystal oscillator to generate a system clock.

Solution

void INTERRUPT timer6(void) {

      TFLG1 &= 0x40; // Next interrupt in 500ms
       TC6 += TB500MS;

        __asm__ __volatile__ (\" cli \");          /* Enable interrupts */

       select = (select+1) & 3;                       // Go to next digit

        PORTB = 0; // While we change, at least, we want display off

            if (ledFraction + ADR00H > 255) {              // display

             PTP = (PTP & 0xf0) | dspmap[select];

              if ((PTH & PB_MASK & ~ALARM_SW) == 0)          {        // Display Alarm Value

                      PORTB = segm_ptrn[dispa[select]] | dispadp[select];

                  } else { // Display current value

                    PORTB = segm_ptrn[dispt[select]] | disptdp[select];

                  }

             }

          if (select==0) ledFraction += ADR00H; // Save updated fraction

}