#include <htc.h>
#include <sys.h>
#include <stdlib.h>

interrupt void isr(void);

unsigned char i, j, k, m, n, dat1, dat2, dat3, dat4;

interrupt void isr(void)
 {
  if(k==255)            //counters for timer overflow
   {
    if(m==255) n=n+1;
    m=m+1;
   } 
  k=k+1;
  INTCON=0b10100000;   // resets the TMR0 interupt flag
 } 

void main(void)
{
 RCSTA=0b10010000;    // enable serial port, enable continuous receive
 TXSTA=0b00100100;    // transmit enabled, asynchronous, mode high speed
 SPBRG=20;            // Set Baud Rate to 56K
 OPTION=0b00000000;   // Fastest timer rate
 INTCON=0b10100000;   // enables all interupts, enables the TMR0 interupt
 TRISB=0b00110000;    // port B bits 4 and 5 as input
 TRISD=0b00000000;    // all port D bits as output
 i=0;
 k=0;
 m=0;
 n=0;
 while(1)
  {
       PORTD = 0b11110000;  // turn LED on
    while ((PORTB & 0b00010000)==16)   // check if detector reads light
        {}                             // wait till light is off
      dat1=TMR0;              // get the time value
      dat2=k;
      dat3=m;
      dat4=n;      
      PORTD = 0b11010000;    // turn LED off
      while((PIR1 & 0b00010000)==0){};      // Do the serial transfer of ON time
      TXREG=dat4;
      for(i=1;i<3;i++) {}
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat3;
      for(i=1;i<3;i++) {}
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat2;
      for(i=1;i<3;i++) {}
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat1;

    while ((PORTB & 0b00010000) == 0)   // check if detector reads light
        {}                              // wait till light is on
      dat1=TMR0;                        // get the time value
      dat2=k;
      dat3=m;
      dat4=n; 
      while((PIR1 & 0b00010000)==0){};  // Do the serial transfer of OFF time
      TXREG=dat4;
      for(i=1;i<3;i++) {}       
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat3;
      for(i=1;i<3;i++) {}
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat2;
     for(i=1;i<3;i++) {}
      while((PIR1 & 0b00010000)==0){};
      TXREG=dat1;

   } 

}