// Tach.C
// Measure the period of a square wave on RC0
// Interrupts
// Timer0:  Time accurate to 100ns
// Timer1:  Interrupt on rising edge of RC0
// Timer2:  Output a 1kHz test signal on RC1

// Global Variables

const unsigned char MSG0[21] = "Tach                "; 
const unsigned char MSG1[21] = "sec                 ";     

unsigned long int TIME;
unsigned long int T2, T1;
unsigned long int PERIOD;


// Subroutine Declarations
#include <pic18.h>

// Subroutines
#include        "lcd_portd.c"

// Interrupt Service Routine
void interrupt IntServe(void)
{
   if (TMR0IF) {
      TIME = TIME + 0x10000;
      TMR0IF = 0;
      }
   if (TMR1IF) {
      TMR1 = -1;
      T2 = T1;
      T1 = TIME + TMR0;
      PERIOD = T1 - T2;
      TMR1IF = 0;
      }
   if (TMR2IF) {
      RC1 = !RC1;
      TMR2IF = 0;
      }
   }
 
          
// Main Routine

void main(void)
{
   unsigned char i;
   unsigned int Hz;

   TRISA = 0;
   TRISB = 0xFF;
   TRISC = 0;
   TRISD = 0;
   TRISE = 0;
   ADCON1 = 0x0F;

   LCD_Init();                  // initialize the LCD

   LCD_Move(0,0);  for (i=0; i<20; i++) LCD_Write(MSG0[i]);
   LCD_Move(1,0);  for (i=0; i<20; i++) LCD_Write(MSG1[i]);

   Wait_ms(100);

// set up Timer0 for PS = 1
   T0CS = 0;
   T0CON = 0x88;
   TMR0ON = 1;
   TMR0IE = 1;
   TMR0IP = 1;
   PEIE = 1;
// set up Timer1 for PS = 1, input = RC0
   T1CON = 0x81;
   TMR1ON = 1;
   TMR1IE = 1;
   TMR1IP = 1;
   PEIE = 1;
   TMR1CS = 1;
   TRISC0 = 1;
// set up Timer2 for 0.5ms
   T2CON = 0x4D;
   PR2   = 124;
   TMR2ON = 1;
   TMR2IE = 1;
   TMR2IP = 1;
   PEIE = 1;

// turn on all interrupts
   GIE = 1;

   TIME = 0;

   while(1) {
  
      LCD_Move(0,5);  LCD_Out(TIME + TMR1, 9, 7);
      LCD_Move(1,5);  LCD_Out(PERIOD, 9, 7);
        
      }      


   }