#define ECHO PORTB.F0
#define TRIG PORTB.F1

// LCD module connections
 sbit LCD_RS at RB2_bit;
 sbit LCD_EN at RB3_bit;
 sbit LCD_D4 at RB4_bit;
 sbit LCD_D5 at RB5_bit;
 sbit LCD_D6 at RB6_bit;
 sbit LCD_D7 at RB7_bit;

sbit LCD_RS_Direction at TRISB2_bit;
sbit LCD_EN_Direction at TRISB3_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections


unsigned int Time;
unsigned int Distance;
char txt[14];

void interrupt()
{
if (INTCON.INTF)    // IF RB0 is occured
                  {
                  if ( ECHO == 1) {
                                   INTCON.INTF = 0;  // make the interrupt to 0 again
                                   OPTION_REG.INTEDG=0; // interrupts activated at falling edge
                                   T1CON.TMR1ON =1;       //enable timer
                                  }

                  if ( ECHO == 0) {
                                   INTCON.INTF = 0;  // make the interrupt to 0 again
                                   OPTION_REG.INTEDG=1; // interrupts activated at rising edge
                                   T1CON.TMR1ON =0;       //disable timer
                                   Time = (TMR1H<<8)+(TMR1L); // to read the value of the timer ( shift left and add )
                                   TMR1L=TMR1H=0;
                                  }
                  }

}

void main()
{

OPTION_REG.INTEDG=1;
delay_ms(500);
Lcd_Init();                 //Initialize LCD
delay_ms(500);
Lcd_Cmd(_LCD_CLEAR);        // Clear display
Lcd_Cmd(_LCD_CURSOR_OFF);   // Cursor off
Lcd_Out(1,2,"((--Distance--))");
TRISA = 0;
TRISB.F0=1;
TRISB.F1=0;
INTCON = 0b11010000;         //  enable global interrupt, preiferal is enables , and RB0 externl interupt is enabled
T1CON =  0b00000001;         // set prescaler to 1:1 and enable timer 1.


while(1)
{
TRIG =0;
Delay_us(1000);
TRIG = 1;
delay_us(20);
TRIG = 0;
Distance = Time * 1.716 * 0.927856;

inttostr(Time,txt);  //
lcd_out(2,3,txt) ;
lcd_out(2,11,"cm") ;


}


}

 Time = TMR1H;
                                   Time = (Time<<8)
                                   Time = Time +(TMR1L); // to read the value of the timer ( shift left and add )

// LCD module connections
 sbit LCD_RS at RB2_bit;
 sbit LCD_EN at RB3_bit;
 sbit LCD_D4 at RB4_bit;
 sbit LCD_D5 at RB5_bit;
 sbit LCD_D6 at RB6_bit;
 sbit LCD_D7 at RB7_bit;

sbit LCD_RS_Direction at TRISB2_bit;
sbit LCD_EN_Direction at TRISB3_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections

char txt[14];
#define TRIG PORTA.F5
#define ECHO PORTA.F4


int distance;
int test;

//main function
void main() {
  delay_ms(500);
  Lcd_Init();
  delay_ms(500);                                                                    //Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);                                                              // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);                                                          // Cursor off
  Lcd_Out(1,2,"( Distance )");
  TRISA.F5=0;                                                                   //port b.6 as out port
  TRISA.F4=1;                                                                   //portb.7 as input from the module

T1CON = 0b00000000;                                                           // config timer refer page 79 of datasheet
  INTCON =0b11000000;
  PIE1 =0x01;
  /*
    >>here we use prescalor of 8, and the internal clock ,precisly fosc/4
    so one increment will be (let the crstal you use is 8mhz)
    8m/(4*8) ie 250000hz or 4us
    >>distance traveled by sound is about 343 m/s (in air at 20degrees)
    for 30 uS the sound will travel about 1 c.m.
    each 1cm ( soundwave ) = 30us
    (we have a precision of 1c.m if you need to change by calculating the number
    of increment for the patricular length and then changing the calculation
    accordingly
    >>the sound is reflected back, so we have to divide the value from timer
    with 2
  */