Pulse Width Measuring

#include <c8051f340.h>

bit FLAG;

unsigned char CAPTURE; 

unsigned char A;

unsigned char C;    

unsigned char Pulse_Width;

void port_init (void);

void pca_init (void);

 void main (void)

{

   port_init ();             //

   pca_init ();     

   PCA0MD &= ~0x40;                // Disable Watchdog Timer

// PCA Timer INIT:

 PCA0MD = 0x00;                // Input to timer 4 1/12 X Fosc

 TH0 = 0x00;      // High Byte

 TL0 = 0x00;       //Low Byte

 IE = 1;

 //EIE1=1;              // Enable External interrupt 1

 EA = 1;               // Enable all interrupts

 ET0= 1;              // Turn PCA timer 0 on

 CR=1;

 while (1){  }            // wait of interrupt

               // 

}

void pca_init (void)

{

    PCA0CN    = 0x40;        //

    PCA0CPM0  = 0x21;        //Capture positive edge first for measuring pulse width

    PCA0MD    = 0x00;             //

    FLAG=0;

}

void port_init (void)

{  P0SKIP = 0xff;              //

   P1SKIP = 0x03;             //

   P1MDOUT |= 0x04;           //

}

void Int_0_ISR(void) interrupt 0

{

  CCF0 =0;          // Clear Module 0's event flag

  if (FLAG==0)         // Check if this is the first

  {      

       // capture or second:

   // FIRST CAPTURE:

   CAPTURE   = PCA0CPL0;       // Save 16-bit capture value

   PCA0CPH0  = CAPTURE+1; 

   PCA0CPM0 = 0x11;          // Change module to now capture

                             // falling edges

   FLAG = 1;                 //1st capture complete 

   }

   else // SECOND CAPTURE:

   {

     Pulse_Width = CAPTURE - PCA0CPL0;

     A = Pulse_Width+1;

     C  = PCA0CPH0 - CAPTURE;

     A = C;

     PCA0CPM0 = 0x21;         //Optional: needed if user wants to

     FLAG = 0;              //measure next pulse width

   }

}