Touch Screen Interfacing with PIC16F877A

#include <18f4520.h>
#use delay(clock=40000000)
#use rs232(baud=9600, UART1)      // hardware UART; uses  RC6/TX and RC7/RX
#include "flex_lcd.c"             //must include in order to output to LCD

int j;
int16 x_pos, y_pos;

void get_screen_pos(int16& x_pos, int16& y_pos);

void main()
{

   lcd_init();  // Always call this first.

   //command Format Tablet: "<SOH>FT<CR>" sent to touchscreen via RC6/TX pin
   putc(0x01);
   putc(0x46);
   putc(0x54);
   putc(0x0D);

   while (TRUE)
   {
      //get the finger position relative to the touchscreen in 16-bit int format
      get_screen_pos(x_pos, y_pos);

      printf(lcd_putc,"\fX: %Lu\n",x_pos); //output "X: <x_pos>" to first line of LCD
      printf(lcd_putc,"Y: %Lu",y_pos);     //output "Y: <y_pos>" to second line of LCD
   }
}

//Function adapted from Nick Marchuk's IR touchscreen code
void get_screen_pos(int16& x_pos, int16& y_pos)
{
   int i, gotD8, j;
   int touchscreen_rcx[20];
   int pos[5];
   int16 high16, low16, xtotal16, ytotal16;
   int temp4, total8;
   high16 = 0;
   low16 = 0;
   xtotal16 = 0;
   ytotal16 = 0;
   temp4 = 0;
   total8 = 0;

   //get 10 bytes from the touchscreen (each touch signal is 10 bytes)
   for (i=1;i<=10;++i)
   {
      touchscreen_rcx[i] = getc();
   }

   //find the first instance of 0xD8 (start of each signal)
   gotD8 = 0;
   j = 1;
   while(gotD8==0)
   {
      if((touchscreen_rcx[j] == 0xD8))
      {
         gotD8 = 1; //j is the location of 0xD8
      }
      else
      {
         j = j+1;
      }

      if(j==9)
      {
         gotD8 = 1; //didnt find it, dont loop forever
      }
   }

   pos[1] = touchscreen_rcx[j+1]; //xlow, bits: 0 X6 X5 X4 X3 X2 X1 X0 (see touchscreen datasheet for FT response))
   pos[2] = touchscreen_rcx[j+2]; //xhigh, bits: 0 X13 X12 X11 X10 X9 X8 X7
   pos[3] = touchscreen_rcx[j+3]; //ylow, bits: 0 Y6 Y5 Y4 Y3 Y2 Y1 Y0
   pos[4] = touchscreen_rcx[j+4]; //yhigh, bits: 0 Y13 Y12 Y11 Y10 Y9 Y8 Y7

   //make the x
   temp4 = pos[2];
   high16 = temp4; //make high16= 0000 0000 0X13X12X11 X10X9X8X7
   low16 = pos[1]; //make low16= 0000 0000 0X6X5X4 X3X2X1X0

   xtotal16 = low16|(high16<<7); //OR 00X13X12 X11X10X9X8 X7000 0000 with 0000 0000 0X6X5X4 X3X2X1X0
   x_pos = xtotal16; //x_pos=00X13X12 X11X10X9X8 X7X6X5X4 X3X2X1X0

   //make the y
   temp4 = pos[4];
   high16 = temp4; //make high16= 0000 0000 0Y13Y12Y11 Y10Y9Y8Y7
   low16 = pos[3]; //make low16= 0000 0000 0Y6Y5Y4 Y3Y2Y1Y0

   ytotal16 = low16|(high16<<7); //OR 00Y13Y12 Y11Y10Y9Y8 Y7000 0000 with 0000 0000 0Y6Y5Y4 Y3Y2Y1Y0
   y_pos = ytotal16;             //x_pos=00Y13Y12 Y11Y10Y9Y8 Y7Y6Y5Y4 Y3Y2Y1Y0
}