// D2A.C
//
// MCP4921 Diver
// RC0:  CS
// RC3:  CLK
// RC5:  DATA

//Global Variables
const unsigned char MSG0[21] = "D/A.C            "; 
const unsigned char MSG1[21] = "Square Wave      "; 
const unsigned int TABLE[16] = {2204, 2336, 2425, 2456, 2425, 2336, 2204, 2047, 1890, 1758, 1669, 1638, 1669, 1758, 1890, 2047};



// Subroutine Declarationsb
#include <pic18.h>

// Subroutines
#include        "lcd_portd.c"
  
void D2A(unsigned int X)
{
   unsigned char i;
   TRISC0 = 0;
   TRISC3 = 0;
   TRISC5 = 0;

// Add 0011 to the first four bits to set up the D/A
   X = X & 0x0FFF;
   X = X + 0x3000;
   RC0 = 1;
   RC3 = 1;

// CS goes low to select the D/A chip
   RC0 = 0;

// Send out 16 bits of data
   for (i=0; i<16; i++) {
      if (X & 0x8000) RC5 = 1; else RC5 = 0;
      RC3 = 0;
      X = X << 1;
      RC3 = 1;
      }

// CS goes high to terminate the communicaitons
   RC0 = 1;
      }
         

// Main Routine

void main(void)
{
   unsigned int i, j;
   int x, y, dx;

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

// Turn on the LCD
   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]); 


// Square Wave
/*
   while(1) {
      D2A(1638);
      for(i=1; i<3100; i++);
      D2A(2457);
      for(i=0; i<3100; i++);
      }
*/

// Sawtooth Wave
/*
   x = 1638;
   while(1) {
      D2A(x);
      x = x + 10;
      if(x > 2457) x = 1638;
      for(i=0; i<100; i++);
      }
*/
// Triangle Wave
/*
   x = 1638;
   dx = +10;
   while(1) {
      D2A(x);
      x = x + dx;
      if(x > 2457) dx = -10;
      if(x < 1638) dx = +10;
      for(i=0; i<100; i++);
      }
*/
//Parabolic Sine Wave
/*
   x = 0;
   dx = 0;
   while(1) {
      x = (x + 1) % 64;
      if(x == 0) dx = dx ^ 1;
      if(dx) y = 2048 + (2 * x * (64-x))/5;
      else y = 2048 - (2 * x * (64-x))/5;
      D2A(y);
      for(i=0; i<100; i++);
      }   
*/

// Look Up Table
   while(1) {
      i = (i + 1) % 16;
      D2A(TABLE[i]);
      for(j=0; j<177; j++);
      }

   }