/* Digital Voltmeter and
 3-wire Serial LCD using 74HC595
 Rajendra Bhatt, Oct 3, 2010
*/

sbit Data_Pin at GP5_bit;
sbit Clk_Pin at GP1_bit;
sbit Enable_Pin at GP2_bit;

// Always mention this definition statement
unsigned short Low_Nibble, High_Nibble, p, q,  Mask, N,t, RS, Flag, temp;

void Delay_50ms(){
 Delay_ms(50);
}

void Write_LCD_Nibble(unsigned short N){
 Enable_Pin = 0;
 // ****** Write RS *********
 Clk_Pin = 0;
 Data_Pin = RS;
 Clk_Pin = 1;
 Clk_Pin = 0;
 // ****** End RS Write

 // Shift in 4 bits
 Mask = 8;
  for (t=0; t<4; t++){
   Flag = N & Mask;
   if(Flag==0) Data_Pin = 0;
   else Data_Pin = 1;
   Clk_Pin = 1;
   Clk_Pin = 0;
   Mask = Mask >> 1;
  }
  // One more clock because SC and ST clks are tied
  Clk_Pin = 1;
  Clk_Pin = 0;
  Data_Pin = 0;
  Enable_Pin = 1;
  Enable_Pin = 0;
}
// ******* Write Nibble Ends

 void Write_LCD_Data(unsigned short D){
 RS = 1; // It is Data, not command
 Low_Nibble = D & 15;
 High_Nibble = D/16;
 Write_LCD_Nibble(High_Nibble);
 Write_LCD_Nibble(Low_Nibble);
 }

void Write_LCD_Cmd(unsigned short C){
 RS = 0; // It is command, not data
 Low_Nibble = C & 15;
 High_Nibble = C/16;
 Write_LCD_Nibble(High_Nibble);
 Write_LCD_Nibble(Low_Nibble);
}

void Initialize_LCD(){
 Delay_50ms();
 Write_LCD_Cmd(0x20); // Wake-Up Sequence
 Delay_50ms();
 Write_LCD_Cmd(0x20);
 Delay_50ms();
 Write_LCD_Cmd(0x20);
 Delay_50ms();
 Write_LCD_Cmd(0x28); // 4-bits, 2 lines, 5x7 font
 Delay_50ms();
 Write_LCD_Cmd(0x0C); // Display ON, No cursors
 Delay_50ms();
 Write_LCD_Cmd(0x06); // Entry mode- Auto-increment, No Display shifting
 Delay_50ms();
 Write_LCD_Cmd(0x01);
 Delay_50ms();
}

void Position_LCD(unsigned short x, unsigned short y){
 temp = 127 + y;
 if (x == 2) temp = temp + 64;
 Write_LCD_Cmd(temp);
}

void Write_LCD_Text(char *StrData){
 q = strlen(StrData);
 for (p = 0; p < q; p++){
  temp = StrData[p];
  Write_LCD_Data(temp);
 }

}

char Message1[] = "DVM Project";
unsigned int ADC_Value, DisplayVolt;
char *volt = "00.00";

void main() {
CMCON0 = 7;  // Disable Comparators
TRISIO = 0b00001001;  // All Outputs, except GP0 and GP3
ANSEL = 0x01; // GP0 analog i/p

Initialize_LCD();
Position_LCD(1,3);
Write_LCD_Text(Message1);
Position_LCD(2,10);
Write_LCD_Data('V');

do {

 ADC_Value = ADC_Read(0);
 DisplayVolt = ADC_Value * 2;

 volt[0] = DisplayVolt/1000 + 48;
 volt[1] = (DisplayVolt/100)%10 + 48;
 volt[3] = (DisplayVolt/10)%10 + 48;
 volt[4] = DisplayVolt%10 + 48;
 Position_LCD(2,4);
 Write_LCD_Text(volt);
 delay_ms(100);
} while(1);

}