PIC16F877A EEPROM

/*---------------------------------------------/
    Name    : Mohd Syahri Fikri Bin Samusi

    EEPROM with ADC

    Date Modified: 22 March 2012
/---------------------------------------------*/

#include <htc.h>
#include <pic16f877a.h>
#include <stdio.h>
#define _XTAL_FREQ 20000000 // Set the oscillator frequency to 20MHz
#define neutral_zone 25 //0.5 Volts

void init_rs232( )
{
    BRGH = 1;
    SPBRG = 129;    // set baud rate: Fosc=20Mhz, BR=9600
    TX9  = 0;   // ninebits?1:0,,,8- or 9-bit transmission
    SYNC = 0;   // asynchronous
    SPEN = 1;   // enable serial port pins
    TXEN = 1;   // enable the transmitter & (automatically)TXIF=1
    CREN = 1;   // enable reception
    SREN = 0;   // no effect
    TXIE = 0;   // disable tx interrupts
    RCIE = 0;   // disable rx interrupts
}

char read_eeprom (unsigned char add)
{
    unsigned char a;
    EEADR=add; //adddress location
    EEPGD=0;//point eeprom
    RD=1;//to start rread operation
    while(RD==1);//wait to complete read operation
    a=EEDATA;//data is in EEDATA
    return a;
}

void write_eeprom(unsigned char add, unsigned char a)
{   //////EECON1reg=EEPGD — — — WRERR WREN WR RD/////
    EEADR=add;//adddress location
    EEDATA=a;//data
    EEPGD=0;//point eeprom
    WREN=1;//enable program operation
    //EEIF=0;
    EECON2=0x55;
    EECON2=0xAA;
    WR=1;
    WREN=0;//disable program operation
    while(EEIF==0);//wait to complete write
    EEIF=0;
}

void main( )
{
    unsigned int cutoff=127, reading, reading1;
    init_rs232( );
    TRISA=0xFF;    // Port A inputs
    TRISB=0xF0;    // Port B0-B3 outputs
    TRISD=0x00;
    ADCON1=0b01001110; //Set ADFM (bit 7 of ADCON1) to 0 for left justified
    ADCON0=0b10000000;


    while (1)
    {
        __delay_ms(100);
        ADCON0=ADCON0|1;
        GO = 1; //Start A/D Conversion
        while(GO==1); //Wait end of conversion (conversion complete)

        cutoff = read_eeprom(100);
        reading = ADRESH; //Read the data
        if(reading<(cutoff-neutral_zone/2))
        //If analog input less than (2.5-0.5/2) which is 2.25V
        {
            RB0=0; //Turn on GREEN LED
            RB1=1;
            RB2=1;
        }
        else if (reading>(cutoff+neutral_zone/2))
        //If analog input more than (2.5+0.5/2) which is 2.75V
        {
            RB0=1;
            RB1=1;
            RB2=0; //Turn on RED LED
        }
        else
        {
            RB0=1;
            RB1=0; //Turn on YELLOW LED
            RB2=1;
        }

         if (!RA1) //The switch to Pin A1 is pressed
        {
            while(!RA1); //Wait for the switch to release
            __delay_ms(100);
            write_eeprom(100, reading); //Store ADC value into EEPROM
            printf("The cutoff value is %d \r\n", cutoff);
            PORTD=cutoff;
        }
    }
} //End of Program