Please help me find the reference voltage in my program

off_time_counter

hi, i am using pic 16f877. and below is a program. Can anyone tell me how should i know the reference voltage as they are all hex numbers. thanks a lot

//Sample program for AdvFamLab

//Include required header files here
#include<pic1687x.h>
#include<pic.h>

//Declare global variables here
volatile int on_time_counter, off_time_counter;
volatile unsigned char light=0;
int timer_value=0xFE;

//Declare functions to be used in the program, i.e.
//void initialize_IO_ports(void)
//void initialize_ADC(void)
//int read_ADC_channel(unsigned int)
//void initialize_timer1(int)
//Put the body of all the functions

void initialize_IO_ports(void)
{
//set the digital IO ports as per requirement
TRISA = 0xFF ; //portA as input
TRISB = 0xFF ; //portB as input
TRISC = 0x00 ; //portC as output
TRISD = 0x00 ; //portD as output
ADCON1= 0x82 ; //set PortE as digital io and portA as analog, and VDD and VSS; ADC output is right-justified.
//clear the output ports at the beginning
PORTD = 0x00 ; //clear portD
PORTC = 0x00 ; //clear portC
}

void initialize_ADC(void)
{
//enable the ADC
ADON=1;
//set clock source for the ADC
ADCS1=0;
ADCS0=0;
}

int read_ADC_channel(unsigned int channel_number)
{
int value;
switch(channel_number)
{
case 0:
//set the channel selector
CHS2=0;
CHS1=0;
CHS0=0;
case 1:
//set the channel selector
CHS2=0;
CHS1=0;
CHS0=1;
default:;
}
//start AD conversion
ADGO=1;
//wait for conversion to finish
while(ADGO)
{};
//read the values in the registers
value=( ADRESH<<8 )+ADRESL;
return(value);
}

void initialize_timer1(void)
{
//The following SFR are to be set as given in the Timer1 Chapter of PIC datasheet
//set prescalar value of 1:8
T1CKPS1=1;
T1CKPS0=1;
T1OSCEN=1; //Timer1 oscillator is enabled
//set internal clock i.e. FOSC/4..eg. 20MHz osc so clk for TMR1 is 5MHZ or 200ns per TMR1 count
TMR1CS=0;
GIE=1; //global interrupt enabled
PEIE=1; //peripheral interrupt enabled
TMR1IE=1; //enable timer1 interrupt
}

void load_timer1(int timer_value)
{
TMR1ON=0; //disable timer1 before loading the values
TMR1IF=0; //timer1 flag cleared
TMR1H=(0xFFFF-timer_value)>>8; //load timer1 high register
TMR1L=(0xFFFF-timer_value)&0xFF; //load timer1 low register
TMR1ON=1; //enable timer1
}

//the interupt service routine
void interrupt isr0(void)
{
if(TMR1IF==1)
{
//At the start of interrupt service routine, reload timer
//load_timer1(timer_value);
TMR1ON=0; //disable timer1 before loading the values
TMR1IF=0; //timer1 flag cleared
TMR1H=(0xFFFF-timer_value)>>8; //load timer1 high register
TMR1L=(0xFFFF-timer_value)&0xFF; //load timer1 low register
TMR1ON=1; //enable timer1
if(light==0)//if light was off
{
off_time_counter++; //increment off_time_counter
if(off_time_counter==250) //if off_time_counter has reached the required count
{
off_time_counter=0; //clear off_time_counter
on_time_counter=0; //clear on_time_counter
light=1; //set the light On again
}
}
else if(light==1)//if light was On
{
on_time_counter++; //increment on_time_counter
if(on_time_counter==50) //if on_time_counter has reached the required count
{
off_time_counter=0; //clear the off_time_counter
on_time_counter=0; //clear the on_time_counter
light=0; //clear the light Off
}
}
}
}

//main function
int main()
{
//Declare the variables for the main function here
int analog_value1;
initialize_IO_ports();
initialize_ADC();
initialize_timer1();
load_timer1( timer_value);
//put the infinite loop here
while(1)
{
//read the digital input and set the output
PORTD = PORTB ; //read portB and output it to portD.
//output the light according to the variable 'light'
RC0=1;
RC1=1;
RC2=0;
RC3=light;
RC4=0;
//read the analog channel and store the value in the variable;
analog_value1=read_ADC_channel(0);
//check the range of the value and set or clear the RC5 accordingly
if((analog_value1>0x004F)&&(analog_value1<0x01FF)) RC5=1;
else
RC5=0;
};
return(1);
}
//the end of AdvFamLab sample program

ADC reerence voltage

looks like the ref voltage range is 0.4V to 2.55V
considering the Vcc as 5V and the adc resolution is 4.9mV.
just cross check it.