void timer0_enable (void) {
    /* Initialise Timer 0 */
    OPTION = 0b11010111;  /* Set TMR0 to Internal CLk, 1:256 */
    T0IF = 0;             /* Clear TMR0 Flag, ready for use */
    T0IE = 1;             /* Enable Timer Overflow Interrupt */
}

void initialize_IO_ports (void) {
	//set the digital IO ports as per requirement
	TRISA = 0xFF ; //portA as input
	TRISB = 0B10000000 ; //portB as input
	TRISC = 0B11110000; //portC as output
	TRISD = 0B10000000; //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
	 
	GIE=1; //global interrupt enabled
 	PEIE=1; //peripheral interrupt enabled
}

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

int read_ADC_channel (unsigned int channel_number) {
	int value;
 	switch (channel_number) {
		case 0: 
			CHS2=0; 
			CHS1=0; 
			CHS0=0;
 		case 1: 
			CHS2=0; 
			CHS1=0; 
			CHS0=1;
		case 2: 
			CHS2=0; 
			CHS1=1; 
			CHS0=0;
		case 3: 
			CHS2=0; 
			CHS1=1; 
			CHS0=1;
		default:;
 	}
 	ADGO=1; //start AD conversion
 	while(ADGO) {}; //wait for conversion to finish
 	value=(ADRESH<<8)+ADRESL; //read the values in the registers
 	return value;
}

void interrupt isr0 (void) {
	// for timer0
	if (T0IF == 1) { 
		luggage_present = luggage_ispresent();
		T0IF = 0;	// timer0 reload 
	}
}

void main() {

	int myInt;

	timer0_enable();	
	initialize_IO_ports();
	lcd_init();
	initialize_ADC();

// below is just a debugging tool to print ADC values