#include <htc.h>
__CONFIG(INTIO & WDTDIS & PWRTDIS & MCLRDIS & UNPROTECT & BORDIS & IESODIS & FCMDIS);
#define bitset(var,bitno) ((var) |= 1 << (bitno))
#define bitclr(var,bitno) ((var) &= ~(1 << (bitno)))

void io_port_setup(void)
{
	// 3 ways to disable the A to D converter;
	// ADCON0 &= 0b11111110;
	// bitclr(ADCON0,0);
	ADON = 0;

	// Make sure that no pin is connected to the A/D
	ANSEL = 0b00000000;
	ANSELH = 0b00000000;

	// Sets all bits for port C for output
    TRISC = 0b00000000;
	// All bits for port C are off
    PORTC = 0b00000000;

	// Sets all bits for port A for input
	TRISA = 0b00111111;
	// Sets bit 3 of port A to trigger an interrupt on change
	IOCA = 0b00001000;

	// Clears PORTA/B interrupt flag
	RABIF = 0;
	// Allows PORTA/B to trigger an interrupt 
	RABIE = 1;
}

void timer_setup(void)
{
	// Set all the parameters for Timer0
	// See section 5.1.3
	#asm
	clrwdt
	#endasm
	// Selects the processor clock for Timer0 (See OPTION reg)	
	T0CS = 0;
	// Selects the pre-scaller for Timer0 (See OPTION reg)
	PSA = 0;
	// Sets the pre-scaller value to 256
	OPTION = ((OPTION & 0b11111000) | 0b00000111);
	// Loads Timer0 register
	TMR0 = 0;
	// clear Timer0 interrupt flag (see INTCON)
	T0IF = 0;
	// Allows Timer0 to generate an exception (see INTCON)
	T0IE = 1;
}

static void interrupt interupt_handler(void)
{
	// Was the interrupt generated by Register A/B?
	if (RABIF == 1)
	{
		if (RA3 == 1)
		{
			bitclr(PORTC,3); 
		}
		else
		{
			bitset(PORTC,3);
		}
		// clears the RegiterA/B interrupt flag
		RABIF = 0;
	}
	// Was the interrupt generated by Timer0?
	if (T0IF == 1)
	{
		// Resets the value of Timer0
		TMR0 = 0;
		PORTC ^= 0b00000001;
		// clears the Timer0 interrupt flag
		T0IF = 0;
	}
}


void main( void)
{
	// set the oscillator speed to 1 MHz
	OSCCON = ((OSCCON & 0b10001111) | 0b01000000);

	// setup the ports
	io_port_setup();

	// setup the timer
	timer_setup();

	// Interrupts are on
	GIE = 1;

	// Loop for ever
	while (1)
	{
	}
}