* testint.asm - Test interrupt function of HC11.

#include "registers.asm"	; Declares the HC11 control registers.
#include "vectors.asm"		; Declares interrupt & reset vectors.

	org	$2000
main:

* Set IRQ for falling-edge-detect mode.
* This must be done in the 1st 64 cycles out of reset.
	ldx	#OPTION		; Point X at the OPTION register
	bset	0,X IRQE	; Set the IRQE bit in the OPTION register
		
* Turn on bits DDRD0-DDRD5 in data direction register D to make PD0-PD5 outputs.
	ldx	#DDRD
	bset	0,X DDRD5|DDRD4|DDRD3|DDRD2|DDRD1|DDRD0

	cli		; Clear I interrupt mask (enable IRQ interrupts) 
loop1:	inc	PORTD	; Increment port D contents.
	bra	loop1	; Just keep doing this forever.


myISR:	inc	PORTB	; Increment port B contents.
	bne	myISR	; Keep going till it gets back to 0.
	rti		; Return from interrupt.

*----------------------------------------------------
* EEPROM region
* Establish our interrupt and reset vectors in ROM.
*----------------------------------------------------

	org	VIRQ	; Point the IRQ interrupt vector...
	fdb	myISR	; ...at my Interrupt Service Routine.

	org	VRST	; Point the RESET vector...
	fdb	main	; ...at my main routine.