*==============================================================
* testint.asm - Demonstrates the interrupt function of the HC11.
*
* Usage: In THRSIM, connect a switch to the IRQ pin, and bring 
*	up the I/O box.  Set up the memory map and run the program.  
*	The register D lights will count continuously.
*	The register B lights will count from 0-255 whenever
*	the switch first goes low.
*===============================================================
#include "registers.asm"	; Declares the HC11 control registers.
#include "vectors.asm"		; Declares interrupt & reset vectors.

	org	$2000		; Locate our program at address $2000, in external RAM.
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.

* 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.