*******************************************************************************
* Example of using bset/bclr for managing the enabling/disabling of a system.
*******************************************************************************

	org	$3000

START

_main:	jsr	_enable
	jsr	_enable		; should not print
	jsr	_disable
	jsr	_disable	; should not print

	move.b	#9,d0		; exit
	trap	#15

* macro for printing a given null-terminated string
print	MACRO
	lea	\1,a1
	move.l	#13,d0		; print null-terminated string
	trap	#15
	ENDM

*******************************************************************************

* Enabled the system.  Do not re-enable if already enabled.
_enable:
	bset	#ENABLED,FLAGS
	bne	enDone		; if already enabled, return

	print	_msg1

enDone
	rts

* Disable the system.  Do not re-disable if already disabled.
_disable:
	bclr	#ENABLED,FLAGS
	beq	disDone		; if already disabled, return

	print	_msg2

disDone
	rts

*******************************************************************************

FLAGS	dc.b	0
ENABLED	equ	0

_msg1	dc.b	'Enabling...',0
_msg2	dc.b	'Disabling...',0

	end	START