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#INCLUDE	'A:\VAR_DEF.ASM'

* Define program variables
	ORG	DATA
S0	RMB	1
S1	RMB	1
S2	RMB	1
S3	RMB	1
S4	RMB	1
S5	RMB	1
S6	RMB	1
S7	RMB	1
STEP	RMB	1	; +1=FORWARD; -1=BACKWARD
POINTER	RMB	1


* Main program
	ORG	PROGRAM
START	LDX	#REGBAS
* Initialize stepper motor sequence
	LDAA	#$08
	STAA	S0
	LDAA	#$09
	STAA	S1
	LDAA	#$01
	STAA	S2
	LDAA	#$05
	STAA	S3
	LDAA	#$04
	STAA	S4
	LDAA	#$06
	STAA	S5
	LDAA	#$02
	STAA	S6
	LDAA	#$0A
	STAA	S7
* Initialize controls
	LDAA	#0	; set stand still as default
	STAA	STEP
	LDAA	#$00	; set pointer
	STAA	POINTER	
* Start looping
LABEL0	JSR	STEP_SR
	BRA	LABEL0
	SWI

* Step subroutine
STEP_SR	LDAB	POINTER	; load pointer in B
	ADDB	STEP	; add step to pointer -> B
	CMPB	#7	; check roof
	BLE	LABEL3	; bypass if the roof not hit yet
	LDAB	#0	; reset pointer to the bottom
LABEL3	CMPB	#0	; check if bottomed out
	BGE	LABEL4	; jump if bottom not hit yet
	LDAB	#7	; reset pointer to the roof
LABEL4	STAB	POINTER	; store pointer
	LDY	#$0000	; zero Y	
	ABY		; B+Y -> Y. We have the pointer in Y
	LDAA	$00,Y	; load sequence code into accA from 
*			: the location indicated by pointer
	STAA	PORTB,X	; send sequence code to PORT B
	RTS

	ORG	RESET	; reset vector
	FDB	START	; set to start of program