;----------------------------------------------------------------------------------------------------------
; Program for Motorola 68HC12
; Drives the stepper motor at a rate determined by the switch setting. 
;

;--------------------------------------------------------------------
       
        XDEF main

DDRH:	EQU $25			;Declaring location of Data Direction Reg. H
PORTH:	EQU $24			;Declaring location of Port H
DDRJ:	EQU $29			;Declaring location of Data Direction Reg. J
PORTJ:  EQU $28			;Declaring location of Port J
PORTG:	EQU $31			;Declaring location of Port G
DDRG:	EQU $33			;Declaring location of Data Direction Reg. G


;*********************************

TFLG2:   EQU $008F		; Timer Interrupt Flag 2
TSCR:	 EQU $0086		; Timer System Control Register
TMSK2:	 EQU $008D		; Timer Interrupt Mask Register 2
TCNT:	 EQU $0084		; Timer Count Register
TOI:	 EQU %10000000          ; Timer Overflow Interrupt enable
TOF:	 EQU %10000000		; Timer Overflow Flag
TEN:	 EQU %10000000		; Timer Enable 
TOFVEC:  EQU $00D0		; Timer Overflow Flag Vector		
Ntimes:	 EQU 30			; Number of times flag needs to be set


		
myData: section



locData: section


;********************************
DISPLAY DS.B  1			; Allocating space for DISPLAY - one byte
COUNT	DS.B  1			; Allocating space for COUNT - one byte
;*******************************
 	



data:	dc.b 12, 4, 6, 2, 3, 1, 9, 8		; The array that holds all values of the stepping sequence

myCode: section


;--------------------------------------------------
; INITIALIZATION
;--------------------------------------------------
main:

    	LDS   	#$07FF 		; Initialize Stack
	LDAA 	#0		; Sets input direction
	STAA	DDRH		; to DDR H
	LDAA 	#$FF		; Makes Port G & J output
	STAA 	DDRG		
	STAA    DDRJ

;************************************************
	LDAA	#TOF		;Clear the flag before starting the time
	STAA	TFLG2		
	
	BSET	TSCR,#TEN	;Enable the timer
	
	
 	
;******************************************************

;--------------------------------

	SEI			; Set interrupts off
	CLR	COUNT		; Clear count
	LDAA	TOF		; Clear TOF first	
	STAA	TFLG2		
	LDAA	#TOI		;Enable Timer overflow interrupt
	STAA	TMSK2		
	CLI			; Set interrupts on


	JMP TOFISR		; Jump to TOFISR


;---------------------------------------------------
; STEPPER MOTOR ACTION
;-----------------------------------------------------
	

start:	LDX	#data		; Load Register X from array
next:	LDAA	0,X		
	STAA	PORTG		; Store the value to port G in order to move the stepper motor	



HERE: 	BRA	HERE		; Wait HERE for interrupt

	

	
RUN:	BSR	Switch1		; Branch to subroutine "Switch 1"
	LDAB	PORTH
	ANDB	#$01 		; Check Switch 8
	BNE	reverse		; Branch if not equal to reverse

forward:			
	INX			; Increment X
	CPX	#data+8		; Compare it 
	BNE	next		; If not equal goto next
	BRA	start		; Always branch to start
	
reverse:			
	DEX			; Decrement X
	CPX	#data-1		; Compare it 
	BNE	next		; If not equal goto next
	LDX	#data+7		; Load register X from array
	BRA	next		; Always branch to next
	

;---------------------------------------------------
; INTERRUPT SERVICE ROUTINE
;-------------------------------------------------

TOFISR:
	INC	COUNT		; Increment COUNT
	LDAA	COUNT		; Load accumulator A from COUNT
	CMPA	#Ntimes		; Compare it with the number of times flag needs to be set
	BNE 	ENDIF		; If not equal branch to ENDIF
	
	INC 	DISPLAY		; Increment DISPLAY
	STAA	DISPLAY		; Store value to DISPLAY 
	STAA 	PORTJ		; Store it to port J (LEDs)
	
	JSR	RUN		; Jump to subroutine RUN
	CLR	COUNT		; Clear COUNT
ENDIF:	LDAA	#TOF		; Clear flag
	STAA 	TFLG2
	RTI			; Return from interrupt
	
	


;---------------------------------------------
;  DELAY
;----------------------------------------------

	
Switch1:
	LDAB	PORTH	 	; Check	Switch 1
	ANDB	#$80	
	BEQ	Switch1		; Branch if equal to Switch1
	
	
switch7:		
	LDAA	PORTH		; Check switch 7
	ANDA 	#$02
	BNE	delay		; Branch if not equal to delay
back:
	RTS			; Return from subroutine 
	
	
delay:  LDAA #Ntimes		; Initialize COUNT to wait for Ntimes
	STAA COUNT		
	
wait1:	BRCLR  	TFLG2,#TOF,wait1  ; Poll the TOF bit and branch when the bit is set to 1
		
	LDAA	#TOF		; CLear the TOF flag
	STAA	TFLG2
		
	DEC	COUNT		; Decrement the counter
	BNE 	wait1		; Branch if not equal to wait1
	BRA	back		; Always branch to back