; File STEP508.ASM
; ... for PIC12C508A microcontroller
; Program to use PIC as a step and direction controller for a unipolar
; step motor.  Step and direction pins are GPIO-5, GPIO-3; GPIO_0, GPIO_1, GPIO_2, GPIO_4,  are ; the windings; in order (driven by NPN small sig transistors or MOSFETS)
; Steps on negative going edge of step pulse.

; CPU configuration
; 	(It's a 12C508A, Internal RC oscillator,
; 	watchdog timer off, power-up timer on)
	LIST   P=12C508A
	processor 12c508A
	include	  <p12c508A.inc>
;	__config  _IntRC_OSC & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF

; Declare variables

pattA	equ	H'0D'	;Current step pattern number (0-7) for axis A
lastA	equ	H'0E'   ;Last state of step pin on axis A (1 is high, 0 is low)
inport	equ	H'11'	;Value of port A when read (stored for later access)
temp	equ	H'12'

#DEFINE STEP	inport,5	; Step pulse input
#DEFINE DIR	inport,3	; Direction Input

OPMASK	EQU	B'11000000'
IOMASK	EQU	B'00101000'	; all bits output (except GP3 and GP5)
                                ; GP0 , GP1 , GP2 , GP4  controls The stepper Coils
                                ; GP3 controls direction
				; GP5 Controls Step Pulses


	
	ORG 0
	
; start of main code
;***************************************************
;
;	START OF PIC 12c508A CODE FOR STEP;
;
;***************************************************
;

;------------------------------------------
;****Power on reset startpoint
;------------------------------------------

;***Initialization of program	
	MOVWF	OSCCAL
	
	MOVLW	OPMASK
	OPTION	

; Set GPIO for input & output	
	
	MOVLW	IOMASK
	TRIS	GPIO		




;Clear port and zero motors


	movlw	B'00000001'
	movwf	GPIO
	clrf	lastA
	clrf	pattA

;Loop around for a while to let everything stabilize

	movlw	d'255'
	movwf	inport
loop:	decfsz	inport, f
;	goto loop

;***Basic program loop

;Main routine - check pin states and step on negative edge
;Get port data and store, then check axis A
;A10 checks if old is 0, new is 1 (update register)
;A01 checks if old is 1, new is 0 (step and update register)
;Similarly for axis B

main:	movf	GPIO, w
	movwf	inport
	CLRWDT
A10:	btfsc	lastA, 0
	goto A01
	btfss	STEP
	goto A01
	bsf	lastA, 0
A01:	btfss	lastA, 0
	goto B10
	btfsc	STEP
	goto B10
	bcf	lastA, 0
	goto stepA

B10:	goto main

;------------------------------------------
;***stepA - sub to cycle axis A one Full step
;  Dir of 1 is increase, else decrease

stepA:	btfss	DIR
	decf	pattA, f
	btfsc	DIR
	incf	pattA, f

;Check for pattern overflow and fix


	movf	pattA, w
	XORLW	D'255'
	movlw	D'07'
	btfsc	STATUS, Z
	movwf	pattA

	movf	pattA, w
	XORLW	D'08'
	btfsc	STATUS, Z
	clrf	pattA	

;Get step pattern and send to GPIO on bits 0-1-2-4

	movf	pattA, w
	call 	dcode
	movwf	GPIO

  goto main



;------------------------------------------
;***stepcode - sub to generate bit pattern for number in w (!!MUST BE 0-7!!)
;  pattern is stored in w register 

dcode:	addwf	PCL, f		;     Use below column for the half Step
	retlw	B'00000001'	;0	retlw	B'00000001'	;0
	retlw	B'00000010'	;1	retlw	B'00000011'	;1
	retlw	B'00000100'	;2	retlw	B'00000010'	;2
	retlw	B'00010000'	;3	retlw	B'00000110'	;3
	retlw	B'00000001'	;4	retlw	B'00000100'	;4
	retlw	B'00000010'	;5	retlw	B'00010100'	;5
	retlw	B'00000100'	;6	retlw	B'00010000'	;6
	retlw	B'00010000'	;7	retlw	B'00010001'	;7


;Mandatory end of program command

	end