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