;;; Introduction to LEDs
;
; Written by: Nora Znotinas
; Last modified: January 12, 2005
;

; Light the 'Left LED', connected to port A pin RA3, with an equal interval pattern.
; Timing accomplished using a delay routine.
;

;;; assembler directives
	LIST	P=PIC18F452, F=INHX32, C=160, N=0, ST=OFF, MM=OFF, X=ON
	#include	P18F452.INC


	CONFIG	OSC=HS			;select HS oscillator
	CONFIG	PWRT=ON, BOR=ON, BORV=42	
	CONFIG	WDT=OFF, LVP=OFF	;disable watchdog timer
					; and low voltage power

;;; variables

	cblock	0x000
	max_loops		;number of loops
	max_count		;delay loop counter
	endc

;;; macro definitions

;   movlf - command to move a literal value into a file register

movlf	macro	imm,dest
	movlw	imm
	movwf	dest
	endm

;;; vectors

	org	0x0000	;reset vector
	goto	start	;start of program

	org	0x0008	;high priority interrupt vector
	goto	$	;none for now

	org	0x0018	;low priority interrupt vector
	goto	$	;none for now

;;; the actual program

start

; initialize PORT A registers
	movlf	b'01100001',TRISA	;set data direction
	movlf	b'10001110',ADCON1	;set digital/analog functions
	clrf	PORTA			;initialize L, C, R LEDs to off

main_l	rcall	delay			;wait
	bsf	LATA,3			;turn left LED on
	rcall	delay			;wait
	btg	LATA,3			;turn left LED off
	bra	main_l

;;; delay subroutine
delay	setf	max_loops		;initialize number of loops
del_out	setf	max_count		;initialize loop counter
del_in	nop				;kill some time
	decfsz	max_count		;decrement count
	bra	del_in			;loop if not zero
	decfsz	max_loops		;   else decrement loop number
	bra	del_out			;loop if not zero
	return				;   else return

	end