;*************************************************************************
; Project:        Hallo World - LED at PORTB.0 is flashing
; Project file:   hallo_world.mcp 
; Source file:    hallo_world.asm 
; Author:         Knorr 
; Date:           02.02.2008 
; Software:       MPASM                                           
; Hardware:       PIC16F84A Programmer Module
;
; National language Code page: 850   (OEM - Multilingual Latin I)
;*************************************************************************

; ------------------------------------------------------------------------
; includes
; ------------------------------------------------------------------------
	include "p16f84a.inc"               ; definition for target controller

;-------------------------------------------------------------------------
; PIC configuration
; ------------------------------------------------------------------------
      LIST  p=16f84a
      
; define configuration word 
; code protection off/ power up timer off/ wdt off /XT oscillator
      __config    0x3ff9      

; ------------------------------------------------------------------------
; Variables definition
; ------------------------------------------------------------------------
ct1	        equ		h'10'
ct2		equ		h'11'
ct3		equ		h'12'
ct4             equ             h'13'

; ------------------------------------------------------------------------
; RESET Vector
; ------------------------------------------------------------------------
            org   0x000
            goto  start
; ------------------------------------------------------------------------
; main program
; ------------------------------------------------------------------------
start:                        ; configure Port A and B

            bsf   STATUS,RP0  ; switch to register bank 1
            movlw 0x00 ; PortB.0 define as output
            movwf TRISB       ; write direction register 
            movlw 0xff        ; PortA define as input
            movwf TRISA       ; write direction register
            bcf   STATUS,RP0  ; switch to register bank 0

	    clrf  PORTB       ; set Port B to 0

main:      
btfss PORTA,0
goto loop
movlw 0x01
xorwf PORTB,1
call delay1sec

loop:
btfss PORTA,1
goto loop1
movlw 0x02
xorwf PORTB,1
call delay1sec

loop1:
goto  main        ; go back to main
 
; ------------------------------------------------------------------------
; time delay
; 164*(1+2)*1æs +8æs =500æs (1 Machine cycle = 1æs if clock frequency is 4MHz )
; ------------------------------------------------------------------------
delay500us:						; (2MC) from the jump to subroutine
		movlw   D'164'        	; (1MC) load register w with constant
		movwf   ct1         	; (1MC) move content of register w to ct1
		nop						; (1MC)
w01:
		decfsz  ct1,f      	    ; (1MC) decrement ct1 with target f
		goto    w01            	; (2MC) if ct1 != 0 -> w01, in other case 
								;       skip the instruction
		return					; (2MC + 1MC for NOP when 0)

; ------------------------------------------------------------------------
; time delay
; 200 * delay500us = 100ms
; ------------------------------------------------------------------------
delay100ms:
		movlw   D'200'        	; load register w with constant
		movwf   ct2         	; move content of register w to ct2
w02:
		call    delay500us      ; call the subroutine
		decfsz  ct2,f      		; decrement ct2 with target f
		goto    w02            	; if ct2 != 0 -> w02, in other case 
								; skip the instruction
		return

; ------------------------------------------------------------------------
; time delay
; 5 * delay100ms = 500ms
; ------------------------------------------------------------------------
delay500ms:
		movlw   D'5'        	; load register w with constant
		movwf   ct3         	; move content of register w to ct2
w03:
		call    delay100ms      ; call the subroutine
		decfsz  ct3,f      		; decrement ct3 with target f
		goto    w03            	; if ct3 != 0 -> w03, in other case 
								; skip the instruction
		return

; ------------------------------------------------------------------------
delay1sec:
		movlw   D'2'        	; load register w with constant
		movwf   ct4         	; move content of register w to ct2
w04:
		call    delay500ms      ; call the subroutine
		decfsz  ct4,f      		; decrement ct3 with target f
		goto    w04            	; if ct3 != 0 -> w03, in other case 
								; skip the instruction
		return

; ------------------------------------------------------------------------
        end