;**********************************************************************
;    Title:	    	Push-Button                                       *                                                                  *
;    Filename:	    f684code.asm                                      *
;    Date:          28.01.2007                                        *
;    Author:        Stefan Bracher (http://stefan.bracher.info)       *
;**********************************************************************
;    A simple push-button LED switch. First time the button is		  *
;    pressed, the LED goes on, the second time it goes off...         *
;                                                                     *
;    Could be used to control the light in a room with several        *
;    switches in parallel. (Of course some additional circuitry       *
;    for the power part would be needed)                              *
;**********************************************************************


	list		p=16f684		; list directive to define processor
	#include	<P16F684.inc>	; processor specific variable definitions
	
	__CONFIG    _CP_OFF & _CPD_OFF & _BOD_OFF & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT & _MCLRE_OFF & _FCMEN_OFF & _IESO_OFF

; '__CONFIG' directive is used to embed configuration data within .asm file.
; The labels following the directive are located in the respective .inc file.
; See respective data sheet for additional information on configuration word.


;***** VARIABLE DEFINITIONS
w_temp		EQU	0x71			; variable used for context saving
status_temp	EQU	0x72			; variable used for context saving
temp		equ	0x25  			; Temporary variable
pa5_in		equ 0x26			; Input PA5
pa5_in_old	equ 0x27			; Input PA5(@ t=t-1)
my_status	equ 0x28			; myStatus (1=on, 0=off)


;******MACROS****************
BANK1	MACRO
	BSF		STATUS, RP0			;MACRO TO SELECT BANK 1
	ENDM	

BANK0	MACRO
	BCF		STATUS, RP0			;MACRO TO SELECT BANK 0
	ENDM
;**********************************************************************
	ORG		0x000			; processor reset vector (here the PIC starts)
	BANK0					; Change to Bank 0
	MOVLW  	0h				; w=0h
	MOVWF	pa5_in			; pa5_in=w (=0h)
	MOVWF	pa5_in_old		; pa5_in_old=w (=0h)
	MOVWF	my_status		; my_status=w (=0h)
	call port_con			; Call Function port_con
	goto MAIN

;******FUNCTIONS****************  
port_con
	BANK0					; Change to Bank0 (where PORTA and CMCONO are stored)
	CLRF	PORTA			; Clear PORTA
	MOVLW	B'00000111'		; w=B'00000111'
	MOVWF	CMCON0			; CMCONO=w (=B'00000111' -> COMPARATORS ARE OFF)
	
	BANK1					; Change to Bank1 (where ANSEL and TRISA are stored)
	CLRF 	ANSEL			; clear ANSEL -> set digital I/O 
	MOVLW 	B'00101000'		; B'00100000'
	MOVWF	TRISA			; TRISA=w (=B'00101000' -> RA0, RA1, RA2, RA4=output)
	BANK0					; Change to Bank0
	retlw	0				; Return with w=0

Turn_on
	MOVLW 	B'00001'		; w=B'00001'
	MOVWF	PORTA			; PORTA=w (=B'00001' -> RA0 high)
	RETURN

Turn_off
	MOVLW 	B'000000'		; w=B'00000'
	MOVWF	PORTA		 	; PORTA=w (=B'00000' -> all low)
	RETURN

READ_PORTA	
	BTFSC 	PORTA, 5		; If bit 5 in PORTA is 1
	MOVLW	01h				; w=01h
	BTFSS 	PORTA, 5		; If bit 5 in PORTA is 0
	MOVLW	00h				; w=00h
	MOVWF	pa5_in;			; pa5_in=w (-> write the input in RA5 in pa5_in)
	RETURN 

Status_OFF
	call Turn_off		; turn light off
	MOVLW 01h			; w=1
	BTFSC temp, 0		; if temp==1	
		MOVWF my_status ; my_status=w (=1)
	BTFSC temp, 0		; if temp==1
		MOVLW 00h		; w=0
	BTFSC temp, 0		; if temp==1
		MOVWF temp		; temp=w (=0) (to avoid doublechanges of status)
	RETURN

Status_ON
	call Turn_on		; turn light on
	MOVLW 00h			; w=0
	BTFSC temp, 0		; if temp==1	
		MOVWF my_status	; status=w (=0)
	BTFSC temp, 0		; if temp==1	
		MOVWF temp; 	; temp=w (=0) (to avoid doublechanges of status)
	RETURN
;****************************************************************************

;****MAIN****************************************************************
MAIN


	call READ_PORTA			; Read PORTA (the input in RA5 is stored in pa5_in, see function READ_PORTA)
	MOVFW	pa5_in_old		; w=pa5_in_old
	SUBWF	pa5_in, 0		; w=pa5_in-pa5_in_old 
	MOVWF	temp			; temp=w
	BTFSC 	temp, 1			; if (temp==255)or(temp==2)
	MOVLW	00h				; w=0
	MOVWF 	temp			; temp=w (-> temp=1 if the button is pressed down)
	BTFSS 	my_status, 0	; If (Status==0)
	call Status_OFF			; 	
	BTFSC 	my_status, 0	; If (Status==1)
	call Status_ON			; 			
	MOVFW pa5_in			; w=pa5_in
	MOVWF pa5_in_old		; pa5_in_old=w
	goto MAIN

	END                       ; directive 'end of program'