PROGRAM B

;************************************
; written by :	John Morton			*
; date : 21/07/97				*
; version : 1.0					*
; file saved as : PushButtonA		*
; for PIC16F54				*
; clock frequency : 3.82 MHz		*
;************************************

; PROGRAM FUNCTION : If a push button is pressed an LED is turned on

 		list 	     	P=16F54
		include	"c:\pic\p16f5x.inc"

		__config	_RC_OSC & _WDT_OFF & _CP_OFF

;============
; Declarations :  

porta		equ		05
portb		equ		06

		org		1FF
		goto		Start
		org		0

;===========
; Subroutines : 

Init		clrf		porta		; resets inputs and outputs
		clrf		portb		;
		movlw		b'0000'		; RA0 : LED, RA1-3 : not connected
		tris		porta
		movlw		b'00000001' 	; RB0 : push button, RB1-7 : N/C
		tris		portb
		retlw		0

;=============
; Program Start : 

Start		call		Init		

Main		btfss		portb, 0	; tests push button, skip if pressed
		goto		LEDOff		; push button isn't pressed so turns 
						;  LED off
		bsf		porta, 0	; push button is pressed so turns LED on
		goto		Main		; loops back to Main
LEDOff		bcf		porta, 0	; turns LED off
		goto		Main		; loops back to Main

		END