Program H :

;************************************
; written by :	John Morton			*
; date : 19/08/97				*
; version : 3.0					*
; file saved as : Counter			*
; for PIC54					*
; clock frequency : 3.82 MHz		*
;************************************

; PROGRAM FUNCTION :  To count the number of times a push button is pressed, 
;  resetting after the sixteenth signal.

 		list 	     	P=16C54
		include		"c:\pic\p16c5x.inc"

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

		porta		equ	05
		portb		equ	06
		Counter	equ	08

		org		1FF
		goto		Start
		org		0


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


Init		clrf		porta		; resets I/O ports
		movlw		b'11111100'	; moves the code for a 0 into portb
		movwf		portb		; 

		movlw		b'0001'	; RA0 : push button, RA1-3 : not connected
		tris		porta
		movlw		b'00000000'	; RB0 : not connected, RB1-7 : Seven Seg. Code
		tris		portb		;

		movlw		b'00000111'	; TMR0 prescaled at 256
		option				;
		clrf		Counter	; resets Counter register

		retlw		0


_7SegDisp	
		addwf		PCL		; skips a certain number of instructions
		retlw		b'11111110'	; code for 0
		retlw		b'01100000'	; code for 1
		retlw		b'11011010'	; code for 2
		retlw		b'11110010'	; code for 3
		retlw		b'01100110'	; code for 4
		retlw		b'10110110'	; code for 5
		retlw		b'10111110	; code for 6
		retlw		b'11100000'	; code for 7
		retlw		b'11111110'	; code for 8
		retlw		b'11110110'	; code for 9
		retlw		b'11101110'	; code for A
		retlw		b'00111110'	; code for b
		retlw		b'10011100'	; code for C
		retlw		b'01111010'	; code for d
		retlw		b'10011110'	; code for E
		retlw		b'10001110'	; code for F



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

Start
		call		Init		; sets up inputs and outputs
Main
		btfss		portb, 0	; tests push button
		goto		Main		; if not pressed, loops back
		
		incf		Counter, f	;
		movlw		d'16'		; has Counter reached 16?
		subwf		Counter, w	;
		btfss		STATUS, Z	;
		clrf		Counter	; if yes, resets Counter
		
		movfw		Counter	; moves Counter into the working reg.
		call		_7SegDisp	; converts into 7 seg code
		movwf		portb		; displays value
		
TestLoop	btfsc		portb, 0	; tests push button
		goto		TestLoop	; still pressed, so keeps looping
		
		clrf		TMR0		; resets TMR0
TimeLoop	movlw		d'255'		; has TMR0 reached 255?
		subwf		TMR0, w	; 
		btfss		STATUS, Z	; 
		goto		TimeLoop	; if not, keeps looping
		goto		Main		; 0.07 seconds has passed, so goes to Main	



	END