;***************************************************************************
;* 
;* 
;* File Name            :"Debounce.asm"
;* Title                : Debouncing of a single key
;* Date                 : 09.01.05	13:09
;* Version              : 1.0
;* Status				: no known problems
;* 
;* Target MCU           :AT90S8515
;*
;* DESCRIPTION		:			 
;*			 Key 0 debounced toggling all LEDs 
;*
;*************************************************************************** 

.include "8515def.inc"

.def	CNT = R25		; Debounce Counter
.def	LEDOUT = R0	; LED output register

;***** Code

	rjmp	RESET		;Reset Handle


RESET:	     ; Put Stack Pointer at End of Ram after each Reset
	ldi 	R16,low(RAMEND)	; Load low byte address of end of RAM into R16
	out		SPL,R16			; Initialize stack pointer to end of int. RAM
	ldi 	R16,high(RAMEND); Load high byte address of end of RAM into R16	
	out 	SPH,R16			; Initialize high byte of stack pointer 

	     ; Initialize Ports A,B,C and D at the beginning of the Program

INITP:
	ser		r16				; Port C used as Outputs for LEDs
	out		DDRC,r16		; 
	clr		r16				; Port D used as Inputs for Switches
	out		DDRD,r16		; 
	mov		r0,r16
	out		PORTC,r0		; Switches all LEDS on


		; Read key 0 and debounce

Key0:	clr  	CNT
Again0:	sbic	PIND,0
		rjmp	Key0		; Jump if key is not pressed or bouncing
		dec		CNT
		brne	Again0
Keypressvalid:
		com		r0
		out		PORTC,r0

Not0:	clr  	CNT
Not0Ag:	sbis	PIND,0
		rjmp	Not0		; Jump if key is not released yet or bouncing
		dec		CNT
		brne	Not0Ag

Keyreleasevalid:
		rjmp	Key0