;	list	p=pic18f452
;	list	p=pic18f252

; *****************************************************************************

 #ifdef __18F452
 	#include p18f452.inc
 #endif

 #ifdef __18F252
	#include p18f252.inc
 #endif

temp	equ	0x00		; RAM file variable
delay	equ	0x01		; delay work area

	org	0x200		; reset vector
	goto	start

	org	0x208		; interrupt vector
	goto	$

	org	0x218		; interrupt vector
	goto	$

	org	0x220
start:
	movlw	0xfe
	movwf	TRISA		; PORTA, bit 0 is now an output

	movlw	0x06
	movwf	ADCON1		; define PORTA mode (analog/digital)

	clrf	temp		; initialize toggle variable
loop:
	movlw	0x01
	xorwf	temp, f

	movf	temp, w
	movwf	PORTA		; toggle pin
	call	_1s_delay	; delay
	goto	loop

;
; 3.6864-MHz clock
;
; 271-ns clock period, 1.08-us machine cycle
;

; approximate 1-second delay
;
_1s_delay:
	movlw	.100
	movwf	delay
dloop:
	call	_10ms_delay
	decfsz	delay, F
	goto	dloop
	return

; 9221-instruction cycles => approximately 10-ms
; (9216 is ideal)
; 
_10ms_delay:
				; (2) to get here
	movlw	.96		; (1)
_dloop:
	call	_100us_delay	; (92)
	addlw	-1		; (1)
	btfss	STATUS, Z	; (1/2)
	goto	_dloop		; (2)
	nop			; (1)
	return			; (2) to get back

; 92-instruction cycles => 99.8 us
;
_100us_delay:
				; (2) to get here
	call	_20us_delay	; (18)
	call	_20us_delay	; (18)
	call	_20us_delay	; (18)
	call	_20us_delay	; (18)
	call	_20us_delay+2	; (16)
	return			; (2) to get back

; 18-instruction cycles => 19.5-us
;
_20us_delay:
				; (2) to get here
	goto	$+2		; (2)
	goto	$+2		; (2)
	goto	$+2		; (2)
	goto	$+2		; (2)
	goto	$+2		; (2)
	goto	$+2		; (2)
	goto	$+2		; (2)
	return			; (2) to get back

; 9-instruction cycles => 9.76-us
;
_10us_delay:
			; (2) to get here
	goto	$+2	; (2)
	goto	$+2	; (2)
	nop		; (1)
	return		; (2) to get back

	end