;******************************************************
;*               EXT_INT.ASM
;* INTCON外部中斷設定，RB0 外接按鍵按下，觸發外部中斷
;******************************************************
			list p=16F877		
#include 		<p16f877.inc>
;
VAL_US		equ	.249			; 1ms delay 給定初值
VAL_MS		equ	.250			; 呼叫1ms Delay之次數
VAL_S		equ	.4
count		equ	0x20		; 1ms delay 變數位址
count_ms		equ	0x21   		 ; 呼叫1ms Delay之變數位址.
count_s		equ	0x22
;
;******  程式開始 *********************
			org 	0x00		; reset vector
			nop				; Reserve for MPLAB-ICD
			goto	start
			org	0x04
			goto	isr
start:	
			clrw
			clrf		PCLATH
			banksel	TRISC	; Select to bank1
			clrf		TRISC	; PORTC = Output
			banksel 	PORTC 	; Select to bank0
			clrf		PORTC		; Clear PORTC

			bsf	INTCON,GIE
			bsf	INTCON,INTE
inc:			
			incf	PORTC,f
			call	delay_250ms
			goto	inc
			
isr:			
			
			movlw 	B'11111111'
			movwf	PORTC
			call	delay_250ms
			bcf	INTCON,INTF
			
			retfie
						
;
;-------- 1s delay routine ----------
;delay_s:	
;			movlw	VAL_S		 
;		movwf	count_s
;loop_s		call 		delay_250ms
;			decfsz	count_s,f
;			goto		loop_s
;		return

;-------- 250 ms delay routine ----------
delay_250ms:	
			movlw	VAL_MS		 
		movwf	count_ms
loop_ms		call 		delay_1ms
			decfsz	count_ms,f
			goto		loop_ms
		return
;
;-------- 1 ms delay routine -----------
delay_1ms:
			nop			 
		movlw	VAL_US		 		
			movwf	count
dec_loop	nop
			decfsz	count,f
		goto 	dec_loop
			return
;	



		
		end