lab2.asm

pic单片机资料

		#INCLUDE p16F877A.inc	; Include the standard definitions

		clrf	PORTB		; Initialize PORTB so that all LEDs are off by default
		BANKSEL	TRISB		; BANKSEL is used to get to bank with TRISB in it (bank 1)
		clrf	TRISB		; Clear TRISB to make all PORTB pins outputs
		movlw	B'00010000'	; Make pin RA4 an input (rest of PORTA pins are outputs)
		movwf	TRISA		; This is redundant as TRISA bits are 1抯 by default (inputs)
							; (the rest of the pins are set low)

		movlw	H'07'		; Writing 7 into ADCON1 causes all analog pins to allow
		movwf	ADCON1		; digital input.  You must set ADCON1 when using pins with 
							; A/D functions as they are analog mode by default.
							; This code isn抰 needed in this example - do you know why?

		BANKSEL	PORTA		; BANKSEL is used to return to bank 0 (for PORTA, PORTB)
Loop
		btfss	PORTA,4		; Test RA4 on PORTA, skip if pin is high
		goto	On			; go to "On" code if button is pressed (pressed button is low)

Off		
		movlw	B'00000010'	; "On" code is skipped so "Off" code runs - it writes a value to
		movwf	PORTB		; PORTB to turn on RB1 (high) and sets rest of PORTB low
		goto	Loop		; The test of the button happens again by branching to 揕oop