Solution to Practical Session 5 | AMI4655 Microcontrollers

Microcontrollers

The exercise involved producing a program to output a binary count sequence on portB after pressing a switch on port A bit RAO.

;The following program will produce a binary count sequence on port B ;after pressing switch A0. ;
	LIST	p=16F84
; **** PROGRAM EQUATES **** ;
pc	EQU	0x02
status	EQU	0x03
porta	EQU	0x05
trisa	EQU	0x05
portb	EQU	0x06
trisb	EQU	0x06
delay1	EQU	0x0c
delay2	EQU	0x0d
delay3	EQU	0x0e
value	EQU	0x12
;
timer	EQU	0x0f
r0	EQU	0x10
r1	EQU	0x11
dat5msh	EQU	.10
dat5msl	EQU	.167
;
rp0	EQU	5
f	EQU	1
w	EQU	1
; ; **** MAIN PROGRAM ****
	ORG	0x00
;
init	BSF	status,rp0	;Select register page 1
	MOVLW	0x00
	MOVWF	trisb	;Set port B all outputs
	MOVLW	0xff
	MOVWF	trisa	;Set port A all inputs
	BCF	status,rp0	;Select register page 0
;
	MOVLW	0xff	;Switch off all LEDs
	MOVWF	portb
	MOVWF	value	;'value' is output value
;
start	BTFSC	porta,0	;Check for RA0 = 0
	GOTO	start	;No, read port A again
;
begin	MOVLW	.20	;Yes set timer value = 20 dec
	MOVWF	timer
	MOVLW	0x01
	SUBWF	value,f	;Subtract 0x01 from value
;
wait	MOVF	value,w
	MOVWF	portb	;Output value to port B
	CALL	dly5ms	;Call delay subroutine
	DECFSZ	timer	;timer:=timer - 1
	GOTO	wait	;if timer != 0 do subroutine again
;
	GOTO	begin	;go back to set timer
; ; **** DELAY SUBROUTINE ****
dly5ms	MOVLW	dat5msh	; - outer delay loop
	MOVWF	r0
;
dly5ms1	MOVLW	dat5msl	; -inner delay loop
	MOVWF	r1
;
dly5ms2	DECFSZ	r1	; -inner delay loop
	GOTO	dly5ms2
	DECFSZ	r0
	GOTO	dly5ms1	;- outer delayloop
;
enddly	RETURN
	END

Now derive a stimulus file for the above program.

Updated 20.06.07 ML