I wrote a simple program with MPLAB for my PIC18F252.
Program:
CONFIG WDT = OFF ; DISABLE WATCH DOG TIMER
CONFIG OSC = HS ; USE CRYSTAL
org 0 ; START CODE AT 0
START:
CLRF TRISA
CLRF TRISB
CLRF PORTA
CLRF PORTB
MAINLOOP
MOVLW B'11111111'
MOVWF PORTB ; MAKE ALL PINS 1(HIGH)
MOVLW B'11111111'
MOVWF PORTA ; MAKE ALL PINS 1(HIGH)
GOTO MAINLOOP
END
From this program, it should make all the pins in porta and portb high. So, if i connect and led to any of these pins (postive to pin, negative to ground) it should light up. However , it does not work for pin RA4 and does not work for RB5, RB6 and RB7. What could be the problem? Thanks.