Hi,

I need some help with some simple assembly. The code are provided below. My
questions are -

1.   I connect the pin RB1 directly to a LED and the RBO/INT to the ground.
I then switch on the power.
The LED does not light up until the RB0/INT pin is switch to Vcc ( interrupt
occurs ). This is correct.
Now, I switch the RB0/INT back to ground and reset the power supply. The
moment i reconnect the
supply, the LED lights up eventhough no interrupt occurs. Why is that so?
I found that if i disconnect the supply for a longer period of time, then
the operation is correct.
Does it have something to do with discharging?

2.   I configure RBO/INT as an interrupt pin and found that when i connect
this pin to an LED, it lights up.
I use a meter to measure the output voltage of the pin and it produce a
reading of 1.5V - 2.0V.
Why is this so? Is there a need to put some form of buffers or diodes on the
respective input/output
lines?

Can anyone provide some advice on interfacing the i/o pins of PIC with other
analog/digital circuits?

Thanks for any advice.

        org     0
        goto    MAIN

        org     4       ; Interrupt Service Routine
        goto    INTSER

MAIN    bank1
        movlw   B'00000000'
        movwf   TRISA
        movlw   B'00011101'
        movwf   TRISB
        bank0
        clrf    PORTA
        clrf    PORTB
        bank1
        bcf     OPTREG,RBPU
        bsf     OPTREG,INTEDG
        bcf     INTCON,INTF
        bsf     INTCON,INTE
        bsf     INTCON,GIE
LOOP    sleep                   ; let IRQ wake it up and determine functions
        nop
        nop
        nop
        goto    LOOP

; Only RB0/INT is considered, other interrupts are disabled.

INTSER  movwf   w_temp
        swapf   STATUS,W
        movwf   status_temp
        bcf     INTCON,INTF
        bank0
        bsf     PORTB,1         ;bring the phone off hook
ENDINT  swapf   status_temp,W
        movwf   STATUS
        swapf   w_temp,F
        swapf   w_temp,W
        retfie

END
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