Interrupt Problem

[Kamikaze47]

I've set up a very basic program to experiment with interrupts on a 16F84 (ive basically just used the example interrupt code from the pbp manual)

This main program should loop forever until RB0/INT goes high (via a pushbutton), and the interrupt routine should trigger and turn on the LED, and then go back to the endless loop in the main program.

However, when I press the button, the LED comes on for about 2 seconds and then turns off again. So i checked to see if it was resetting by putting code at the beginning of the program that makes the LED flash on and off a few times.

Sure enough, when i pressed the button, the LED came on for 2 seconds and then flashed, so the program was reset for some reason. It even resets if i pull out the oscillator after pressing the button. Now this seems to point me towards thinking that the watchdog timer is going off, but i dont know why it would.

DEFINE  OSC     10              ' Oscillator = 10MHz
define  INTHAND int_handler     ' Define interrupt handler

INTEDG  VAR OPTION_REG.6        ' RB0 Interrupt edge select: 1=Rising Edge 0=Falling Edge
INTF    VAR INTCON.1            ' RB0 Interrupt flag
INTE    VAR INTCON.4            ' RB0 Interrupt enable
GIE     VAR INTCON.7            ' Global interrup enable

LED     var PORTB.1             ' LED on RB1

wsave   var byte $20 system     ' Variable for saving W Register on Interrupt
ssave   var byte bank0 system   ' Variable for saving STATUS Register on Interrupt
psave   var byte bank0 system   ' Variable for saving PCLATH Register on Interrupt
fsave   var byte bank0 system   ' Variable for saving FSR Register on Interrupt

HIGH LED                        ' Flash LED Twice
pause 50
low led
pause 50
high led
pause 50
low led

INTEDG=1                        ' RB0 Interrupt to Trigger on Rising Edge
INTF=0                          ' Enable RB0 Interrupt
INTE=1                          ' Enable RB0 Interrupt
GIE=1                           ' Global Interrupt Enable

loop: Goto loop                 ' Endless Loop


'-----------------------------------------------------------------------------'
' Interrupt Handler                                                           '
'-----------------------------------------------------------------------------'

asm
int_handler
    ; Save Resisters ;
    movwf   wsave               ; Save W Register into wsave
    swapf   STATUS,W            ; Save STATUS Register into ssave
    clrf    STATUS                  
    movwf   ssave              
    movf    PCLATH,W            ; Save PCLATH Register into psave
    movwf   psave
    movf    FSR,W               ; Save FSR Register into fsave
    movwf   fsave

    ; Interrupt Code ;
    bsf     _LED                ; Turn on LED

    ; Restore Resisters ;
    movf    fsave,W             ; Restore FSR Resister
    movwf   FSR                 
    movf    psave,W             ; Restore PCLATH Resister
    movwf   PCLATH
    swapf   ssave,W             ; Restore STATUS Resister
    movwf   STATUS
    swapf   wsave,F             ; Restore W Resister
    swapf   wsave,W
    retfie
endasm

[Ingvar]

If my memory serves me right i think that the line .......
loop: Goto loop ' Endless Loop
...... will not kick the watchdog. You probably need to insert atleast one statement between the label and the goto.

/Ingvar

[Kamikaze47]

Tried that... Didnt help im afraid...

It looks like its not even making it out of the interrupt routine, and just locking up and resetting at some point after it turns on the led.

[J_Brittian]

I think Ingvar's right. I'm not sure you're leaving any room for an interrupt to occur. Try it like this:

loop:
For y = 0 to 100
pause 1
Next y
Goto loop

[Kamikaze47]

well the interrupt is def occuring or the led wouldnt come on at all. an interrupt handled in assembly doesnt need "room" for it to occur. It will jump right to the interrupt handler no matter what the processor is doing at the time... but ill try what you suggest

*edit* just tried it and no change... when i press the button attached to the interrupt pin the led goes high for 2 secs and then the whole thing crashes and restarts

[J_Brittian]

I'm sorry. I just realized that. Do you reset you're interrupt flag somewhere? Should there be an Intf = 0 just before the retfie?