--- michael brown <spam-me@houston.rr.com> wrote:
> 
> The OPTION reg shouldn't have any effect whatsoever on your port change
> interrupts.  Chances are much more likely that you have left the
> watchdog running accidentally or have interrupts occurring while you are
> switched to bank1, but the ISR doesn't know it and it blindly smacks up
> the wrong registers.  Or the ISR switches back to bank0, but doesn't
> properly save/restore the context info causing the main level code
> suffer psychotic episodes.  Stuff like this won't always show up in
> simulations.
> 
> When you use port change ints, you have to read the port as well as
> clearing the RBIF flag.  Otherwise the interrupt will trigger again
> because a mismatch condition still exists against the magical hidden
> shadow reg that holds the original pin values.  You have to read the
> port before clearing the RBIF, or it will instantly change back to a 1
> causing the int to fire again as soon as you execute the RETFIE.  This
> reloads the magical hidden shadow reg.  ;-)  The simulator may not get
> this right, it wouldn't be the first thing it didn't "simulate".
> 

Thankz Michael! I tried swapping bsf/bcf INTCON,GIE for movwf INTCON & reading
PORTB. No diff. The only thing I've found so far that does make a diff - ie
causes the PIC (16F84) to stay asleep until interrrupted - is b7 (RBU') in the
OPTION_REG.

Hmm. OK, Pull up resistors - what //exactly// do they do or what are the
pros/cons of having them enabled/disabled? And how could it possibly affect the
interrupts?

And I thought I had a handle on all this  ... :(

Here's the cut-down code if interested. The context-saving is handled by MACROS
- they're basically the routines Mike Predko gave in his book.

Debbie


  PAGE
         org       0x00
start    goto      main

         org       0x04  
intrpt:   
         goto      alert
         goto      main         ;Catches any errors. We hope!
 
<Subroutines in here.>

main:    
      <Config the Ports>
  
setint:
        BANK_1
        movlw    b'00011111'     ; Works if RBU' is cleared.
                                 ;b7 - RBPU' = 1 => Pull-ups disabled, 0 =>
enabled
                                 
        movwf    OPTION_REG
        BANK_0
        PAGE_0
        movlw    b'00011000'     ;Disable interrupts for now. GIE=0
        movwf    INTCON        

        <Switch on LEDs & Stuff>
loop:
        call    power_off
        <Do stuff>
                                ;Michael Brown's trick  ---> read the port 1st
        movlw   b'11111000'
        andwf   INTCON,f        ;Clear the flag bits in INTCON
        movf    PORTB,w         ;Read PORTB and then
        bsf     INTCON,GIE      ;Enable the interrupt
                            ;My orginal code
                            ;movlw   b'10011000'     ;Now enable the interrupts
                            ;movwf   INTCON
        nop
        sleep                   ;Shut down and wait 
        nop
        bcf     INTCON,GIE      ;Disable interrupts while doing housekeeping.
        goto    loop  


;The interrupt section ...

        include  "handler.asm"
alert:  
        call     intrpt_service
        bcf      INTCON,GIE            ;Disable interrupt temporarily
        goto     loop                  
        goto     main                  ;Catches errors .. we hope!
        end



	

	
		
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