Harry,

I don't understand that.  It worked for me perfectly when I programmed the 
chip after adding the extra code I spoke to you about.   I didn't have to 
add any extra steps to abate any RMW problems.
 Oh well, as long as it's working for you, that's the main thing.



                                                                             
            Regards,

                                                                             
                Jim

----- Original Message ----- 
From: "Harry H. Arends" <h.arends@home.nl>
To: "'Microcontroller discussion list - Public.'" <piclist@mit.edu>
Sent: Saturday, August 30, 2008 1:10 PM
Subject: RE: [PIC] No reaction using chanhe on interrupt


> Hi Matthew,
>
> Your spot on, after the changes from Jim it still ditnt work.
> I created some extra code in the main loop like this:
>
>    bsf     OUTPUT, 2
> Loop:
>    movf    OUTPUT,w
>    andlw   0x0F
>    movwf   PORTA
>    goto    Loop
>
> And that dit the trick. Thanks now i have to get the timing right.
>
> Harry
>
> -----Oorspronkelijk bericht-----
> Van: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] Namens 
> Matthew
> Miller
> Verzonden: zaterdag 30 augustus 2008 17:37
> Aan: Microcontroller discussion list - Public.
> Onderwerp: Re: [PIC] No reaction using chanhe on interrupt
>
> Hi Harry,
>
> On Sat, Aug 30, 2008 at 04:04:17PM +0200, Harry H. Arends wrote:
>> OK i added some more code but still the same result.
>>
>> Niether PORT becomes high
>
> Another possibly is that you're experiencing a read, modify, write issue.
> This is very common on the mid-range parts. I'll give you an example:
> Let's say that bits 0 and 1 on PORTA are outputs and you want to drive 
> them
> both high. Here is the code you might use:
>
>   banksel PORTA
>   bsf     PORTA, 0
>   bsf     PORTA, 1
>
> You may find that only output 1 is set high, while output 0 is still low.
> This is because the second bsf read the port value (and read low for bit
> 0!), set bit 1 high and then wrote the value back to PORTA. This is the 
> RMW
> issue.
>
> The way around this is to use a shadow register. It's a good idea to do 
> this
> on all 10,12, and 16 series parts. Here is how this is done:
>
>  banksel shadowa
>  bsf     shadowa, 0
>  bsf     shadowa, 1
>  movf    shadowa, W
>
>  banksel PORTA
>  movwf   PORTA
>
> It's a few more instructions, but is avoids the RMW problem. You could 
> also
> put this code in a macro.
>
> Good luck!      Matthew
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