On Wed, 12 Jun 1996, Martin J. Maney wrote:

> On Wed, 12 Jun 1996, Neil Gandler wrote:
>
> > On Tue, 11 Jun 1996, Martin J. Maney wrote:
> > > There's the work-around described in the datasheet (this has been in
> > > there for at least some of the 16Cxx parts for a while):
> > >
> > >   "The interrupt on change feature is recommended for wake-up on key
> > >    depression operation and operations where PORTB is used only for the
> > >    interrupt on change feature.  Polling of PORTB is not recommended
> > >    while using the interrupt on change feature."
> > >
> >
> >  So are you saying that if someone was to use a pin on port B with
> > the interrupt on change, that the rest of the ports pins shouldnt be
> > used for any other application?
> > I don't quite understadn what you meant.
>
> No, you've got it, near enough.  As John has explained (and given a nice
> example of its intended use), this really isn't of much use as a general
> interrupt source as you might expect in a general purpose machine.
>
> About all I can think of to add is the observation that even if you can
> afford to "waste" the rest of PORTB this probably can't be made entirely
> reliable for more general use.  The catch is that you HAVE to read the
> port in order to clear the interrupt that has occured, and that read can
> cause another interrupt to be missed.  Not very often, perhaps, but if
> you can't afford to miss the change...  (and, I tend to think, if you
> could afford to miss an occasional change, forget about the interrupt on
> change and just poll it from time to time and detect the changes
> yourself - as many pins, on whatever ports as you need.)
>

____

I just want to make sure I got this. If I have one input on PORT B
lets say PB7, with 3 leds on PB0-PB2. And I can't spare port B since
I am using the PIC16C61. If I use the interrupt on change feature and
I change the state of one of the LEDs that would trigger the state
change interrupt? Also an idea to prevent the ocassionaly miss of a
switch. Just make sure the keys are well debounced with a small delay.
The interrupt routine lasts perhaps for less than 1ms ( unless your
code is huge), I don't know how many people can repeatedly press
a button every millisecond.

        Neil Gandler