put eather a software delay or a hardware delay by using a timing capacitor 
in parallel and a pullup resistor when querying for input on the interrupt 1 
millisecond is good enough delay.. If you go with the hardware solution you 
will need a an input pin assigned to the button that is schmitdt triggered 
as the rising time for the button pulse is greatly reduced..
the button may be springing... and producing unwanred pulses...

----- Original Message ----- 
From: "Dan Price" <danielsprice@gmail.com>
Newsgroups: gmane.comp.hardware.microcontrollers.pic
Sent: Thursday, September 14, 2006 2:08 PM
Subject: [PIC] Trouble with ANSEL and Interrupts


> Hi, I am new to MCU programming and working with a 16F690 on a
> PICKIT2.  I am working on a display consisting of about 60 LED's
> driven by several 8-bit shift and store registers.  The basic idea is
> to trigger various patterns that change at a momentary button press
> and operate at different loop speeds based on the value of a
> potentiometer.
>
> All was going great until I started trying to setup an Interrupt
> triggered by the momentary button.   First off I am coding in C
> becuase I work much faster than in asm; however, I have been hard
> pressed to find external interrupt code in C to use as examples.
> Most of what I've found is either in assembly or all about the
> internal timer based interuppts.  I have searched the web, I have a
> couple of Predko books and looked through books in my local book store
> without any luck so any resources that people can provide will be
> greatly appreciated.  That being said and my noob status established
> here is the problem:
>
> In order to get the interrupt event to work I have to set the ANSEL
> register.  I set this to 0 as I am only interested in triggering the
> interrupt.  All ports other than RA2 for the button interrupt are
> outputs and no analog stuff is necessary at this time.  With the ANSEL
> register set to zero my interrupt works perfectly and cycles through
> each display pattern as intended, but suddenly there is all kinds of
> noise on the LED's.  Each LED now flickers a small amount at all times
> during the various pattern routines.  Additionally, the patterns
> themselves are slightly corrupted with some bits shifting incorrectly.
> This corruption is consistent and not random.  I have tried messing
> around with a variety of different registers with no joy.  If I
> comment out the ANSEL entry this problem goes away.  Can someone
> please provide some suggestions, a bit more explanation on the ANSEL
> register and most importantly some good C based resources for
> externally driven interrupts? Thanks, Dan
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