AVR-Chat

A couple of years ago I ran into this with an 8051, and my solution
was to simply wait for 20ms. 

The initial button press would cause the interrupt routine to
activate. The micro would then wait for 20ms (doing other stuff in the
meantime of course!), and re-check the interrupt at the end. If the
interrupt was in the same state, then it was a legitimate button press
(and not induced noise/etc), and therefore the program should act
accordingly. Remember as well that when the button is released the
noise will be present as well, something that bit me on the posterior
before I took it into account. (Ouch! That took a little while to
find...."why the !@#$%^&@$^% isn't this $!%^%$@^ working?!?!?".)

You may also wish to consider some IC solutions out there, I think
(from a hazy memory) that Maxim/Dallas have a keypad decoder chip that
debounces and decodes the keypress for you, making life a heap easier.

Good luck.

Adam.

--- In AVR-Chat@yahoogroups.com, "Jim Wagner" <jim_d_wagner@...> wrote:
>
> Manne -
> 
> There is a big problem that everyone runs into when trying
> to sense switches with an interrupt. It is called "switch
> bounce". It happens fairly slowly compared to the speed of
> the micro. You get MANY interrupts every time the switch
> opens or closes. 
> 
> There are several ways to deal with this. One is to "poll"
> (that is, read) the port pin regularly (maybe once every
> 1ms or so). Make a little "debounce" counter in software
> and a bit to remember the LAST state read. Every time you
> make a poll, compare the current state to the last state.
> If it is the same, count 1. If not the same, put the new
> state into the last-state bit.  When the debounce counter
> reaches some convenient value (say 4 or 8), then the switch
> state is "stable" and you then do what ever else needs to
> be done (like increment your LED counter.
> 
> Jim
> 
> 
> On Sat, 17 Feb 2007 00:37:04 +0100 (CET)
>  "Manne Tallmarken" <mannet@...> wrote:
> > Hi all,
> > I am trying to make my first assembler program that
> > handles interrupts. On
> > PB[6:0] I have som leds and on PA[7:6] i have two
> > buttons. The leds goes
> > on with a logic one from the port and the buttons is in
> > tri-state when not
> > pushed and goes to logic zero when pushed.
> > I just trying to get a binary counter to show up on the
> > leds when i am
> > pushing the buttons but nothing happens.
> > Does anyone know what could be wrong?
> > Regards, Manne
> > 
> > Here is the code:
> > 
> > .include "tn26def.inc"
> > 
> > ; Interrupt service vectors
> > 
> > .org $0000
> >         rjmp Reset
> > .org IOPINSaddr
> >         rjmp IntPins
> > 
> > ; define registers
> > .def TIME=r16
> > .def TEMP=r17
> > 
> > ; define constants
> > .equ PORTB_IO=$7f       ; pb[6:0] = output
> > .equ PORTA_IO=$00       ; pa[7:0] = input
> > 
> > Reset:
> >         ldi     TEMP, RAMEND    ; set stack pointer to
> > RAMEND
> >         out     SP, TEMP        ; (SP is one byte on
> > attiny26)
> > 
> >         ldi TEMP, PORTB_IO
> >         out DDRB, TEMP
> >         ldi TEMP, $00           ; all lights off
> >         out PORTB, TEMP
> > 
> >         ldi TEMP, PORTA_IO
> >         out DDRA, TEMP
> >         ldi TEMP, (1<<PA3) + (1<<PA6) + (1<<PA7)
> >                ; enable
> > pullup resistors
> >         out PORTA, TEMP
> > 
> > 
> >         ; set up interrupts
> > 
> >         ldi TEMP, (1<<PCIE1)
> >         out GIMSK, TEMP ; enable individual interrupt
> > PCIE1 ( PB[7:4],
> > PA[7:6], PA3 )
> >         ldi TIME, $00   ; start from 0
> > 
> >         sei
> > 
> > loop:
> >         rjmp loop
> > 
> > 
> > IntPins:
> >         inc TIME
> >         out PORTB, TIME
> >         reti
> > 
> > 
> 
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