On Fri, 11 Feb 2000, Don McKenzie wrote:

> "Longley, Jason" wrote:
> >
> > Hi, has anyone got a Switch debounce routine for a PIC
> > 16C84?
> > I also require help on a routine that makes sure a switch
> > is fully on for about 1/4 of a second before reseting a
> > count register to 0 other wise the switch is overlooked
>
> have a look at:
> http://www.dontronics.com/see.html
> this covers most of the more common routines used by these micros.

After that, look here to see an extremely fast and efficient one:

http://www.dattalo.com/technical/software/pic/debounce.html

If you dig into the routine, you might be able to solve your 1/4 second
switch must stay down problem. 1/4 is a really long time; 250,000 uSec is
the way I prefer to look at. So you're probably going to want to sample at
a faster rate (than once every 250,000 uS) - 20 mS is not uncommon for
this application - and save intermediate samples. Since your looking for a
change of states over this period you can do something very simple like
this:

; first grab the initial (presumably debounced) state:

    movf  SW_PORT,w
    movwf initial_sw_state
    clrf  change_detected   ; assume no changes
...

then in the periodic routine sampling the switches:

; Read the switch and see if it has changed

    movf  SW_PORT,w           ;get the current state
    xorwf initial_sw_state,w  ;compare with initial state
    iorwf change_detect,f     ;save any changes

...


Then after the quarter second is up:

    btfsc  change_detect,MY_SWITCH_OF_INTEREST_BIT_POSITION
     goto  switch_changed_states

; fall through to here if the switch did not change states
; and clear the count register...



Scott