Originally Posted by blueroomelectronics

After reading Pommies excellent post on a 2 key roll-over keyboard with RS232 out, I thought it would be interesting to post a link to vertical counters for keyboard denouncing as opposed to time delay denouncing.
Vertical Counters with a PIC

I've yet to use the vertical method myself but thought it would make good food for thought.

I hate time delay debounce, vertical counters is time delay debounce and the worst kind, the kind that has a delay after the button is pressed. The beauty of the way I do debounce is that when a button is pressed it is immediately acted upon and not after some debounce delay. I have buttons in my car that are debounced using a delay, I can press them fast enough that they don't register. You can't do that with the code I posted. clicky.

For anyone not familiar with the method I use, it is rather simple, if the button wasn't pressed 10mS ago and is now pressed then it's registered as a new key press. It effectively detects rising edges.

BTW, I've never denounced anyone.

Mike.

Variations of Scott Dattalo's method of using vertical counters as eight independent debounce timers provide amazing and extremely versatile parallel switch debounce/management solutions. The time and effort it takes to understand vertical counters and parallel switch state logic is a good investment.

For example, here's Scott's basic 2 bit vertical counter debounce code with a few additional instructions for parallel switch state management that provides a pretty complete interrupt driven debounce solution for up to eight switches using only 14 words of program memory;

Code:

;
; Scott Dattalo's debounce method for up to 8 switches uses a 2
; bit vertical counter as eight independent debounce timers.  A
; few instructions have been added for parallel switch state
; management.
;
; a switch is "debounced" (both press and release states) when it
; has been sampled four times at the same state spanning a 24 msec
; period (using 8 msec sampling intervals).
;
; vcbit1 ^= vcbit0;             // inc counters (unconditionally)
; vcbit0 = ~vcbit0;             //
; vcmask = ~portb ^ slatch;     // changes (press or release)
; vcbit0 &= vcmask;             // clear inactive counters
; vcbit1 &= vcmask;             //
; vcmask = ~vcmask;             // check for timed-out counters
; vcmask |= vcbit0;             //
; vcmask |= vcbit1;             //
; vcmask = ~vcmask;             // any 1's are timed-out counters
; slatch ^= vcmask;             // update debounced switch state
; vcmask &= slatch;             // filter out "new release" bits
; sflags ^= vcmask;             // update switch flags for Main
;
test_0                          ; 14 words
        movf    vcbit0,W        ; inc counters unconditionally    |B0
        xorwf   vcbit1,F        ; inc bit 1 vertical counter      |B0
        comf    vcbit0,F        ; inc bit 0 vertical counter      |B0
        comf    PORTB,W         ; sample active low switches      |B0
        xorwf   slatch,W        ; changes (press or release)      |B0
        andwf   vcbit0,F        ; clear inactive bit 0 counters   |B0
        andwf   vcbit1,F        ; clear inactive bit 1 counters   |B0
        xorlw   0xFF            ; check for timed-out counters    |B0
        iorwf   vcbit0,W        ;                                 |B0
        iorwf   vcbit1,W        ; any '0' is a timed-out counter  |B0
        xorlw   0xFF            ; any '1' is a new press/release  |B0
        xorwf   slatch,F        ; update debounced switch state   |B0
        andwf   slatch,W        ; filter out "new release" bits   |B0
;       skpz                    ; a "new press"? no, skip, else   |B0
;       bsf     beeper,5        ; task a "new press" beep         |B0
        xorwf   sflags,F        ; update switch flags for Main    |B0
;

This routine filters out the "new release" switch state and only passes on the "new press" switch state. Your Main program simply needs to test and clear a switch flag bit in the sflags variable for "momentary" type switches, or simply test a switch flag bit for momentary switches that you want to emulate a "toggle" switch (press the switch to toggle the flag bit from on-to-off or from off-to-on).

I should also mention that since the slatch variable contains the real-time debounced switch state (plus debounce delay), it's relatively easy to implement "repeat" key functionality on-the-fly as needed in Main using this variable. There are examples of this in my Charlie Clock in the Projects Forum where I use "repeat" key capability for the <up> and <down> arrow keys to adjust the hours, minutes, or seconds display group only when in "Set" mode. When in "Display" or "Run" mode the <up> and <down> arrow keys are used to select the display (Clk, Tmr, Cal, or display off) and the keys do not "repeat".

Have fun guys.

Mike

Originally Posted by Pommie

...vertical counters is time delay debounce and the worst kind, the kind that has a delay after the button is pressed. The beauty of the way I do debounce is that when a button is pressed it is immediately acted upon and not after some debounce delay.

So, you're not accounting for noise that could false trigger? I posed a similar solution a few years back (I think on the Piclist) and was told the delay was needed as part of that filtering process. In reality, I'm not sure how much of an issue it is.

Dave
(new guy, by the way. Hi everyone!)

Originally Posted by dave_b

So, you're not accounting for noise that could false trigger? I posed a similar solution a few years back (I think on the Piclist) and was told the delay was needed as part of that filtering process. In reality, I'm not sure how much of an issue it is.

Dave
(new guy, by the way. Hi everyone!)

Hi Dave,

The way I deal with debounce is by only reading the keys every 10mS. I keep a copy of the previous reading and if the new reading says pressed and the old says released then a new key press has occurred. The only way key bounce can cause a double read is if the bounce last longer than 20mS which does not occur with anything better than a paper clip and thumb tack.

Nearly forgot, welcome to the forum.

Mike.