<x-flowed>At 03:22 PM 2/16/00 -0600, Scott wrote:
> > ;copyright 1999 by robert a labudde, all rights reserved
>
>If you copy right it, you gotta make it the fastest. Right? :)

Wrong! Simply the best ...

Cycles don't matter for sure in a 20 ms debounce routine. I also usually
have program memory 'to burn' (good pun, huh?), so a few bytes don't count
either. Mostly my criteria are flexibility and clarity.

I copyright everything as a matter of course. Most people don't know that
the author owns the copyright even without the comment. You just have to
notify the user before taking legal action.

> > Debounce:
> >       movf   DEBOUNCE_PORT,w     ;get current port value
> >       andlw  DEBOUNCE_MASK       ;strip desired bits only
> >       xorwf  DEBOUNCE_OLD,w      ;find still changed bits
> >       andwf  DEBOUNCE_BITS,f     ;keep only changed ones
> >       xorlw  h'ff'               ;complement w
> >       andwf  DEBOUNCE_OLD,w      ;find unchanged bits
> >       iorwf  DEBOUNCE_BITS,f     ;merge with debounced
> >       return
>
>Where does DEBOUNCE_OLD get updated?

Whoops! I wrote this routine in Nov. 1999 based on a QuickBasic test
program version. I haven't used the routine yet in a PIC. I apparently
dropped a line in transcription. I've attached a corrected version of the
ASM, and also a copy of the QuickBasic program to show how I test logic and
math programs. It works great, and it's interactive.

I haven't got around to checking your modifications yet, but they look
interesting. The chief advantages seem to be slightly shorter code. What's
important to me, though, is that the steps mimic my thinking, so I can
eventually debug or change it. If it's too tricky, it may result in errors
at the boundary conditions.

Thanks for the critique.

</x-flowed>
'11.30.99 18.30  DEBOUNCE.BAS
'copyright 1999 by robert a labudde, all rights reserved
'debounce 8 bit port in 7 instructions (PIC)
'NOTES: iDebounced will give debounced state. This will only be updated
'       if changed bits persist over 2 call cycles. If only occur on 1
'       cycle, then bits remain unchanged.
'       It is important that do not call loop more often than 2x the
'       required debounce time T.
'created: 11.30.99 by r.a. labudde
'changes:

        DEFINT I-N
DECLARE FUNCTION BinToAscii$ (iBin%)
        DEF fnhex2$ (i) = RIGHT$("00" + HEX$(i), 2)

        iPort = 0       'initial state
        iOld = iPort    'copy
        iDebounced = iPort      'debounced version
        iMask = &H3     'only first two bits

        t$ = "   PORT       W        OLD   DEBOUNCED"
        u$ = "\      \  \      \  \      \  \      \"

        CLS
        PRINT t$
        PRINT

InputLoop:  REM this loop would be executed every T/2 ms, where T is interval
        INPUT "iPort:     ", iPort
        iW = iPort      'tranfer to working register
        iW = (iW AND iMask)     'only relevant bits
        iW = (iW XOR iOld)      'find different bits
        iDebounced = (iW AND iDebounced)'set different bits
        iOld = (iW XOR iOld)    'flip changed bits
        iW = (iW XOR 255)       'complement changed bits = unchanged bits
        iW = (iW AND iOld)      'merge with iOld
        iDebounced = (iW OR iDebounced) 'merge with debounced

        PRINT USING u$; BinToAscii$(iPort); BinToAscii(iW); BinToAscii$(iOld); BinToAscii(iDebounced)
        GOTO InputLoop

        END

FUNCTION BinToAscii$ (iBin)
  a$ = ""
  iNum = iBin
  iDiv = 128
  FOR i = 8 TO 1 STEP -1
   iBit = iNum \ iDiv
   IF iBit = 1 THEN
     iNum = iNum - iBit * iDiv
     a$ = a$ + "1"
   ELSE
     a$ = a$ + "0"
   END IF
   iDiv = iDiv \ 2
  NEXT i
  BinToAscii$ = a$
END FUNCTION


;02.17.00 15.40 DEBOUNCE.ASM
;copyright 1999,2000 by robert a labudde, all rights reserved
;debounce routine for pic ucontroller
;created:   11.30.99 by r.a. labudde
;changes:   02.17.00 ral, fix DEBOUNCE_OLD update
;
;
;includes:

;----------------------------- CONSTANTS
; DEBOUNCE_PORT     = port to debounce
; DEBOUNCE_MASK     = and mask for bits in port

;----------------------------- VARIABLES
; DEBOUNCE_OLD      = register for old state
; DEBOUNCE_BITS     = latest debounced bits

;-----------------------------SUBROUTINES

;............   Initialize debounce variables (1x)

DebounceInit:
     movf   DEBOUNCE_PORT,w     ;get current port and
     andlw  DEBOUNCE_MASK       ;get only bits needed
     movwf  DEBOUNCE_OLD        ;save in old and
     movwf  DEBOUNCE_BITS       ;and debounced
     return

;............   Debounce routine @ 1/2 debounce interval. Call every T/2.

Debounce:
     movf   DEBOUNCE_PORT,w     ;get current port value
     andlw  DEBOUNCE_MASK       ;strip desired bits only
     xorwf  DEBOUNCE_OLD,w      ;find still changed bits
     andwf  DEBOUNCE_BITS,f     ;keep only changed ones
     xorwf  DEBOUNCE_OLD,f      ;complement changed bits in copy
     xorlw  h'ff'               ;complement changed bits & unchanged bits
     andwf  DEBOUNCE_OLD,w      ;merge with copy
     iorwf  DEBOUNCE_BITS,f     ;merge with debounced
     return

<x-flowed>================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causae scire"
================================================================
</x-flowed>