' =========================================================================
'   File....... SW21-EX14-Debounce.SXB
'   Purpose.... Simple digital clock with software multiplexing
'   Author..... (C) 2000 - 2005, Parallax, Inc.
'   E-mail..... support@parallax.com
'   Started.... 01 SEP 2005
'   Updated.... 23 MAR 2007 by TSaavik for SX28
' =========================================================================

' -----[ Program Description ]---------------------------------------------
' This program demonstrates the simultaneous debouncing of multiple inputs,
' as well as the detection of a button status change (0 -> 1) between
' scans.  Note that the value in "xBtns" is only valid immediately after
' the call to Get_Buttons.

'------{ Device Settings ]-------------------------------------------------

DEVICE 		SX28,TURBO,BANKS8,OSCHS3,SYNC,OPTIONX
FREQ            50_000_000
ID		"EX14-ADV"
IRC_CAL         IRC_SLOW

' -----[ I/O Definitions ]-------------------------------------------------

BtnBus          VAR     RB                     ' four inputs, pins 0 - 3

' -----[ Constants ]-------------------------------------------------------


' -----[ Variables ]-------------------------------------------------------

nBtns           VAR     Byte                     ' new buttons
oBtns           VAR     Byte                    ' old buttons
xBtns           VAR     Byte                     ' changed, 0 -> 1
idx             VAR     Byte                     ' loop counter
lowbit		VAR	Byte

' -----[ Initialization ]-------------------------------------------------
PROGRAM Start
watch nbtns, 4, UBIN
watch obtns, 4, UBIN
watch xbtns, 4, UBIN


' -----[Subs ]-------------------------------------------------------------

' -----[ Program Code ]----------------------------------------------------

Start:
  Tris_B = %00001111                            ' make 0-3 inputs
 
Main:
  DO
    GOSUB Get_Buttons                           ' get debounced inputs
    FOR idx = 0 TO 3                            ' loop through inputs
      'DEBUG CRSRXY, 0, idx
       lowbit = idx and $0f
      IF xBtns.lowbit = 1 THEN           ' changed? (0 -> 1)
        'DEBUG "Fire ", DEC (idx + 1)            ' yes, show
      ELSE
        'DEBUG ".", CLREOL
      ENDIF
    NEXT
    PAUSE 250
  LOOP


' -----[ Subroutines ]-----------------------------------------------------

Get_Buttons:
  nBtns = %1111                                 ' enable all four inputs
  FOR idx = 1 TO 5
    nBtns = nBtns & ~BtnBus                     ' test inputs
    PAUSE 5                                     ' delay between tests
  NEXT
  xBtns = nBtns ^ oBtns & nBtns                 ' look for 0 -> 1 changes
  oBtns = nBtns                                 ' save this scan
  RETURN