' =========================================================================
'
'   File....... SW20-EX14-Debounce-Adv.BS2
'   Purpose.... Multi-input button scanning and debouncing
'   Author..... (C) 2000 - 2005, Parallax, Inc.
'   E-mail..... support@parallax.com
'   Started....
'   Updated.... 01 SEP 2005
'
'   {$STAMP BS2}
'   {$PBASIC 2.5}
'
' =========================================================================


' -----[ 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.


' -----[ I/O Definitions ]-------------------------------------------------

BtnBus          VAR     INA                     ' four inputs, pins 0 - 3


' -----[ Variables ]-------------------------------------------------------

nBtns           VAR     Nib                     ' new buttons
oBtns           VAR     Nib                     ' old buttons
xBtns           VAR     Nib                     ' changed, 0 -> 1
idx             VAR     Nib                     ' loop counter


' -----[ Program Code ]----------------------------------------------------

Main:
  DO
    GOSUB Get_Buttons                           ' get debounced inputs
    FOR idx = 0 TO 3                            ' loop through inputs
      DEBUG CRSRXY, 0, idx
      IF (xBtns.LOWBIT(idx) = 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 