' {$STAMP BS2p}
' {$PBASIC 2.5}
' Program Listing 22.1. BS2 Program to scan a 16-key matrix keypad
' Program: KEYP.BS2 (Scan a 16-key matrix keypad)
' This program shows how to scan a 4x4 matrix
' keypad using a BASIC Stamp II (BS2). A subroutine
' scans the keypad when it is called. On return, a
' flag bit (press) will contain a 1 if a key was
' pressed, and a nibble variable (key) will contain
' the key number (0-15). Once the program has
' responded to a key press, it must clear the
' press bit to prevent multiple actions triggered
' by the same key press. In a similar way, the
' keyScan subroutine uses another bit, db, to
' avoid responding to a key press until the key
' previously pressed has been released.

db  VAR Bit
press  VAR Bit
key  VAR Bit
row  VAR Nib
cols  VAR INB
userEntry VAR Nib(4)
fgh VAR Nib



again:
  GOSUB keyScan
  IF press = 0 THEN again
  DEBUG userEntry, HEX key, CR
  press = 0
  DEBUG userEntry
  FOR  fgh = 0 TO 2
      GOTO keyscan
      userEntry(fgh)= key
      press = 0
    DEBUG  DEC userEntry, CR
    NEXT
    RETURN


' ==================== KEYPAD SUBROUTINE ====================
' This code scans a 0 across the row connections of the keypad,
' then looks at the column nibble to see if that 0 has shown up
' on any of those bits. If the column bits are all 1s, then
' no key is pressed. If a column bit is 0, then a key is pressed
' at the intersection of the current row and that column.
keyScan:
FOR row = 0 TO 3   ' Scan rows one at a time.
LOW row    ' Output a 0 on current row.
  key = ~cols    ' Get the inverted state of column bits.
  key = NCD key   ' Convert to bit # + 1 with NCD.
  IF key <> 0 THEN push  ' No high on cols? No key pressed.
  INPUT row    ' Disconnect output on row.
NEXT     ' Try the next row.

db = 0      ' Reset the debounce bit.
RETURN

push:
  IF press = 1 THEN done  ' Already responded to this press, so done.
  db = 1: press = 1   ' Set debounce and keypress flags.
  key = (key-1)+(row*4)  ' Add column (0-3) to row x 4 (0,4,8,12).

' Key now contains 0-15, mapped to this arrangement:
' 0 1 2 3
' 4 5 6 7
' 8 9 10 11
' 12 13 14 15
' A lookup table is translates this to match the actual
' markings on the key caps.
  LOOKUP key,[1,2,3,10,4,5,6,11,7,8,9,12,14,0,15,13],key

done:
  INPUT row    ' Disconnect output on row.
RETURN