$regfile = "2313def.dat"
$crystal = 4000000

'I2C lines
Config Sda = Portd.5
Config Scl = Portd.4
'default I2C speed
Config I2cdelay = 10
'LED on this pin
Config Pind.6 = Output
'Int from PCF8574 to Int0 pin
Config Pind.2 = Input
Config Int0 = Falling

Const Pcf8574write = &H40
Const Pcf8574read = &H41
'Mask for reading columns and rows state
Const Columnsmask = &B11110000
Const Rowsmask = &B00001111
'Keyboard debounce time
Const Debouncetime = 150
Const Keystringlength = 10
Const Wtime = 100

Dim Pcf8574input As Byte
Dim Keycoderow As Byte
Dim Keycodecol As Byte
Dim Keycode As Byte
Dim Keychar As String * 1
Dim Keystring As String * Keystringlength
Dim Keycharpos As Byte
Dim Endofstring As Bit

Cls

On Int0 Pcfint

'Set PCF8574A to input, masked pins high (pull-up)
I2cstart
I2cwbyte Pcf8574write
I2cwbyte Columnsmask
I2cstop

Enable Interrupts
Enable Int0

Do
  Endofstring = 0
  Keystring = Space(keystringlength)
  Keycharpos = 0
  Cls
  Lcd "? "
  While Endofstring = 0
    Set Portd.6
    Waitms Wtime
    Reset Portd.6
    Waitms Wtime
  Wend
  Lowerline
  Lcd "S " ; Keystring
  Wait 1
Loop

'PCF8574 interrupt routine
Pcfint:
  'read the input pins
  I2cstart
  I2cwbyte Pcf8574read
  I2crbyte Keycodecol , Nack
  I2cstop
  'shift upper nibble to lower nibble
  Shift Keycodecol , Right , 4
  'switch column and row input/output state
  I2cstart
  I2cwbyte Pcf8574write
  I2cwbyte Rowsmask
  I2cstop
  'read the input pins
  I2cstart
  I2cwbyte Pcf8574read
  I2crbyte Keycoderow , Nack
  I2cstop
  'Cls
  'Lcd Bin(keycodecol) ; Bin(keycodecol)
  'switch column and row input/output state back
  I2cstart
  I2cwbyte Pcf8574write
  I2cwbyte Columnsmask
  I2cstop
  Select Case Keycoderow
    Case 7 : Keycode = 0
    Case 11 : Keycode = 4
    Case 13 : Keycode = 8
    Case 14 : Keycode = 12
    Case Else : Keycode = 99
  End Select
  'make final keycode from portb pins read
  Select Case Keycodecol
    Case 7 : Keycode = Keycode + 0
    Case 11 : Keycode = Keycode + 1
    Case 13 : Keycode = Keycode + 2
    Case 14 : Keycode = Keycode + 3
    Case Else : Keycode = Keycode + 99
  End Select
  'illegal keycode from bounce effects
  If Keycode > 15 Then Keycode = 16
  'Cls
  'Lcd Keycoderow ; " " ; Keycodecol ; " " ; Keycode
  Keychar = Lookupstr(keycode , Keycodes)
  If Keychar <> "?" Then
    Lcd Keychar
    If Keychar <> "E" Then
      Keycharpos = Keycharpos + 1
      Mid(keystring , Keycharpos , 1) = Keychar
      Print "keystring: " ; Keystring
      If Keycharpos = 16 Then
        Endofstring = 1
      Else
        Endofstring = 0
      End If
    Else
      Endofstring = 1
    End If
  End If
  Waitms Debouncetime
  Gifr = 64
Return

End

Keycodes:
Data "1" , "2" , "3" , "A" , "4" , "5" , "6" , "B" ,
Data "7" , "8" , "9" , "C" , "R" , "0" , "E" , "D" , "?"