' =============================================================================
' Program..... LCD_595.bas
' Author...... Jon Williams (jonwms@aol.com)
' Copyright... Copyright (c) 1999 Jon Williams
'
' Started..... 22 OCT 1999
' Updated..... 19 NOV 1999
' =============================================================================


' -----[ Program Description ]-------------------------------------------------
'
' This BasicX module provides low-level support for connecting a
' character-based LCD to the BasicX through a 74x595 shift register.
'
' The connection is four-bit mode.  It is up to the user to connect proper
' power, ground and contrast connections.  It is not possible to read back
' from the LCD using this interface.
'
' Connections:
'   NC = Not Connected
'   PU = Pulled Up to +5V through 10K resistor
'
'  BX-24    74HC595   LCD       Notes
' -------   -------   -------   ---------------- 
'            1 NC
'            2         6 (E)
'            3         4 (RS)
'            4        11 (D4)
'            5        12 (D5)
'            6        13 (D6)
'            7        14 (D7)
'            8 GND 
'            9 NC 
'           10 PU
' Pin 20    11                  Shift clock
' Pin 18    12                  Output latch
'           13 GND 
' Pin 19    14                  Shift data 
'           15 NC
'           16 Vcc


' -----[ Revision History ]----------------------------------------------------
'
' 22 OCT 1999 : Ported from Parallax PBASIC
' 27 OCT 1999 : Fine-tuned
' 19 NOV 1999 : Updated docs; reconfigured for BX-24


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

Private Const LCD_clock As Byte = 20        ' pin connections to 74x595
Private Const LCD_data As Byte = 19
Private Const LCD_latch As Byte = 18


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

Public Sub LCDInit(ByVal multiLine As Byte)

  Dim temp As Byte

  Call PutPin(LCD_clock, bxOutputLow)       ' setup connection pins
  Call PutPin(LCD_data, bxOutputLow)
  Call PutPin(LCD_latch, bxOutputLow)

  Call Sleep(0.25)                          ' allow LCD to self-init
  Call LCDPutByte(&H3, LCDcmd)
  Call Sleep(0.006)
  Call LCDPutByte(&H3, LCDcmd)
  Call Sleep(0.002)
  Call LCDPutByte(&H3, LCDcmd)
  Call LCDPutByte(&H2, LCDcmd)              ' 4-bit interface
  If (multiLine = LCDMulti) Then
    Call LCDPutByte(&H28, LCDcmd)           ' multi-line mode
  End If
  Call LCDPutByte(&HC, LCDcmd)              ' disp on, crsr off, blink off
  Call LCDPutByte(&H6, LCDcmd)              ' inc crsr, no disp shift
  Call LCDPutByte(LCDclear, LCDcmd)         ' get ready to use

End Sub

' -----------------------------------------------------------------------------

Public Sub LCDPutByte(ByVal theByte As Byte, ByVal mode As Byte)

  Dim temp As Byte

  temp = theByte And &HF0                   ' grab the high nibble
  If mode = 1 Then                          ' set RS bit to mode
    temp = temp Or &H8
  Else
    temp = temp And &HF7
  End If
  temp = temp Or &H4                        ' blip the E line
  Call ShiftOut595(temp)
  temp = temp And &HFB
  Call ShiftOut595(temp)
  temp = theByte * 16                       ' grab the low nibble
  If mode = 1 Then                          ' set RS to mode
    temp = temp Or &H8
  Else
    temp = temp And &HF7
  End If
  temp = temp Or &H4                        ' blip the E line
  Call ShiftOut595(temp)
  temp = temp And &HFB
  Call ShiftOut595(temp)

End Sub

' -----------------------------------------------------------------------------

Private Sub ShiftOut595(ByVal theByte As Byte)

  ' Send data to LCD through 74x595 shift register

  Dim theBit As Byte
  Dim mask As Byte

  mask = bx10000000                         ' start with MSB

  Do
    theBit = (theByte And mask) \ mask      ' isolate the bit
    Call PutPin(LCD_data, theBit)           ' spit it out
    Call PulseOut(LCD_clock, 0.0001, 1)     ' clock the bit
    mask = mask \ 2                         ' shift mask bit right
  Loop While (mask > 0)
  Call PulseOut(LCD_latch, 0.0001, 1)       ' latch data into the 595

End Sub