' Name        : LCD_BIT_BANG.pbp
' Compiler    : PICBASIC PRO Compiler 2.6
' Assembler   : PM or MPASM
' Target PIC  : 40-pin 16F877A, 18F452 or similar
' Hardware    : LAB-X1 Experimenter Board
' Oscillator  : 4MHz external crystal
' Keywords    : LOOKUP
' Description : PICBASIC PRO program to manually operate (without LCDOUT)
' an LCD in 4-bit mode with the PIC16F877A and LAB-X1.
'

' Alias LCD connections - any output pin can be used
LCD_DB4 Var PORTD.4  ' LCD data bit 4
LCD_DB5 Var PORTD.5  ' LCD data bit 5
LCD_DB6 Var PORTD.6  ' LCD data bit 6
LCD_DB7 Var PORTD.7  ' LCD data bit 7
LCD_RS  Var PORTE.0  ' LCD register select
LCD_E   Var PORTE.1  ' LCD enable
LCD_RW  Var PORTE.2  ' LCD read/write

c Var Byte           ' Variable to store character to send to the LCD
i Var Byte           ' Loop counter

   ADCON1 = 7        ' Set PIC16F877A analog pins to digital
   Pause 500         ' Wait for the LCD to power up
   Gosub lcdinit     ' Initialize the LCD

mainloop:
   Gosub lcdclr      ' Clear the LCD screen
   For i = 0 to 4    ' Send string to the LCD one letter at a time
     Lookup i, ["Hello"], c  ' Get letter from string to variable c
     Gosub lcddata   ' Send data in c to the LCD
   Next i
   Pause 500         ' Wait .5 second

   Gosub lcdclr      ' Clear the LCD screen
   c = $c0           ' Move to second line of display
   gosub lcdcom      ' Send command in c to the LCD
   For i = 0 to 4    ' Send string to the LCD one letter at a time
     Lookup i, ["World"], c  ' Get letter from string to variable c
     Gosub lcddata   ' Send data in c to the LCD
   Next i
   Pause 500         ' Wait .5 second
   Goto mainloop     ' Do it forever

' Subroutine to write the lower nibble to the LCD
lcdlower:
   LCD_E = 1         ' Enabled
   LCD_DB4 = c.0     ' Write bit 0 to the LCD
   LCD_DB5 = c.1     ' Write bit 1 to the LCD
   LCD_DB6 = c.2     ' Write bit 2 to the LCD
   LCD_DB7 = c.3     ' Write bit 3 to the LCD
   Pauseus 1         ' Enable for at least 1us
   LCD_E = 0         ' Not enabled
   Return
 
' Subroutine to write the upper nibble to the LCD
lcdupper:
   LCD_E = 1         ' Enabled
   LCD_DB4 = c.4     ' Write bit 4 to the LCD
   LCD_DB5 = c.5     ' Write bit 5 to the LCD
   LCD_DB6 = c.6     ' Write bit 6 to the LCD
   LCD_DB7 = c.7     ' Write bit 7 to the LCD
   Pauseus 1         ' Enable for at least 1us
   LCD_E = 0         ' Not enabled
   Return

' Subroutine to clear the LCD screen
lcdclr:
   c = 1             ' Set c to clear command and fall through to lcdcom

' Subroutine to send a command to the LCD
lcdcom:
   LCD_RS = 0        ' Set RS to command
   Gosub lcdupper    ' Write upper nibble to the LCD
   Gosub lcdlower    ' Write lower nibble to the LCD
   Pause 2           ' Wait command delay time, 2ms
   Return

' Subroutine to send data to the LCD
lcddata:
   LCD_RS = 1        ' Set RS to data
   Gosub lcdupper    ' Write upper nibble to the LCD
   Gosub lcdlower    ' Write lower nibble to the LCD
   Pauseus 50        ' Wait data delay time, 50us
   Return

' Subroutine to initialize the LCD
lcdinit:
   Low LCD_E         ' Set all LCD I/O lines to output low
   Low LCD_RS
   Low LCD_RW
   Low LCD_DB4
   Low LCD_DB5
   Low LCD_DB6
   Low LCD_DB7

   Pauseus 15100     ' Wait at least 15ms
   c = $33           ' Initialize the LCD
   Gosub lcdupper    ' Send to upper nibble only
   Pauseus 4200      ' Wait at least 4.1ms   
   c = $33           ' Send it again
   Gosub lcdupper    ' Send to upper nibble only
   Pauseus 100       ' Wait at least 100us
   c = $22           ' Put the LCD into 4 bit mode
   Gosub lcdupper    ' Send to upper nibble only
   c = $28           ' 4 bit mode, 2 lines, 5x7 font
   Gosub lcdcom      ' Send command in c to the LCD
   c = $0c           ' LCD display on, no cursor, no blink
   Gosub lcdcom      ' Send command in c to the LCD
   c = $01           ' Clear screen
   Gosub lcdcom      ' Send command in c to the LCD
   c = $06           ' LCD entry mode set, increment, no shift
   Goto lcdcom       ' Send command in c to the LCD and return

   End