This page will let you learn a very easy tutorial on interfacing alphanumeric LCD.I opted for interfacing LCD with parallel port using visual basic 6 programming.With ease of programming in graphical user interface environment and its event driven nature makes this project more innovative.Working with DLL files in visual basic is easy as compared to C++ for programming parallel port.Before staring with Visual Basic 6 programming one should be clear with the concepts of the parallel port.Refer this link
Parallel port tutorialLcd used here has HD44780u dot matrix lcd controller.
Connection Diagram:
Caution:Make sure that 5V and GND lines are properly connected otherwise you may end up in damaging parallel port.
If you want backlight than connect pin 15 of LCD to 5V and pin 16 of LCD to GND. By adjusting 10k resistor make pin 3 of LCD at 0V. If connection are proper you will see this after power on.
LCD Video
Pin Information of LCD:
Algorithm to send data to LCD:
1.Make R/W low
2.Make RS=0 ;if data byte is command
RS=1 ;if data byte is data (ASCII value)
3.Place data byte on data register
4.Pulse E (HIGH to LOW)
5.Repeat the steps to send another data byte
LCD Initialization:
This is the pit fall for beginners.Proper working of LCD depend on the how the LCD is initialized. We have to send few command bytes to initialize the lcd. Simple steps to initialize the LCD
1.Specify function set:
Send 38H for 8-bit,double line and 5x7 dot character format.
2.Display On-Off control:
Send 0FH for display and blink cursor on.
3.Entry mode set:
Send 06H for cursor in increment position and shift is invisible.
4. Clear display:
Send 01H to clear display and return cursor to home position.
NOTE:One must refer the datasheet of LCD to get the proper time delay and required sequence.
Major hurdle in accessing parallel port in Windows Xp is the knowledge of using inpout32 files.
Download : Driver files
Now save inpout32.dll and port.dll in system32 folder in windows directory.We will use certain subroutine provided by these dll files in our VB6 code.Open new project in VB6 and create the form as shown below.
Set the max length of two text boxes to 16.Create "Start" and "Clear" command button.Add visual basic code to form.
Visual Basic Code
Dim data As Variant
Private Sub Clear_Click()
LowRs
Out Val(&H378), Val(1) ' function to send data to parallel port
Enable
txtlcd1.Text = " " ' line 1 for LCD
txtlcd2.Text = " " ' line 2 for LCD
End Sub
Private Sub Start_Click()
Out Val(&H37A), Val(Inp(&H37A) And &HDF)
lcd_int
LCDWriteString txtlcd1.Text
next_line ' function to set cursor to second line
LCDWriteString txtlcd2.Text
End Sub
Sub LowRs()
Out Val(&H37A), Val(Inp(&H37A) Or &H8) ' Rs Low
End Sub
Sub LowEn()
Out Val(&H37A), Val(Inp(&H37A) Or &H1) ' En Low
End Sub
Sub HighRs()
Out Val(&H37A), Val(Inp(&H37A) And &HF7) ' Rs High
End Sub
Sub HighEn()
Out Val(&H37A), Val(Inp(&H37A) And &HFE) ' En High
End Sub
Sub lcd_write(data%)
HighRs
Out Val(&H378), Val(data)
Enable
End Sub
Sub next_line()
LowRs
Out Val(&H378), Val(&HC0)
Enable
End Sub
Sub lcd_int() 'subroutine to initialize LCD
LowRs
Out Val(&H378), Val(&H38)
Enable
LowRs
Out Val(&H378), Val(&HC)
Enable
LowRs
Out Val(&H378), Val(&H6)
Enable
LowRs
Out Val(&H378), Val(&H1)
Enable
End Sub
Sub Enable()
DELAYUS 20000
HighEn
DELAYUS 2000
LowEn
DELAYUS 2000
End Sub
' function to send ASCII character one by one to LCD
Public Sub LCDWriteString(ByVal OutStr As String)
Dim i As Integer 'write a string to LCD
For i = 1 To Len(OutStr)
lcd_write (Abs(Asc(Mid(OutStr, i, 1))))
Next i
End Sub
Now go to Project>Add Module .Select inpout4.bas and port.bas
Subroutine Out Val (&address),Val(data) and DELAYUS 2000 is available in inpout4.bas and port.bas respectively.
Running the Program:
1.Press F5 to run the program
2.Write the text you want to display on the LCD in the textboxes
3.Click "Start" command button.
4.You will see that the same text appears on LCD as shown in the textboxes.
5.To send other text click "Clear" command button and repeat the same procedure.
