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On this page ...
Overview
How to connect the LCD to you Basic Stamp II Below you will find two tables, both containing identical data, except the first one is the proper way to display the connection. The second table is for the impatient and more experienced user showing what to connect to what. Make these connections:
The quick and dirty notation for the impatient (like myself):
Note: the pin out is based on Jon's LCDDEMO1.BAS. However this did not work for me due to two little mistakes in the LCD connections (however: without it it would have taken me ages!).
To make the ports work properly we need a little Pbasic code: Init: DirL = %00111111 ' set (lower 8) pins 0-5 as outputs
Outs = $0000 ' clear the pins
Getting Control - Sending text OK, so now we hooked to LCD up to our Basic Stamp 2. How do we control a parallel controlled LCD panel by using only 6 wires? The answer is actually pretty simple (thanks to Jon's work): the LCD panel can be controlled using 8-bits or 4-bits. 4-bit mode is working identical to 8-bit mode mode, however we transmit the upper 4 bits and the lower 4 bits in sequence instead of 8 bits parallel. Practical example: Say we would like to send the character 'A' which is
in binary code: First we send the upper 4 bits called a nibble (now
this will be confusing when you start with it, but you'll get used to
it). Second we send the lower 4 bits. 0100 Which will result in a character 'A' on your LCD display. This all sounds pretty hard to do, but be assured. The Basic Stamp 2 has some neat routines that will help us with this task. Let's say that a character uses the space of one byte (=8 bits) and we define a variable for that purpose. In Pbasic that would like this: char VAR Byte ' character sent to LCD Here we define the variable ('var'-statement)
called 'char' of type 'Byte'. OutA = char.HIGHNIB ' output high nibble Similar, the next statement will output the lower 4 bits: OutA = char.LOWNIB ' output lower nibble To get read/write activity we just need to add a little additional code to get a pulse to the 'E'-pin of the LCD panel, which we connected to pin5 of the Basic Stamp 2, after sending the nibble. Once more Pbasic shows it's power. Sending a simple 'high' (=1) to pin5 is done with this little piece of: PULSOUT 5, 1 ' strobe the Edge Enable line To get the LCD to know that we are sending data (not
a instruction) we must raise the 'RS'-pin of the LCD high as well. Since
we leave RS high, you might wonder why we keep doing it, but that soon
will be clear once we implement a routine for sending instructions. HIGH 4 ' goto write-character mode That's it for sending characters. However that's not enough to get the display operational. See the next paragraph for sending instructions. Below you will find the gosub-routine for sending characters: ' =-=-=-=-=-=-=-=-=-=-=-= ' Write ASCII char to LCD ' =-=-=-=-=-=-=-=-=-=-=-= LCDwr: OutA = char.HIGHNIB ' output high nibble PULSOUT 5, 1 ' strobe the Enable line OutA = char.LOWNIB ' output low nibble PULSOUT 5, 1 HIGH 4 ' return to character mode RETURN Getting Control - Sending instructions Sending instructions is basically the same as sending
characters. The only difference is that pin4 (RS of the LCD) should be
LOW instead of HIGH. The LCD panel uses this to distinct between text
and instructions. LOW 4 ' enter command mode Next step is to send the actual instruction. The instruction however is basically a character, so we can use our 'LCDsendchar' routine to send the instruction. Our gosub-routine could look like this: ' =-=-=-=-=-=-=-=-=-=-=-=- ' Write instruction to LCD ' =-=-=-=-=-=-=-=-=-=-=-=- LCDcmd: LOW RS ' enter command mode LCDsendchar ' then write the character
' LCD control characters ' ClrLCD CON %00000001 ' clear the LCD CrsrHm CON $00000010 ' move cursor to home position CrsrLf CON $00010000 ' move cursor left CrsrRt CON $00010100 ' move cursor right DispLf CON $00011000 ' shift displayed chars left DispRt CON $00011100 ' shift displayed chars right DDRam CON $10000000 ' Display Data RAM control So how do we use the instructions? Well, having defined some constants, an gosub-routines for writing characters and one instructions, things should work pretty easy. Practical example: Let's clear the display: Char = ClrLCD GOSUB LCDcmd Or let's move the cursor to the left: Char = CrsrLf GOSUB LCDcmd You might think that's it, but it isn't. Before we can do ANYTHING with the LCD display, we need to initialize it. Generic Control - Initializing the LCD The gosub-routines we just defined are very useful for this particular task: initializing the LCD display. We need to keep in mind that the display must be initialized in 4-bit mode. Using the reference manual of Hitachi, this should be the way to do it:
* = Use instructions table to
customize to your needs
LCDini: pause 50 ' Wait for LCD init ' ================================= ' STANDARD HITACHI 44780 4-BIT INIT ' ================================= char=%00000011 ' Set 8-bit mode (1) GOSUB LCDcmd char=%00000011 ' Set 8-bit mode (2) GOSUB LCDcmd char=%00000011 ' Set 8-bit mode (3) GOSUB LCDcmd char=%00000010 ' Set 4-bit mode GOSUB LCDcmd char=%00101111 ' Set duty cycle 11xx = 5x11 matrix GOSUB LCDcmd ' 10xx = 5x8 matric char=%00000000 ' Display control mode GOSUB LCDcmd char=%00001000 ' Set display OFF, cursor OFF, blink OFF GOSUB LCDcmd char=%00000000 ' Display control mode GOSUB LCDcmd char=%00001111 ' Set display ON, cursor ON, blink ON GOSUB LCDcmd ' 11CB -> C=1 cursor on, B=1 blink on char=%00000000 ' Entry control mode GOSUB LCDcmd char=%00000110 ' Set cursor right, no display shift GOSUB LCDcmd ' 01IS -> I=1 cursor right, S=1 shift display char = ClrLCD ' Clear LCD GOSUB LCDcmd The official LCD FAQ and Hitachi documentation mention al lot about the execution timing. Using the Basic Stamp 2 that appears not be an issue. OPTREX DMC2034 and DMC50400 - A 4x20 LCD layout I used both these Optrex 4x20 LCD display-types, which both use the Hitachi 44780 controller. The pin-layout of this display is basic for all Hitachi-based LCD displays. The character layout of the display is pretty basic for all 4x20 displays. For 4x20 LCD's you will generally find two types of layout, more recent displays support the layout you find below.
When filling the character positions, starting in the upper left corner, the display will be filled starting in the upper left corner and end in the lower right corner. Older 4x20 LCD displays, like the Optrex I'm using, have different line layout:
Notice that the lines 1 and 3 follow each other. Line 2 is followed by line 4. So basically when filling all character positions, the lines will be filed in this order: line 1, line 3, line 2 and finally line 4. This makes it a bit harder to control the position of the cursor on the LCD display. You can take a look at this gosub-routine I wrote (see Example 3 for a demo) which uses the cursor repositioning functionality of the display: ' ============================
' Write char at position (X,Y)
' ============================
' Usage:
' X=10 ' horizontal position or column (X)
' Y=2 ' vertical position or line (Y)
' char="A" ' character to write
' GOSUB LCDpos ' position cursor and write char
'
LCDpos:
char2=char ' Save char
char=CrsrHm ' Set cursor to home location
GOSUB LCDcmd
counter=%00000000 ' Reset counter (=position 0)
IF Y=1 THEN done ' 4x20: row1 starts at position 0
IF Y=2 THEN pos_row2
IF Y=3 THEN pos_row3
IF Y=4 THEN pos_row4
pos_row2: ' 4x20: row2 starts at position 64
counter=%01000000
GOTO position
pos_row3: ' 4x20: row3 starts at position 20
counter=%00010100
GOTO position
pos_row4: ' 4x20: row4 starts at position 84
counter=%01010100
GOTO position
position:
counter=counter+X-1 ' Add X to Y position minus 1 (pos 1 = 0)
char=%10000000+counter
GOSUB LCDcmd
done: char=char2 ' restore old char
GOSUB LCDwr ' and write it
RETURN
Hitachi 44780 Pin layout Hitachi based LCD display have a very common connector to the outer world:
This is an adapted version of Jon Williams (http://members.aol.com/jonwms) his LCDDEMO1.BS2. It basically initializes the LCD display and sends a text to the display over and over again (download here): ' -----[ Constants ]-------------------------------------------------------
' Ports used
RS CON 4 ' Register Select (1 = char)
E CON 5 ' LCD Enable pin (1 = enabled)
' LCD control characters
'
ClrLCD CON $01 ' clear the LCD
CrsrHm CON $02 ' move cursor to home position
CrsrLf CON $10 ' move cursor left
CrsrRt CON $14 ' move cursor right
DispLf CON $18 ' shift displayed chars left
DispRt CON $1C ' shift displayed chars right
DDRam CON $80 ' Display Data RAM control
' -----[ Variables ]-------------------------------------------------------
'
char VAR Byte ' character sent to LCD
index VAR Byte ' loop counter
' -----[ EEPROM Data ]-----------------------------------------------------
'
Msg DATA "BASIC Stamp 2 LCD in action" ' preload message
' -----[ Initialization ]--------------------------------------------------
'
Init: DirL = %00111111 ' set pins 0-5 as outputs
Outs = $0000 ' clear the pins
' Initialize the LCD (Hitachi HD44780 controller)
'
LCDinit: pause 500 ' Wait for LCD init
' =================================
' STANDARD HITACHI 44780 4-BIT INIT
' =================================
char=%00000011 ' Set 8-bit mode (1)
GOSUB LCDcmd
char=%00000011 ' Set 8-bit mode (2)
GOSUB LCDcmd
char=%00000011 ' Set 8-bit mode (3)
GOSUB LCDcmd
char=%00000010 ' Set 4-bit mode
GOSUB LCDcmd
char=%00101111 ' Set duty cycle 11xx = 5x11 matrix
GOSUB LCDcmd ' 10xx = 5x8 matric
char=%00000000 ' Display control mode
GOSUB LCDcmd
char=%00001000 ' Set display OFF, cursor OFF, blink OFF
GOSUB LCDcmd
char=%00000000 ' Display control mode
GOSUB LCDcmd
char=%00001111 ' Set display ON, cursor ON, blink ON
GOSUB LCDcmd ' 11CB -> C=1 cursor on, B=1 blink on
char=%00000000 ' Entry control mode
GOSUB LCDcmd
char=%00000110 ' Set cursor right, no display shift
GOSUB LCDcmd ' 01IS -> I=1 cursor right, S=1 shift display
char = ClrLCD ' Clear LCD
GOSUB LCDcmd
' -----[ Main Code ]-------------------------------------------------------
'
Start:
FOR index = 0 TO 39
READ Msg + index, char ' get character from memory
GOSUB LCDwr ' write it to the LCD
NEXT
PAUSE 1000 ' wait 2 seconds char = ClrLCD ' clear the LCD
GOSUB LCDcmd
PAUSE 500
GOTO Start ' do it all over
' -----[ Subroutines ]-----------------------------------------------------
'
' Send command to the LCD
'
LCDcmd: LOW RS ' enter command mode
'
' Write ASCII char to LCD
'
LCDwr:
OutA = char.HIGHNIB ' output high nibble
PULSOUT E, 1 ' strobe the Enable line
OutA = char.LOWNIB ' output low nibble
PULSOUT E, 1
HIGH RS ' return to character mode
RETURN
In this example a gauge is running up and down using a routine to reposition the cursor on the display. ' -----[ Constants ]-------------------------------------------------------
' Ports used
RS CON 4 ' Register Select (1 = char)
E CON 5 ' LCD Enable pin (1 = enabled)
' LCD control characters
'
ClrLCD CON $01 ' clear the LCD
CrsrHm CON $02 ' move cursor to home position
CrsrLf CON $10 ' move cursor left
CrsrRt CON $14 ' move cursor right
DispLf CON $18 ' shift displayed chars left
DispRt CON $1C ' shift displayed chars right
DDRam CON $80 ' Display Data RAM control
' -----[ Variables ]-------------------------------------------------------
'
char VAR Byte ' character sent to LCD
char2 VAR Byte ' Duplicate character store
index VAR Byte ' loop counter
counter VAR Byte ' 2nd counter
X VAR Byte ' X position
Y VAR Byte ' Y position
'-----[ Initialization ]--------------------------------------------------
'
Init: DirL = %00111111 ' set pins 0-5 as outputs
Outs = $0000 ' clear the pins
'=================================
' STANDARD HITACHI 44780 4-BIT INIT
' =================================
LCDinit: pause 500 ' Wait for LCD init
char=%00000011 ' Set 8-bit mode (1)
GOSUB LCDcmd
char=%00000011 ' Set 8-bit mode (2)
GOSUB LCDcmd
char=%00000011 ' Set 8-bit mode (3)
GOSUB LCDcmd
char=%00000010 ' Set 4-bit mode
GOSUB LCDcmd
char=%00101111 ' Set duty cycle 11xx = 5x11 matrix
GOSUB LCDcmd ' 10xx = 5x8 matric
char=%00000000 ' Display control mode
GOSUB LCDcmd
char=%00001000 ' Set display OFF, cursor OFF, blink OFF
GOSUB LCDcmd
char=%00000000 ' Display control mode
GOSUB LCDcmd
char=%00001100 ' Set display ON, cursor ON, blink ON
GOSUB LCDcmd ' 11CB -> C=1 cursor on, B=1 blink on
char=%00000000 ' Entry control mode
GOSUB LCDcmd
char=%00000110 ' Set cursor right, no display shift
GOSUB LCDcmd ' 01IS -> I=1 cursor right, S=1 shift display
char = ClrLCD ' Clear LCD
GOSUB LCDcmd
PAUSE 500
'-----[ Main Code ]-------------------------------------------------------
'
Start:
Y=2
FOR X=6 TO 15
char="0"+X-6
GOSUB LCDPos
NEXT
start2:
Y=1
char=255
FOR X=6 to 15
GOSUB LCDPos
pause 50
NEXT
char=" "
FOR X=6 to 15
GOSUB LCDPos
pause 50
NEXT
goto start2
'-----[ Subroutines ]-----------------------------------------------------
This example is similar to the previous example with the difference to be found in the positioning routine, which is considerably faster in this demo. ' -----[ Constants ]-------------------------------------------------------
' ports used
RS CON 4 ' Register Select (1 = char)
E CON 5 ' LCD Enable pin (1 = enabled)
My mini BOE - Board Of Education Here you will find what I did to create a so called BOE (Board Of Education) for purposes like this (LCD testing). BOM - Bill Of Materials 1x DIL 40 chip socket First I mounted a regular chip-socket (DIL-40) which I cut into two pieces. This will be used as a mount connector for the OEM Basic Stamp 2 board. Next I soldered to other part of the DIL-40 (only 8 pins of them) upside down on the board, so it would function as a socket kind of thing. This socket I have numbered the pins of: pin 1 to 8 and wired them to the OEM Basic Stamp 2 socket. Next I wired the connections of the LCD panel to a connector that fit's the socket I created for the LCD hookup;
Pictures of this BOE can be found here. |
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