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Parallax Serial LCD
2 rows x 16 characters, Non-backlit, with Piezospeaker (#27976)
2 rows x 16 characters, Backlit, with Piezospeaker (#27977)
4 rows x 20 characters, Backlit, with Piezospeaker (#27979)
The Parallax Serial LCDs are very functional, low-cost liquid crystal displays that can be easily interfaced
to and controlled by a microcontroller using a I/O pin. The LCD displays provide basic text wrapping so
that your text looks correct on the display. Full control over all of their advanced LCD features allows you
to move the cursor anywhere on the display with a single instruction and turn the display on and off in
any configuration. They support visible ASCII characters Dec 32-127, and in addition you may define up
to eight of your own custom characters to display anywhere on the LCD.
NOTE: If your Serial LCD Display does not have a speaker on the back, use the specifications
and information in the Product Change Notice: Revision E and Earlier section on page 11.
Features
Clear 40-pixel characters (8 H x 5 W)
Supports ASCII DEC characters 32-127
Define up to eight custom characters
Automatic text wrapping
Single command cursor placement
Single command clears the display
Define up to eight custom characters
Select 2400, 9600, or 19,200 baud with switches on
the back of the device
Display type: STN, YG, positive transflective LCD
Adjustable contrast knob on the back of the device
YG LED for backlit model displays
Key Specifications
Power requirements:
o
o
Non-backlit: +5 VDC, 20 mA
Backlit: +5 VDC, 20 mA (light off), ~ 80 mA typical (light on)
Communication: Selectable asynchronous serial baud rates: 2400, 9600, 19200
Operating temperature: -4 to +158 °F (-20 to +70°C)
Dimensions: NOTE - Board and LCD size and style may vary
o
o
2x16: Approx. 1.42 x 3.15 in (36 x 80 mm)
4x20: Approx. 2.37 x 3.86 in (60.2 x 98.1 mm)
Copyright © Parallax Inc.
Parallax Serial LCDs (#27976, 27977, 27979)
v3.1 3/11/2013 Page 1 of 11
Quick-Start Circuit
The Serial LCDs should be powered from an external regulated 5 V power supply. Make sure the power
supply has an adequate current rating to power the Serial LCD and the BASIC Stamp, Propeller chip, or
whichever microcontroller and other devices you are using.
CAUTION
DO NOT PROVIDE A SIGNAL TO THE 'RX' PIN BEFORE APPLYING 5 VDC TO THE '5V' PIN.
Baud Rate Setup
After connecting the Serial LCD, you will need to select the baud rate at which you are going to send it
data. You have three choices: 2400, 9600, and 19,200 baud. To set the baud rate, move the dip switches
on the back of the LCD into the correct positions according to the table next to the switches, which is also
repeated below:
MODE
Test
2,400
9,600
19,200
SW1
OFF
ON
OFF
ON
SW2
OFF
OFF
ON
ON
As you can see from the table, there is also a fourth choice called Test. Use this Test mode to confirm
that the power and ground to the LCD are hooked up correctly before you send it any data. Move the dip
switches to the Test setting and turn on the power. The LCD display should turn on with the backlight on
(models 27977, 27979) and display the following text:
Parallax, Inc.
www.parallax.com
If you don’t see the text at first, try adjusting the LCD contrast by turning the pot labeled “Increase
Contrast” with a screwdriver. Turn it in the direction of the arrow to make the characters show up more
clearly. If you still don’t see the characters, go back and check your electrical connections and try again.
Once you’ve successfully completed test mode, move the dip switches to the correct positions to select
the baud rate you want to use for your application.
Copyright © Parallax Inc.
Parallax Serial LCDs (#27976, 27977, 27979)
v3.1 3/11/2013 Page 2 of 11
Displaying Text
Now that the LCD is set up, it’s time to start sending text to the display. To display a character of text on
the Serial LCD, simply send the ASCII code of that character to the Serial LCD over the serial port at the
correct baud rate.
When a character is received, the Serial LCD displays that character at the current cursor position and
then moves the cursor one position to the right. When you first turn on the LCD, the cursor is in the
leftmost position on the top line, as you might expect. The short bar on the bottom of the character
shows where the cursor is positioned currently.
Once you’ve sent a full line characters to the LCD, you will notice that the cursor automatically wraps
around to the leftmost position of the second line, just like the text in a book. The text will wrap like this
at the end of every line, with the end of the bottom line wrapping back around to the top line of the LCD.
The text will never “run off” the display; you’ll always see all of the characters you send.
Example code is provided below. You may download the example code files from the 27976, 27977, or
27979 product pages at www.parallax.com; just enter any of these product numbers in the “search” field
on the home page
BASIC Stamp
®
2 Example Code
You may download the example code from the 27976, 27977, or 27979 product pages at
www.parallax.com; just enter any of these product numbers in the “search” field on the home page. Try
the following code on your BASIC Stamp 2 to send a text string to the LCD display. First, set the baud
rate on your Serial LCD to 19,200. Then, load the code below into your BASIC Stamp 2 and run it.
You will see the text string show up and wrap to the second line of the display.
In all of your Serial LCD code, you should pause for 100 ms at start-up to give time for the Serial LCD to
initialize. You should also set the serial port pin on the BASIC Stamp to HIGH before the 100 ms start-up
delay, as this is the normal state of a serial port when it isn’t sending any data.
' {$STAMP BS2}
' {$PBASIC 2.5}
TxPin
Baud19200
HIGH TxPin
PAUSE 100
CON
CON
0
32
' Set pin high to be a serial port
' Pause for Serial LCD to initialize
SEROUT TxPin, Baud19200, ["Hello, this text will wrap."]
Propeller P8X32A Example Code
Try the following code on your Propeller to send a text string to the LCD display. First, set the baud rate
on your Serial LCD to 19,200. Then, load the code below into your Propeller and load RAM or EEPROM.
You will see the text string show up and wrap to the second line of the display.
In all of your Serial LCD code, you should wait for 100 ms after starting the FullDuplexSerial.spin object,
to give the object and the Serial LCD time to initialize. The FullDuplexSerial.spin object is included with
the Propeller Tool.
Copyright © Parallax Inc.
Parallax Serial LCDs (#27976, 27977, 27979)
v3.1 3/11/2013 Page 3 of 11
{{
Serial_LCD_Demo.spin
For Parallax Serial LCDs 27976, 27977, 27979
}}
CON
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
TX_PIN = 0
BAUD = 19_200
OBJ
LCD : "FullDuplexSerial.spin"
PUB Main
LCD.start(TX_PIN, TX_PIN, %1000, 19_200)
waitcnt(clkfreq / 100 + cnt)
' Pause for FullDuplexSerial.spin to initialize
LCD.str(string("Hello, this text will wrap."))
Moving the Cursor
When you send a character to the Serial LCD, it always displays at the current cursor position. There are
a few different ways to move the cursor on the Serial LCD display. After each character you send, the
cursor automatically moves over one position. Along with this, there is a standard set of cursor move
commands including Backspace, Carriage Return, and Line Feed.
The Backspace/Left command (Dec 8) moves the cursor one place to the left and the Right command
(Dec 9) moves the cursor one place to the right. These can be useful for moving the cursor around to
overwrite existing text. These commands wrap to the next line of the display, if necessary. The Line Feed
command (Dec 10) moves the cursor to the next line of the display without changing the horizontal
position of the cursor. The Carriage Return command (Dec 13) also moves the cursor to the next line, but
it moves the cursor to the leftmost position on that line as well. The Form Feed command (Dec 12) clears
the entire display and moves the cursor to the leftmost position on line 0, just like when you first turn on
the display. You will need to pause for 5mS in your code after sending the Form Feed command, to give
the Serial LCD time to clear the display. Except for Form Feed, none of these move commands affects the
characters on the display.
There are also direct move commands that you can use to move the cursor to any position on the display
with a single command. The commands in the range Dec 128 to 143 and Dec 148 to 163 move the cursor
to the 16 different positions on each of the two lines of the model 27976 and 27977 LCDs. The
commands in the range Dec 128 to 207 move the cursor to the 20 different positions on each of the four
lines of the model 27979 LCD.
Controlling the Display
You also have control over the various display modes of the Serial LCD. The display-off command (Dec
21) turns off the display so that all of the characters disappear. The characters aren’t erased from the
display, though, and you can even keep writing new characters to the display when it is turned off. A
trick to make a lot of text show up all at once, even at a slow baud rate, is to turn off the display and
then send all of your text. Then, when you turn the display on again, all of the text appears instantly.
Copyright © Parallax Inc.
Parallax Serial LCDs (#27976, 27977, 27979)
v3.1 3/11/2013 Page 4 of 11
The display-on commands (Dec 22 to 25) turn the display back on and also control whether you want to
display the cursor and/or make the cursor character blink. The cursor is the short bar that shows up
below the character at the current cursor position. The blink option makes that character blink on and off
repeatedly. You can turn the cursor and blink options on or off, in any combination, as listed in the
command set table. You can change the cursor and blink mode even if the display is already on; you
don’t need to turn it off and then back on again.
With models 27977 and 27979, you can also control the backlight of the display. The backlight lights up
the display so that it is easier to see in the dark. There are commands to turn the backlight on (Dec 17)
and off (Dec 18).
Custom Characters
The Serial LCD has the capability to store up to eight user-defined custom characters. The custom
characters are stored in RAM and so they need to be redefined if you turn off the power. You can display
the custom characters by sending the commands Dec 0 to 7, as shown in the command set table. The
custom character will display at the current cursor position.
The custom characters are five pixels wide by eight pixels high. Each of the characters is stored as a
series of eight data bytes where the low five bits of each byte represent a row of pixels in the character.
The high three bits of each byte are ignored. A bit value of one turns that pixel on (i.e. makes it black).
The bottom row of pixels is often left blank (all zeros) to make it easier to see the cursor.
To define a custom character, you will send a total of 9 bytes to the Serial LCD. The first byte needs to
be a valid define-custom-character command (Dec 248 to 255) and must be followed by eight data bytes
that define the pixels of the character. The Serial LCD will always use the next eight bytes it receives to
set the pixels of the character. The data bytes define the character starting at the topmost row of pixels,
as shown in the example code.
BASIC Stamp 2 Custom Character Example
Define a custom character using the code example below. First, set the baud rate on your Serial LCD to
19,200. Then, load the code below into your BASIC Stamp 2 and run it. You will see a diamond character
appear on the screen.
' {$STAMP BS2}
' {$PBASIC 2.5}
TxPin
Baud19200
HIGH TxPin
PAUSE 100
SEROUT TxPin, Baud19200, [250]
SEROUT
SEROUT
SEROUT
SEROUT
SEROUT
SEROUT
SEROUT
SEROUT
SEROUT
TxPin,
TxPin,
TxPin,
TxPin,
TxPin,
TxPin,
TxPin,
TxPin,
TxPin,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
Baud19200,
[%00000]
[%00100]
[%01110]
[%11111]
[%01110]
[%00100]
[%00000]
[%00000]
[2]
CON
CON
0
32
' Set pin high to be a serial port
' Pause for Serial LCD to initialize
'
'
'
'
'
'
'
'
'
'
'
Define custom character 2
Now send the eight data bytes
%00000 =
%00100 = *
%01110 = * * *
%11111 = * * * * *
%01110 = * * *
%00100 = *
%00000 =
%00000 =
Display the new custom character 2
Copyright © Parallax Inc.
Parallax Serial LCDs (#27976, 27977, 27979)
v3.1 3/11/2013 Page 5 of 11
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