LCD module driver README
Hardware
--------
This is for a 20 x 4 character LCD display based on the Hitachi HD44780
controller. Additional displays with other geometries should be suppported by
editing "hardware.h" and setting LCD_COLS and LCD_LINES correctly. I just
have the 20x4 display so it is only tested for this. The display can easily
be wired to a standard PC parallel port.
Just connect the eight data bits to the eight inputs of the display plus
STROBE (pin 1 on 25 pin Sub-D) to EN (enable) and FEED (pin 14 on 25 pin
Sub-D) to RS (command-/datamode). You will also have to connect GND
to the read/write selector input. The driver does not need to read from the
display so we can hard-wire the write mode. Don't forget to add at least one
GND line. The 5V power supply for the display can easily be obtained from a
game-port adapter.
25 pin LCD
SUB D Panel Pin
---------------------------
GND 1 --+--- \ Connect to
+5V 2 --|--- / Gameport
R/W 5 --+
1 EN 6 |
2 DB1 7 |
3 DB2 8 |
4 DB3 9 |
5 DB4 10 |
6 DB5 11 |
7 DB6 12 |
8 DB7 13 |
9 DB8 14 |
14 RS 4 |
18-25 GND --+
Pin 3 on the LCD is the LCD driver control voltage input, i.e. contrast
regulation. My display shows very good contrast when I wire it directly to
GND. Other display may need a real driver current. You can use a
variable resistor (>= 100 Ohm) to do it like this
+5V ---+
/
\ <--+
/ |
\ |
GND ---+ +--- VL (Pin 3 - driver input)
The PC game port offers several +5V lines that can be used as power supply.
You can use
DB15 pins 1,8,9 or 15 for +5V
4,5 or 12 for GND
But please try to verify this for your hardware because some soundcards may
carry additional signals like a Midi port on those lines.
Installation / compilation
--------------------------
1. choose the correct definition for Kernel 2.0.* or Kernel 2.1.* (use
-DKERNEL21 for Kernel 2.2.* too).
2. edit the port address of the used parallel port in 'hardware.h' !
3. choose the correct number of lines and columns in 'hardware,h' !
Now just type 'make' to build the module.
Create a character device major 120 minor 0, you may choose to use the
included script 'mkdevice' for this.
'insmod' the module without any options.
Device is initialized (set initial mode, clear display, turn display on)
when module is inserted. You should see an underline cursor not blinking in
the upper left corner.
Now just write text to the device, done ;)
German "Umlaut" characters are mapped correctly. Additional mappings can be
done in "c_table.h".
Valid ESC commands:
ESC c - Clear display
ESC h - Home cursor
ESC R - Reset display
ESC # - Define user definable char number #
Defining a character:
Characters are organized in 8 bytes per row (!) with last three bits
ignored for displays with 5x7 fonts. My display can also use 5x8 fonts,
i.e. the characters may use the cursor line. A character is defined as
D7----D0
00011111
00010000
00010001
00011111
00010001
00010000
00010000
00000000
which is something like a big F.
To define this character as char number 0 you will have to write the sequence
27 0 31 16 17 31 17 16 16 0
to the LCD device (which is ESC-0-31-16-17-31-17-16-16-0).
You can do this from your shell using the echo command with the "-e" switch
like in
echo -n -e "\33\0\37\20\21\37\21\20\20\0" > /dev/lcd
A subsequent
echo -n -e "\0" > /dev/lcd
will print the new character. The "-n" just suppresses a trailing line-feed.
Terminal-like behaviour:
If during write cursor reaches the right most character the cursor is
positioned at the beginning of the next line.
Line-feed character (dec 10) causes the cursor to move to the beginning of
the next line.
Carriage-return (dec 13) causes the cursor to move to the beginning of the
current line.
Installation
------------
If you use something like kerneld, i.e. automatically load modules when
needed, you might want to copy the driver 'lcd.o' to your modules directory
and add the following line to your 'conf.modules'
alias char-major-120 lcd
After that update your module's dependencies by doing 'depmod -a' and the
module should load automatically when /dev/lcd is accessed.
Testing
-------
You should have received some test programs with this package. After the
display is installed and the module is inserted correctly you should be able
to run them and see the output.
Try "./nice". It should display date,time and processor load every ten
seconds.
You may also try "make test; ./bla". This program will at first display a
sequence of "12345..." in every line so you can count the number of
characters ;) After pressing a key the whole font is displayed filling the
whole screen with one character each and going through all characters >=32.
Usual blah-blah
---------------
This driver is incomplete and may crash your machine.
Also wrong wiring may cause severe damage to the display and to your
computer.
The driver is free software but
(c) Siegen (Germany) 1998,1999, by Nils Faerber
GNU Public License applies
Thanks go to:
Michael Engel - for getting me started with driver programming
Graham Stoney - for testing another display and a small fix