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README for HD44780 driver git-svn-id: https://ssl.bulix.org/svn/lcd4linux/trunk@49 3ae390bd-cb1e-0410-b409-cd5a39f66f1f
97 lines
4.6 KiB
Plaintext
97 lines
4.6 KiB
Plaintext
#
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# $Id: README.HD44780,v 1.2 2000/04/19 04:44:20 reinelt Exp $
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#
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This is the README file for the HD44780 display driver for lcd4linux
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This driver supports all display modules based on the Hitachi HD44780 chip.
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These displays are made by different manufactures, and come in various sizes.
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The following types are known to work:
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DataVision DV16244: 2 lines by 16 characters
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Nan Ya NLC 08x2x06: 2 lines by 8 characters
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The displays are connected to the parallel board (see Wiring below), and are quite timing-critical.
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There's no way to delay a usermode program under Linux for e.g. 40 usec, so we have to do
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busy-waiting. This is done in a delay loop, which has to be calibrated (see Configuration below).
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The driver supports vertical, horizontal and split bars (two independent bars in one line),
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all bar types can be used simultanously. As the displays only have 8 user-defined characters,
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the needed characters to display all the bars must be reduced to 8. This is done by replacing
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characters with similar ones. To reduce flicker, a character which is displayed at the moment,
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will not be redefined, even if it's not used in this run. Only if the character compaction
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fails, this characters will be redefined, too.
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Configuration:
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The driver needs the following entries in lcd4linux.conf:
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Display: HD44780
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Port: the hexadecimal address of the parallel port (e.g. 0x378)
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Size: [columns]x[rows] e.g. "16x2"
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Delay: calibration of the delay loop, loops per microsecond
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It is very important to use a correct delay value, otherwise you will get only junk on the
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display. lcd4linux has a switch '-d' where it helps you to find the correct value. Run
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'lcd4linux -d' several times on a otherwise idle machine, and use the maximum value. If you
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encounter display problems, increase this value. But don't take it too big, lcd4linux will get
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slow, and you're burning CPU cycles.
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The delay value is defined by your CPU model and clock frequency (it looks like it's your
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'BogoMips' value divided by 2, because we use a similar delay loop than the kernel does).
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Here are some examples:
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Pentium MMX, 133 MHz, 106 BogoMips: 54
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Pentium MMX, 166 MHz, 333 BogoMips: 166
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Celeron, 333 MHz, 333 BogoMips: 166
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Pentium III, 600 MHz, 600 BogoMips: 300
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Wiring:
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There are two basic wiring modes for HD44780-Displays: a 4 bit mode (used by lcdproc) and a
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8 bit mode (used by most other packages). At the moment we only support the 8 bit mode, but
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I'm working on the 4 bit mode, too.
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The main difference is that the 8 bit mode transfers one byte at a time, but the HD44780 needs
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some control signals, so some of the parallel port control lines are used for this. The 4 bit
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mode uses only 4 bits for data (so a byte has to be transferred in two cycles), but you can use
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the other 4 bits for the control signals.
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Normally a HD44780-based display have 14 or 16 pins, where pins 15 and 16 are used for backlight.
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Power (+5V) must be supplied via pins 1 and 2, be careful not to change polarity, you will
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destroy your display! Pin 3 is used to control the contrast, you can either hardwire it to GND
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(pin 1) or place a potentiometer (10k-20k) between pins 1 and 2, and connect pin 3 to the slider.
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Note that the data bits are called DB0..DB7 on the display, but DB1..DB8 on the parallel port!
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Here comes the wiring diagram for the 8 bit mode:
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--- Display --- --- DB25 --- --- comment ---
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Name Pin Pin Name
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GND 1 18 GND GND of power supply, too!
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+5V 2 - power supply only
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LCD drive 3 - see above
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RS 4 14 Auto Feed register select, 0=data, 1=command
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R/W 5 18 GND hardwired to 0, write data only
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Enable 6 1 Strobe toggled when data is valid
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DB0 7 2 DB1 data bit 0
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DB1 8 3 DB2 data bit 1
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DB2 9 4 DB3 data bit 2
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DB3 10 5 DB4 data bit 3
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DB4 11 6 DB5 data bit 4
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DB5 12 7 DB6 data bit 5
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DB6 13 8 DB7 data bit 6
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DB7 14 9 DB8 data bit 7
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+5V 15 - power for backlight
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GND 16 - power for backlight
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10-13 not connected
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15-17 not connected
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19-25 not connected
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Wiring diagram for 4 bit mode: soon to come!
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