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[Lcdproc] HD44780 40x4 with Backlight and winamp wiring

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  • From: ethan.dicks at (Ethan Dicks)
  • Subject: [Lcdproc] HD44780 40x4 with Backlight and winamp wiring
  • Date: Thu, 22 Jan 2009 12:48:25 -0500

On Thu, Jan 22, 2009 at 12:23 PM, Sascha <sascha.zielinski at> wrote:
> Hi,
> I bought a 40x4 LCD with LED Backlight...

Nice. I have a couple of those.

> I connected the Display as shown below...

> Printer LCD
> 1 9 EN1
> 17 15 EN2

OK.... 8-bit wiring w/dual enable. Standard AFAIK.

> Additionally there are the pins 17+18 on the LCD, which are not in the
> Datasheet. These pins are for the LED Backlight I think.

Probably. Mine have extra pins for backlight - one is away from the
interface connector, one is extra pins on the interface connector.

> The Documentation describes to connect the Backlight pin through the BC327
> Transistor to Pin 17 of the Printer Port.

Yes. That is the "standard" way to hook up a backlight.

> Should I then connect the EN2 to GND?

If you do that, then you will only be able to use half of your display.

The "problem" is that there aren't enough pins for an 8-bit interface,
plus 2xHD44780 (EN1 + EN2), *plus* backlight. AFAIK, all 40x4
displays are implemented as two HD44780s with all pins tied together
except enables. This is because there isn't enough onboard RAM (or
column/row drivers, too?) to handle 160 on-screen chars with a regular
HD44780, and I don't think anyone extended the chip that way - it's
easy enough to add a second controller chip to the back of the LCD,
and there's plenty of room.

> I use Debian Unstable/Experimental. The Version 0.5.2 compiles fine and runs
> now for about a day without a problem. I tried also the the version from cvs
> server (checked out on 01.22.09 at 5.00 pm CET). If I start LCDd with my
> LCDd.conf from stable version, the Lines 3+4 stays blank.

Interesting... if your displays is two 40x2s together, it sounds like
you aren't getting the second enable lit up when it needs to be.

The stable 0.5.2 is quite old now. It's entirely possible that
features have been added that are affecting your experience. I've
been using nightly tarballs for years now, since I do driver
development, and have had no problems with either of my 40x4s on a
usb4lcd interface (which uses the HD44780 driver, the same as what you
should be using). I have not tried using my 40x4s with the stable
version of the code, nor do I have a handy cable to trying them out on
the parallel port, sorry.

If you read C, you could try browsing the hd44780*.c code and see if
there were any changes made since 0.5.2-stable that might come into
play. I'm wondering how long tying two displays into one virtual
screen has been around, or if perhaps the default line for EN2 may
have changed in the past couple of years.

I don't know that lots of the people on this list have 40x4 displays,
but perhaps someone with a parallel-attached LCD can comment. I
mostly work from laptops now, and few laptops provide parallel ports
anymore. Even serial ports are getting scarce. :-( I'm doing more
and more work with USB-attached displays even though I miss the
directness of driving ones own I/O ports without an intervening
software layer to debug.


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