[Lcdproc] 4bit-HD44780 and keymatrix...

[Markus Dolze]

Hi,

-------- Original-Nachricht --------
> Datum: Wed, 23 Dec 2009 20:29:40 +0100
> Von: "Thorsten Godau" <dl9sec at gmx.net>
> An: lcdproc at lists.omnipotent.net
> Betreff: [Lcdproc] 4bit-HD44780 and keymatrix...

> Hi all,
> 
> as described in a thread above, i am using a EA DIP204-4 (HD44780->KS0073)
> connected the "4bit"-way to the parallel port.
> As i undestood the documentation, the other signals, that are not used
> for display control can be used for a keymatrix and defined and enabled
> as per an entry "keymatrix_X_Y" in the configuration file.

You can use all lines, except those used as Enable-signal and backlight switch. In case of the 4bit-wiring, you *can* use D0-D4 on the parallel port, even if the are connected to the display.

> 
> My keymatrix is the following:
> 
>   +5V ----------+---------+--------+---------+
>                 |         |        |         |
>                22k       22k      22k       22k
>                 |         |        |         |
>    Y7 -|<|--+---------+--------+---------+   |
>             |   |     |   |    |   |     |   |
>             o   |     o   |    o   |     o   |
>           S1 \  |   S2 \  |  S3 \  |   S4 \  |
>             o   |     o   |    o   |     o   |
>             |   |     |   |    |   |     |   |
>             +---+     +---+    +---+     +---+
>                 |         |        |         |
>                 |         |        |         |
>    Y8 -|<|--+------------------+---------+   |
>             |   |         |    |   |     |   |
>             o   |         |    o   |     o   |
>           S5 \  |         |  S6 \  |   S7 \  |
>             o   |         |    o   |     o   |
>             |   |         |    |   |     |   |
>             +---+         |    +---+     +---+
>                 |         |        |         |
>    X1 ----------+         |        |         |
>                           |        |         |
>    X2 --------------------+        |         |
>                                    |         |
>    X3 -----------------------------+         |
>                                              |
>    X4 ---------------------------------------+ 
> 
> After being not very successful getting my LCD to work with LCDd,
> i tested the function of the keys in debug mode.
> 
> Unfortunately S1/S5, S3/S6 and S4/S7 are delivering the same keycode
> (letter) if being pressed.
> So for me it seems, that the Y-lines are not really toggling from high
> to low and vice versa round robin to get the scanning-effect.
> They seem both to be statically low.
> 
> Can anyone confirm that behaviour?

No, I explicitly tried this with my 3x4 matrix keypad and it did work.

Note that when using the 'keymatrix_x_y' with the wiring above you have to use it like this:

keymatrix_2_8=S1
keymatrix_3_8=S2
...

The 'keymatrix' setting counts from '1' whereas the Y# and X# lines are counted from '0' in the documentation.

The keypad is not scanned in a round robin fashion, but like this:

1. Check with all Y = '1' to detect direct keys.
2. Check with all Y = '0' to detect if any key has been pressed.
3. Do a binary seach on Y to find the key actually pressed.
4. Do a final read (not strictly necessary in some cases, but it doesn't hurt).

I added some more comments recently to document what I read: http://lcdproc.cvs.sourceforge.net/viewvc/lcdproc/lcdproc/server/drivers/hd44780.c?r1=1.94&r2=1.95

Regards,
Markus