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[Lcdproc] hd44780 weird display/driver problem


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  • From: joris AT robijn.net (Joris Robijn)
  • Subject: [Lcdproc] hd44780 weird display/driver problem
  • Date: Sun Oct 6 20:32:02 2002

On 3 Oct 2002 at 9:42, Joris Robijn wrote:

> > So.. here are the docs I'm reading.
> > http://mywebpages.comcast.net/biglittlekid/systems/LCD_DMC_manual.pdf
> > Secion 1.7.4 (page 15) says there are exactly 80 bytes. This works with
> > my theory about the wrapping. Section 1.7.6.3 (page 17) says line two
> > starts at 0x40, but I think it's just wrong given the symptoms. Now the
> > important part is page 32, where it describes the initialization steps.
> > Note the extra stuff that lcdproc doesn't do. I have all this (but no
> > uPause after the third FUNCSET|8bit).
>
> You're completely right. It HAS 80 bytes and the source has a
> bug there. I'll fix that.
>
> I still gt surprised by how some bugs can remain in the source
> for these amounts of time. I need to connect my 40x4 too...

You almost got me. It seems like a bug from whatever angle you look. But
it isn't !

Now, what's the matter here. An HD44780 HAS 80 bytes only. It can work
with two 40 char long lines. However, the data of the second 40
characters starts at address 64 (0x40), not 40 ! So there is some kinda
gap of 24 bytes. That means that 0x40 in the code is correct.

BTW I did not need to connect my 40x4 to know this. A 20x4 also uses this
constant.

Joris






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