piclist 2001\11\07\085432a >
Thread: LCD panel init problems
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face BY : Wollenberg, Frank email (remove spam text)



> This is the problem that I had some time ago. I discussed it
> at length with
> a rep from Noritake in Frankfurt (RemoveMEyyoshidaSTOPspamspamTakeThisOuTnoritake.de). It
> turned out that
> the requirement to have at least 3 reset sequences (hex 30) at
> initialisation is to avoid this particular problem. There are
> still things I
> don't understand, for instance, the number of reset sequences
> could be any
> odd number, but not even... Don't ask me why!

Jan,
Thanks for your reply.
I have not used a LCD in 4bit mode anytime. The problem i've described, was
theoretically (is it?).
I have read the data sheet and it seems for me, that there is no chance to
re-initiate the LCD.
The command "function set" (0x30) is a regular command, which can be send to
the LCD at anytime in two 4bit chunks, 0x3 followed by 0x0.
How can the LCD differentiate between this regular command and the command
as part of an initialisation sequence ?
Furthermore the above initialisation sequence (3 times 0x30) are described
in the data sheet in a context of inproper powerup. In this situation
nothing can be supposed, every flip-flop can be set to any state. A good and
reliable initialisation sequence must the be used. Again my question, how
can the LCD differentiate ... ?

Let me explain this example:
                 uP                                                   LCD
   send MSB of 0x8x (set DDRAM address)         LCD receives 0x8 (MSB of
set DDRAM address)
   uP resets because of whatever                LCD is still working
   uP sends 0x3 (1st part of init sequence)     LCD receives 0x3 as LSB of
DDRAM address
   uP sends 0x3 (2nd part of init sequence)     LCD receives 0x3 as MSB of
fucntion set (8bit)
   uP sends 0x3 (3rd part of init sequence)     LCD receives 0x3 as LSB of
function set
--> uP sends 0x2 (set 4bit i/f)                  LCD receives 0x2 as MSB of
function set (4bit)
   uP sends MSB of 0x2x                         LCD receives 0x2 as LSB
   uP sends LSB of 0x2x (N and F)               LCD receives
0x0/0x04/0x08/0x0c as ????
   and so on

The initialisation sequence has not set the LCD into 4bit mode after the uP
was resetting, the controlling uP and the LCD are still out of sync. Have i
missed something ?
It seems for me that all should be ok if the marked line should not be
executed.

But that's all theory. I've never tested this. What the rep from Noritake
has said is the same as the datasheet explains, but i can't verify this from
my experience. Why any odd number of 0x3 ? It makes no sense for me.

Because i must build the hardware first and then program (and debug) them
(and there is no time for experiments), i have gone the best way and decided
for 8bit mode interface.

Frank

GSP Sprachtechnologie GmbH
Frank Wollenberg
HW-Entwicklung
Tel.:   +49 (0)30 769929-78
Fax:    +49 (0)30 769929-12
eMail:  spamf.wollenbergKILLspamspamspam_OUTgsp-berlin.de


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