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PICList Thread
'16x2 LCD control problem.'
1999\01\04@130313 by Skybyte

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-- 3nd post --

       Hi all,

I have a 16x2 LC Display and I want to send some text to it with a
PIC16c84.
I programmed the PIC with the hex file and... the LCD does nothing,
really
nothing.
The LCD data bus is connected to the 8 outputs of a HEF4094 (i'm using
8-bit mode).
Before I start checking the program for bugs, I would like to know
whether
i connected the LCD properly.
My Quetsion: LCD has 14 pins which I am using. pin 1=GND, pin 2=+5V,
pin3=Contrast. (and other pins...)
But what do I do with the 2 blobs of solder on the right hand  side of
the
LCD? It says Anode and Cathode. Is this the connection for the
backlight,
XOR is it the main +5V power connection which HAS to be connected?
Currently it's left open.

Thanx VERY much, because I can't stand those things when they don't
work.
Skybyte, from the Netherlands.
       spam_OUTSkybyteTakeThisOuTspamdds.nl

'Why worry about next year? The romans, 1000 years ago, didn't encounter
any millenium-problems either.'

1999\01\04@141906 by Bob Blick

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You didn't say what you had done with pin number 3. If it is a standard
display, ground it. If it is an extended temperature display, you need an
adjustable negative voltage supply.

Even without any code, you should see the first line "energize" slightly
if you have the correct contrast voltage.

You probably didn't get much response from your other two posts because
you were not specific about how you connected your display, and there are
also those of use who would say "first time user of an LCD should not use
a shift register, learn to use the LCD as the first step" but were too
polite and waited for someone like me to say it :-)

-Bob

1999\01\04@173630 by paulb

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Skybyte wrote:

> -- 3nd post --

 *WHY* are you posting this a third time?  I hope it's not because you
get a "message undeliverable" reply.  If so, you have much to learn
about e-mail and particularly, common sense.

 Specifically, if it says "undeliverable"; it *means* it, and no amount
of bloody-minded resending is going to stop that message, but an
audience of 1800 watching your repeated efforts are *not* going to be
amused, and will likely tell you so.

> The Contrast pin gives a readout of 5.0V, the same as Vdd. However,
> There is a 10k pot connected between +5V and the Vee contrast pin of
> the LCD. Pot is in the middle, at about 5k (i checked it).

> I really don't understand.

 Your external potentiometer should be connected *between* +5V and
ground with the *wiper* going to pin 3.  Pin 3 is pulled up to 5V by an
internal divider chain (five resistors) which sets scanning voltages, so
if you don't provide bias, there is *no* drive to the display at all.

 Most displays work with a contrast voltage of zero, so grounding the
Contrast pin is a quick approximation.  Presuming you fit the 10K pot,
you will probably find the best working point near here.  If it only
*just* works when the pot is wound to the ground end, this indicates you
need to return the pot to a negative voltage (and that's another topic).

 The chip will initialise and you will see the first line "dark up"
with the correct contrast voltage and *no* initialisation sequence, and
that's what you are looking for.  Despite Bob, I think that if you get
this far, the shift register if fair cop.  What I *wouldn't* recommend
is learning to use 4-bit mode before you've mastered 8-bit.
--
 Cheers,
       Paul B.

1999\01\04@201829 by James Cameron

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Paul B. Webster VK2BZC wrote:
> [...] an audience of 1800 watching your repeated efforts are *not*
> going to be amused, and will likely tell you so.

Actually, I've been thinking of just making a little note against their
name saying "net.credibility < 0", and send a little training note back.

Perhaps I need to start a collection of FAQ-like training notes ready
for posting.

--
James Cameron                                      (.....cameronKILLspamspam@spam@stl.dec.com)
"Specialisation is for insects." -- Robert Heinlein.

1999\01\05@103746 by ose Antonio Gracia Negre

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I have had problems with the LCD and the cause was the boot sequence. Send
one for 8 bits, but I have used it of 4 bits

Initialization sequence for HD44780

power ON
   Ï
WAIT more than 15 ms. after Vdd rises to 4.5V
   Ï
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     1     1     *      *    *     *        (function set
(interface8 bits long))
   |
WAIT more than 4.1 ms.
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     1     1     *      *    *     *
   |
WAIT more than 100 micros.
   |
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     1     1     *      *    *     *
   |
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     1     1     N      F    *     *     function ser
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     0     0     1      0    0     0        display off
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     0     0     0      0    0     1         display ON
rs rw db7 db6 db5 db4 db3 db2 db1 db0
0  0    0     0     0     0     0      1   I/D    S        entry mode set

N=1      2 lines     N=0     1 line
F=1   5x10 dots    F=0  5x7 dots
I/D=1  increment        I/D=0  Decrement

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