"Chris Fonville" schreef in bericht
...
Alexander wrote:
"Chris Fonville" schreef in bericht
...

This is my first LCD and I am not having much luck. I have checked over
my wiring many many times and cannot seem to find the problem. It is a
4x20 hd4780 LCD. When I turn it on the backlight comes on and I receive
the test signal, but some lines are missing. The top 4 squares, or I
guess pixels, are on but then the next 2 down are not. The bottom 2 are
also on. Here is an example of one character:
*****
*****
*****


*****
*****
This is repeated for each character on the 1st and 3rd line of the LCD.
Is this a bad LCD or do I have my wiring wrong? Also, I can use LCD
Smartie and the LCD will respond but I can only make out some characters,
but most of the screen is gibberish. How can I go about fixing this
problem? Any help will be appreciated. Thanks,
Chris


Chris,

normally you send the ascii code of a character to the LCD (controller),
if this character is displayed on one or more line(s) correctly, you have
initialized and send a succesfully this character. If you only use the
controller's own characters this character is always displayed correctly,
if this character is missing a line (or more) then most likely the
display is broken.
So in your case send one character to all positions, you should see 4*20
of the same character (or one different because of cursor), if not try
another display.

Good luck,

Alex

The example I posted above was just from the test screen. This happens
when the LCD is not connected to the parallel port, but is just receiving
power. If I understand correctly, every other line of the 4 should be on.
This happens with mine, however each character is 8 blocks or pixels high
and only the top 4 are on, 2 are not, then the bottom 2 are on. This
happens all the way across the screen. This is hard to explain in words,
I have uploaded some pictures:
Test screen with and without parallel connection
http://www.chriscomputers.com/lcdtest.jpg
Using LCD Smartie to put "ABC" on all 4 lines
http://www.chriscomptuers.com/lcdabc.jpg

You can sort of make out ABC in lines 2 and 4. Because I can actually
send it commands and it display them somewhat, and because the LCD test
screen is not fully working with just power, I think it is either my power
wiring is wrong or the LCD is defective. Thank you for your help,
Chris

It looks like a defective LCD-Module, but I have never seen a similar
problem, try disconnecting the enable line or shutting down the device that
gives command to the LCD is the ABC stays the same way it's the LCD-Module.
If it changes and gives either blocks or good ABC then you are changing what
the module should display rather fast.

Good luck,

Alex