"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

If you connect the first three pins only Vss, Vdd and Vo, the first line
(and perhaps the third line) should be all blocks with the character width
and height.