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abhishek_sharma
06-24-2005, 12:23 PM
hi guys,

i am newbie who has just a couple of months of experience in electronics,etc...
i am trying to interface an lcd in 4 bit mode. for the purpose i bought a 16*2 lcd with backlight without asking the shopkeeper if it was a hd44780 compatible or not.

now when i power it using a lm7805, i.e. + 5 v i see blocks only on lower half of the display, the upper half is seen only when i power it using a 9 v supply(which i beleive is dangerous for the lcd)
the squares are too dark and the contrast adjust works differently for the upper and lower half of the display.
i interfaced it in 8 bit mode using a prewritten program but nothing happened.

i feel like crying and don't know what is wrong with the module. i know the software part is right since i got it from a tutorial.

plz help....

happy_99
06-24-2005, 11:39 PM
Hi,

Tell me which PIC u are using. Could you give me the circuit that u are using. I'll see if i can do something. By the way is there something written on the LCD.

Howz it possible to use 8bit lcd in 4bit mode?

Regds

happy_99

abhishek_sharma
06-25-2005, 06:51 PM
yes, happy99, jhd 162A is written on the LCD. by the way iam interfacing it to the parallel port of the computer :D

06-26-2005, 11:57 AM
Howz it possible to use 8bit lcd in 4bit mode?

I'm using a JHD 162A in 4-bit mode. I've hooked it to an AVR. I dont know the protocol coz i use library functions of CodeVisionAVR. everything works well. and requires just 7pins in all!



the squares are too dark and the contrast adjust works differently for the upper and lower half of the display.


Try shorting the contrast pin and ground.

ice
06-26-2005, 09:41 PM
abhishek
wire ur contrast pin(probably pin 3 ) to gnd and check it.



Howz it possible to use 8bit lcd in 4bit mode?

There are 2 ways to wire up the hitachi LCD...either in a 4 bit or an 8 bit mode..

in the 4 bit mode..
The uppernibble is transferred ,then the lower one
Normally used when you have less I/O pins on the board..

in the 8 bit mode..
The whole byte is slammed in..

RHESSque
07-07-2005, 12:56 AM
Check the following... It MIGHT be the reason...

Some LCD's require negative biasing to operate.

AFAIK you have to issue a command to make use of both lines...but then again it doesn't make sense why your bottom line is working and not your top line coz normally it's the reverse...anyway the command is sumtin like
Function Set(4bit/2line/5x7) : 00101000

my 2cents worth...

vikas
07-07-2005, 10:33 AM
I faced a similar problem once ( Its when you dont intialize the LCD properly )

http://www.roboticsindia.com/modules.php?name=News&file=article&sid=75

read the article ... You just have to intialize ur lcd into proper mode [ elso only half of it works ] .