20x2 LCD displaying on only the first half

Varpulis · Joined: 26 Apr 2014 Posts: 4

I've got an urgent problem and I'm asking for your help.

My graduation project needs to be done in a couple of weeks but I've hit a wall. The LCD is displaying on only half the screen area and my mentor doesn't know whats causing it. I've searched for this problem but everywhere the problem is with 16x2 displays that need to be configured as something other than 16x2. There is never any mention for 20x2.

The LCD is DEM 20231 SYH-PY/V 427, connected for 4-bit transfer according to this schematic:

LCD goes through the initialization and displays 20 black squares in the first line for a second of 2 after power is turned on. After that it should display Brzina: (speed) in the first line and m/s in the lower line to the right but there are just some smudges... my guess is that in the picture the LCD tried to display a two number result. Something like 22.22 m/s. The squares lit up in the correct places but still something is wrong.

The code was written in Bascom-8051 version 2.0.14.0. I've translated it to English so its easier to understand. Its meant for a ballistic chronograph:

techknight · Joined: 21 Apr 2008 Posts: 230

That LCD is definitely faulty. You will need to replace it. One of the scan driver ICs failed.

albertsm · Joined: 09 Apr 2004 Posts: 5071 Location: Holland

you can best run a simple test :

$crystal = 24000000
$regfile = "89s8253.DAT"

Enable Timer0
Config Timer0 = Timer , Gate = External , Mode = 1
On Timer0 Pot
Enable Interrupts

Config Lcd = 20 * 2
Config Lcdbus = 4
Config Lcdpin = Pin , Db7 = P1.4 , Db6 = P1.5 , Db5 = P1.6 , Db4 = P1.7 , E = P2.1 , Rs = P2.0
CLS
dim x as byte
for x=1 to 80
lcd chr(x)
waitms 250
next
end

then see if the characters are visible on the screen.
otherwise post a link to the pdf of the lcd

Varpulis · Joined: 26 Apr 2014 Posts: 4

Thanks for the replies.

Any ideas what could have caused one of the driver ICs to fail?

I won't have access to the programmer next week but I'll run the test as soon as I can. Heres the LCD datasheet

albertsm · Joined: 09 Apr 2004 Posts: 5071 Location: Holland

i checked the PDF and the mentioned address is the same as bascom uses.
so my advise : try me code first. you must make sure that you do not call the CLS : lcd in a loop too quick.
if you have a cls too quick after the LCD it will fade away. so a first test should be where you show data and then quit to program.