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20x2 LCD displaying on only the first half

 
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Varpulis

Bascom Member



Joined: 26 Apr 2014
Posts: 4

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PostPosted: Sat Apr 26, 2014 7:47 pm    Post subject: 20x2 LCD displaying on only the first half Reply with quote

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:

Code:
$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
Cursor Off

Dim A As Byte , Ctr As Word , Nbr As Long , Sum As Long , Time As Single , Spd As Single , Targ As String * 6

Check:
A = 0
Counter0 = 0
Cls
Lcd " Speed:"
Locate 2 , 10
Lcd Targ ; " m/s"

Do
Debounce P1.0 , 0 , Cstart
Loop

Cstart:
Start Timer0
Do
If P1.1 = 0 Then
Goto Cstop
End If
Loop

Cstop:
Stop Timer0
Ctr = Counter0
Goto Calc

Pot:
Incr A
Return

Calc:
Do
Nbr = 65535 * A
Sum = Nbr + Ctr
Time = Sum / 2000000
Spd = 0.3 / Time
Targ = Fusing(spd , #.##)
Goto Check:
Loop


Is the LCD faulty? Did I make an error in the code or wiring? This problem makes no sense to me since the LCD is brand new and both the schematic and code were tested on another board with a 16x2 LCD and proven correct.

(BASCOM-AVR version : 2.0.14.0 , Latest : 2.0.7.7 )
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techknight

Bascom Member



Joined: 21 Apr 2008
Posts: 230

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PostPosted: Sat Apr 26, 2014 8:02 pm    Post subject: Reply with quote

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

Administrator



Joined: 09 Apr 2004
Posts: 5071
Location: Holland

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PostPosted: Sat Apr 26, 2014 9:19 pm    Post subject: Reply with quote

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

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Varpulis

Bascom Member



Joined: 26 Apr 2014
Posts: 4

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PostPosted: Sun Apr 27, 2014 1:00 pm    Post subject: Reply with quote

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
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albertsm

Administrator



Joined: 09 Apr 2004
Posts: 5071
Location: Holland

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PostPosted: Mon Apr 28, 2014 10:18 am    Post subject: Reply with quote

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.

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