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Author Topic: Details on LCD interfacing  (Read 4840 times)

tac_evaworcim

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Details on LCD interfacing
« on: September 24, 2012, 05:47:38 PM »
Can anyone provide the details on how to connect a TFT lcd to the board?
I suppose LCD_CON can be used to provide parallel RGB signal, but some moments are not obvious.  ???

1) Are d0-d7 represent Red, d8-d15 Green, d16-d23 Blue? Or they are swapped?
2) What is "CPU mode" of LCD interface? Is it for LCD panels with a controller onboard? (like SSD1289, SSD1963 etc)
If so, should I use LCD panel's controller or should I better connect the LCD to A13 directly?

I have a HannStar hsd050idw1-a20 5" 800x480 TFT panel with 4-wire resistive touchscreen and separate SSD1963-based controller board. Can it be connected to the Olinuxino A13, and what is the best way to do that?

LubOlimex

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Re: Details on LCD interfacing
« Reply #1 on: September 25, 2012, 11:21:02 AM »
Hello there,

1) Please check this excerpt of the schematics: http://i.imgur.com/yLhYj.jpg The labels and names you care about are the magenta ones. They are pretty self-explanatory (R for red, G for green, etc.). Note that some of the other signals like display control might differ from the ones of your display (as a name) and you might need to play a bit.

2) No controller on the LCD required. Connect directly.

The resolution of the display you have is exactly the same as the one we used here (800x480) and the touchscreen interface is also the same.

Lub/OLIMEX
Technical support and documentation manager at Olimex

tac_evaworcim

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Re: Details on LCD interfacing
« Reply #2 on: October 06, 2012, 12:07:20 PM »
Thank you for a reply.

I managed to connect the lcd, but have some trouble switching it on with android.
I think it's something about VGA_DIS pin. How to use it properly? I tried to pull it up to 3.3V with 47K resistor, connect to 3.3V directly, etc.. Whatever I try, VGA out continues to work, but lcd does not..
However, a touchscreen is working great, though blind-calibrated.

Should I initialize the display somehow, or it should work as soon as connected?

MrPec

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Re: Details on LCD interfacing
« Reply #3 on: October 06, 2012, 01:35:12 PM »
I also use a parallel rgb display. I haven't had to initialize the display somehow, and I'm almost sure that the vga and lcd connector use the same signals, and I think that you can't switch between them.

I would first check if the backlight is working.

tac_evaworcim

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Re: Details on LCD interfacing
« Reply #4 on: October 06, 2012, 07:51:43 PM »
the backlight doesn't turn on no matter what I do :(
I assume backlight pins on LCD are Vled-/Vled+
First I connected it directly to the ground/5v, then tried 3.3 v, then PIN6/PWM0 (BKL) pin of the LCD interface.
It does not turn on :(
I even tried to connect a simple led to the PWM0 pin, and it does not turn on either.
Though the display is working great when I connect it to another board (SSD1963 controller).

Some doubts: What is the purpose of PWRE, L/R, U/D pins ? I didn't connected them.
Another not-matched pin, named "DISP" is on LCD, datasheet says it's "Display On/Off" input pin. No other info is provided, so I assumed to pull it up to 3.3v line.

But still the display is dark.

What I may doing wrong?

PS: Just curious, how the board knows the resolution and timings of the connected display if I don't initialize it anywhere?
« Last Edit: October 06, 2012, 08:06:33 PM by tac_evaworcim »

MrPec

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Re: Details on LCD interfacing
« Reply #5 on: October 06, 2012, 08:48:24 PM »
It looks like your display has no step up regulator for the backlight. According to the datasheet you need 23V, because you have to drive 14 LEDs, and about 40mAh. Just use a power supply for now, I think a voltage from 12V could work....

PWRE is I guess power enable, it'sused to shut down the display. L/R and U/D is the scanning direction, it's just to mirror the display (up/down, and, guess what, left/right :)).

First try to get your backlight to work!

tac_evaworcim

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Re: Details on LCD interfacing
« Reply #6 on: October 06, 2012, 09:39:49 PM »
Ok, I'm trying to do it, will report shortly.
but why even a simple led does not lit on olinuxino's PWM0 pin?

tac_evaworcim

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Re: Details on LCD interfacing
« Reply #7 on: October 07, 2012, 12:28:24 AM »
Thank you for pointing out the regulator issue. This is the first display I'm trying to connect directly, I only used a controller-attached displays before (e.g. SSD1963, SSD1289, etc..).
unfortunately, 12V/1A power supply trick failed..
It does not glow, even lightly. :(


MrPec

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Re: Details on LCD interfacing
« Reply #8 on: October 07, 2012, 01:10:17 AM »
According to the datasheet you need 23V, you should try that... You must see it then, because the backlight contains only 2 parallel strings of several leds in series. You should also limit the current to about 40mAh.

tac_evaworcim

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Re: Details on LCD interfacing
« Reply #9 on: October 07, 2012, 02:25:22 AM »
Unfortunately, I have no suitable power supply at hand..

I thought if the leds have no enough power, they should lit a bit at least. My is completely switched-off.
Another strange thing is that PWM0 doesn't drive even a simple single low-current led connected to it.
I thought it should.
These fundamental oddities makes me feel weird.


MrPec

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Re: Details on LCD interfacing
« Reply #10 on: October 08, 2012, 09:48:17 AM »
Maybe you have toasted that pwm pin. According to that datasheet, there's no resistor to protect the i/o pin.