LCD LVDS Wiring - Controller to Panel

Cosmas · 11-22-2008, 03:45 PM

I was reading a post on LVDS/TTL cabling and I've been trying to wire up a 27" panel for some time now as a side project.

I don't quite understand how the differential data on my panel works and I was hoping someone could explain the theory behind it. I've got a pinout of the panel itself, which is very straightforward. And then I've got the pinout for a controller I bought from a German outfit who gave minimal data on it.

The panel is 1280x720 and claims 8-bit color. The spec says that the first pixel is even, but does that then mean that the next would be odd? Or are they all even? I've got it wired all even right now and I don't have a picture. I'd greatly appreciate any input on this.

Here's the full 27's spec if someone wants to take a gander. I've got 4 of these bad boys I really want to do something amazing with.

eeguru · 11-22-2008, 05:20 PM

Are you sure the controller is LVDS? It sure doesn't look like it. The odd/even designation on the controller spec may refer to it being a dual link transmitter. In dual link mode, 2 pixels are transmitted at once per clock over a second set of diff pairs. Yet the sheet says "pixel n" instead of 'channel n' or 'pair n' like it should. It also shows a separate line for DE which is usually a bit that gets mapped in the LVDS clocking (along with 18-bit RGB, H Sync, V Sync = the 21 clocking bits for 3x7 channel LVDS - with the 4th channel carrying the 2 LSBs for 24-bit RGB color).

Something looks a-miss. Do you have a full spec sheet for the transmitter?

Cosmas · 11-22-2008, 08:28 PM

Not a full sheet no, they didn't provide that. Just these few pin diagrams.
The only others I have apart from the one posted are:
Mainboard Display - which doesn't even look consistent with the actual board.
Connector 7 - Which isn't even on the board.
Main Power Connector - Pretty Normal.

Where I got it from - When I bought it the desc was in English. It claims to be universal, so I would imagine I could use EITHER the even or the odd. They provided all these files and a few more in this zip file from their website.

eeguru · 11-22-2008, 10:01 PM

May just be a miss-translation in the pin outs. Maybe they do mean channel instead of pixel and they provide DE separately as well as in the LVDS sequencing.

Try each set of diff pairs and see what happens imo.

Cosmas · 11-23-2008, 12:45 AM

Well see thats what I don't understand. Are you typically supposed to alternate even/odd or straight even or straight odd? All I know is the first pixel is even.. ok but then what? I'll try just swapping around like you say guru, I don't imagine I'll do any permanent damage with that low of voltage.

The only other thing that perplexes me is the power input lines. Do I wire the panel directly to the power supply or is that supposed to be power coming out of the controller going to the panel?

eeguru · 11-23-2008, 11:46 AM

No what I'm saying is 'maybe' there was a translation error. And where they say 'EVEN/ODD datal' in that pin-out they mean LVDS link number (where every other pixel really is transmitted on alternating links in dual link mode). And where they say 'Data of pixel n' they mean LVDS channel n (on that link).

I don't think you'll hurt anything as long as you wire the supply and ground correctly. You're display is a single link device. So wire up either the odd (likely the first link) or the even set of diff pairs to the diff pairs on the LCD and see if you get sync lock.

Cosmas · 11-23-2008, 12:35 PM

Ah, ok. I'll try that out and report back.

tom61 · 11-24-2008, 09:34 PM

Is this controller designed for LCD TVs? Most designed for computer LCDs don't handle widescreen LCDs.

Cosmas · 11-24-2008, 10:15 PM

As far as I know this is just for LCDs. I certainly don't know of any TVs that come with DVI on them. I'm beginning to think that the documents they provided me are incorrect, because I can't get any of these to respond.

I hooked up the even side again and its a white screen with some dabbles of other colors flashing by. Occasionally I'll get pixelated boxes of RGB jumbling resembling something like TV static except, RGB.

tom61 · 11-26-2008, 06:33 PM

Quote: Originally Posted by Cosmas

As far as I know this is just for LCDs. I certainly don't know of any TVs that come with DVI on them.

There's a fair number of higher-end LCD TVs that had them prior to HDMI becoming popular, and there's a few that still have them. Though, you'd for sure have other things like component or other TV standard connectors.

Do you know what model of display that these screens came in? There's a fair number of sellers on eBay selling digital LCD TV controllers.

Cosmas · 11-26-2008, 06:40 PM

These were not in any end user display. These were purchased directly from the mfg. My company used them for testing with our products. AFAIK, Chi-Mei is not widely used in the entertainment LCD market.

I emailed the guys who made the controller and sent them the spec sheet I posted here. They say its compatible, but didn't say much else. I saw in the spec that it says DE mode is used, but there's no pin connection for it in the diagram. I have a hunch that maybe I need to connect to... something. Maybe one of the incoming pixel channels.

Cosmas · 11-26-2008, 08:59 PM

If someone here had this same setup, how would you wire it? That's what I'd like to know. I'm not even sure that I'm doing the obvious right.

eeguru · 11-26-2008, 10:09 PM

Obvious question. Did you try hooking it up to the odd pairs too? same behavior?

Cosmas · 11-26-2008, 10:24 PM

Yea. I tried all evens, all odds, and then positive evens with odd negatives.

tom61 · 11-27-2008, 01:00 AM

Quote: Originally Posted by Cosmas

These were not in any end user display. These were purchased directly from the mfg. My company used them for testing with our products. AFAIK, Chi-Mei is not widely used in the entertainment LCD market.

Asking whoever was connecting these to your products should be a fairly quick way to find out how it's supposed to be wired.

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