# Internal LCD interfaces, FPD-Link, LVDS, very confused

I feel like I'm stuck in a room with doors all around me and every door I open just confuses me more and answers no questions and even so, I was still hesitant to ask a question because someone is always going to find a reason to basically tell me to google it, even though I have tried and tried and tried and I just simply do not know where to go at this point. I've also tried searching his site and I still have no clear direction. The point of that preface? It was just to hopefully get some understanding...

Edit 2017-04-17: After some info from Journeyman Geek and some further reading, I can summarize what I'm attempting to do at the top here.

In a nutshell, I am trying to take an LCD that uses an unknown interface (CN4 in the PCM-9371 user manual) and have this work with a completely different interface (CN30 in the PCM-9389 manual. This is a single channel 18/24 bit LVDS interface using, I'm assuming, FPD-Link). I'm not sure of much, but I do know that the LCD and the only FPD interface on the 9389 do not have the same language and will have to converted. The biggest problem is that I don't know what interface is being used on the LCD. Even if I can't find a converter, it's possible I could build one. I certainly wouldn't mind the opportunity to learn more. The original question, as well as links to the manuals and more information on the connectors used for FPDs are below. Thanks!

Now then the issue and why I'm so confused.

I have an embedded system using the following board;

Advantech PCM-9371. The user manual can be found below.

The manual specifies three internal ports for displays as such:

Flat panel display connector (CN4) CN4 consists of a 40-pin connector which can support a 24-bit LCD panel. It is Hiroseís product no. DF13A-40DP-1.25 V The PCM-9371 provides a bias control signal on CN11 that can be used to control the LCD bias voltage. It is recommended that the LCD bias voltage not be applied to the panel until the logic supply voltage (+5 V or +3.3 V) and panel video signals are stable. Under normal operation, the control signal (ENAVEE) is active high. When the PCM-9371ís power is applied, the control signal is low until just after the relevant flat panel signals are present. CN4 can connect up to 24 bit TFT LCD.

The only thing I understand from this is that the physical connector is a Hiroseis connector with 40-pins. I'm not sure what is meant by 24-bit LCD and it's apparently just as vague as it sounds because google shows all sorts of results and I don't know which ones are relevant and which ones aren't.

Extension flat panel connector (CN3) CN3 consists of a 20-pin connector which is Hiroseís product no. DF13A-20DP-1.25V. The PCM-9371 supports a 36-bit LCD panel which must be connected to both the CN4 (40-pin) and the CN3 (20-pin). The pin assignments for both CN4 and the CN3 can be found in Appendix C

This apparently is required to be used in conjuction with CN4 if you want to use a 36-bit LCD panel. That makes sense, but not enough to actually help me get a clearer answer.

LVDS LCD panel connector (CN6) The PCM-9371 uses the VIA Twister chip that supports 2 channel (2 x 18 bit) LVDS LCD panel displays. Users can connect to either an 18-bit or 36-bit LVDS LCD with CN6.

This appears to be an entirely different...well everything. Physical connector and interface.

What I am trying to do is upgrade that board to this board;

Advantech PCM-9389. The user manual for this can be found below.

This board only has an LVDS interface and I need to make it so the display that is connected to the old 9371 board via the 24-bit LCD interface works with this. To clarify, the system that I'm trying to upgrade already has an LCD that I would like to avoid replacing if possible, but it uses the 40 pin 24-Bit LCD Flat Panel Connector (CN4) and not the LVDS FPD-Link (CN6).

Ideally I'd just like to better understand the FPD-Link (or whatever it is?) and how this all works but while I know there is plenty of information out there, nothing that I found made me feel confident it was going to actually clearly explain anything to me. I always felt like I was going to waste time reading something that was either unclear, confusing, or just not what I need. So I would really like is if someone could point me to a resource with a very clear directive that I can use to educate myself on this topic. In a nutshell; I have no idea where to start.

...of course, I would also be very happy just to have someone tell me what I need to know as well if that would be easier. Either way, I really just feel so stuck and confused and like I've hit a brick wall.

Any and all help is greatly appreciated!

## migrated from superuser.comApr 16 '17 at 8:27

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• Video connectors are terribly non standard. Oddly the manual suggests both are 20 pin connectors - but the details as I get them are going into an answer – Journeyman Geek Apr 16 '17 at 7:04
• Migrating this to electronics - this feels a LOT more in their wheelhouse. They can kick it back, and folks there probably would be a better fit for the skills you need for this – Journeyman Geek Apr 16 '17 at 8:27
• If you are trying to use the LVDS interface, you will not be able to use the 24-bit TFT display you were previously using. LVDS is a serial interface which operates at a much higher speed than the parallel interface on connector C4. – ks0ze Apr 17 '17 at 17:22
• @Soundfx4, it's certainly possible to convert between the two but if I were doing it I'd just change LCDs to avoid building another PCB. I think this chip from TI should do the trick though (ti.com/product/ds90cf383b) – ks0ze Apr 18 '17 at 13:47
• Cost depends entirely on quantity, time, and where you're willing to source your parts. If you have a small run and don't mind waiting a few weeks you could probably make a PCB interface board for <$30 ordering from dirtypcbs.com. Or, you could by a new LCD from china (aliexpress.com, etc.) for <$10. – ks0ze Apr 18 '17 at 13:59

I'm not exactly an EE, and there's probably a few other implementation details here - but essentially, FPD-Link is a standard protocol that uses LVDS (a specific 'style' of signalling). However the folks at hackaday forum are pretty smart and modder mike's post suggests all you need to worry about is the pin outs which are usually non standard

The 9389 uses a board to board connector (page 13) it seems (so essentially the display snaps into the motherboard) while the 9731 lists connectors that would work for a specific display. In theory they should be protocol compatible

Both of these boards use connectors with the same pinouts - the PCM 9731 has 2 channels with 3 TX pairs each for 6, while the 9389 has the connectors for one of the channels NC or not connected.

The 'bitness' of colour refers to colour depth. Colour depth hasn't changed that much. and the ranges mentioned seem ok.

So, chances are, if you cans scrounge up or make the right cable, yeah, it should very likely work from what I see.

• Hmmm...It looks like...15 and 17 say they are CLK, I suppose for some sort of synchronizing or signals or something? I thought a CLK was necessary for flat panel displays....well at any rate, while they do both seem to have the same pinouts, the system already has a display but it uses CN4, not CN6. I am trying to use the same display without replacing it (not sure if that will be easier or not, but it would likely cost more money) I'm checking out it's pinout now, and looking at that thread you linked. – Soundfx4 Apr 16 '17 at 7:41
• Connector names are arbitrary. CN4, literally means "the 4th connector" and CN6 would be "the 6th connector". I think a lot of the confusion you have is expecting everything to be a standard - when its all non standard. – Journeyman Geek Apr 16 '17 at 7:45
• Oh no, I actually understand that. I'm using the connector name as a reference so you know which one I'm talking about from the manual. And that's the problem with this and why I'm so confused; I am very well aware that there are no standards or at best, loose standards for internal display connectors. But I do know that the display that is in use on the old board is using CN4 which...I have no idea what it's using. While the new board only has LVDS so I can't just wire them in if they aren't speaking the same language. – Soundfx4 Apr 16 '17 at 7:55
• CN4's Pinout, btw, is on 127. I'm looking at it right now and trying to make sense of it. – Soundfx4 Apr 16 '17 at 7:57