Author Topic: VGA/HDMI to LVDS: what chip do they use?  (Read 3304 times)

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Offline DiTBhoTopic starter

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VGA/HDMI to LVDS: what chip do they use?
« on: April 08, 2024, 12:39:49 pm »
there are a few cards on ebay that accept VGA or HDMI signals and drive LCDs:

what chip do they use?  :-//

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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #1 on: April 08, 2024, 12:54:23 pm »
I mean, what "chip do they use" to convert VGA (or HDMI) into "FPD-Link" a serial protocol, which transmits parallel data { R, G, B, HSync, VSync, DataValid } serially.

E.g. using a 6-bit LCD panel, 6-bits per color channel { { R0..R5}, { G0..G5 }, { B0..B5 }, VSync, HSync, DataValid } are transmitted using 3 LVDS lanes and 7:1 serialization.
« Last Edit: April 08, 2024, 12:56:12 pm by DiTBho »
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Offline Nominal Animal

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #2 on: April 08, 2024, 02:19:29 pm »
Adafruit HDMI 4 Pi uses Realtek RTD2662, based on the board image on page 4 of the data brief (in Chinese).  There are lots of similar chips, including ST GM5621.  The data briefs seem to call these (X-input) LCD Controllers or Flat Panel Controllers.  Actual datasheets seem to be very hard to come by.

I assume you are aware of this Hackaday project log?

Mouser sells TI DS90UB949 serializers (HDMI to FPD Link III) and DS90UB948 deserializers (FPD Link III to LVDS/OpenLDI); you'll find these in the Serializers & Deserializers - SerDes category.  DS90UB940 is MIPI DSI to FPD Link III, and DS90UB941 is FPD Link III to MIPI DSI.
 
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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #3 on: April 08, 2024, 02:38:02 pm »
I assume you are aware of this Hackaday project log?

I remembered that "HX6810-A IC, no datasheet to be found so far, but please do keep looking:-//
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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #4 on: April 08, 2024, 02:51:11 pm »
More than anything I wonder: what's inside those Chinese chips? an MPU? coupled with dedicated ASIC and an output stage seen in Zynq's TMDS33 outputs?
A TMDS type thing (used by DVI/HDMI) with an open drain differential standard terminated at 3.3V at the receiver end?

mumble  :-//

I think of an MPU, because some of those cards show a logo at the start, in addition to the fact that they also show a menu, where it is possible to set some screen characteristics, such as moving the screen a little to the right, left, up , low, widen it, narrow it, center it, etc
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Online SiliconWizard

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #5 on: April 08, 2024, 08:45:51 pm »
Nah, they are dedicated ICs. There are many out there - the issue is that these are often hard to source (if at all possible) in small quantities, ditto for getting ahold of datasheets.
 
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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #6 on: April 09, 2024, 08:08:36 am »
Nah, they are dedicated ICs. There are many out there - the issue is that these are often hard to source (if at all possible) in small quantities, ditto for getting ahold of datasheets.

Ania implemented Zoom from 320x240 to VGA (640x480) by repeating the last bit twice, so she attached a small fpga coupled with a R-DAC to my old Palm PDA STN LCD digital lines and now the PDA has VGA output.

so I guess "Zoom scaling" (from VGA) and "shrink" (from WUXGA) are both doable in hw  :-//

but even so, how can those chips manage the setting-keyboard, menus and booting-logo?
ok, Ania created a whole VT100 in HDL, and it works without any CPU, but some of those chips also have IR controller, and isn't this a clue they have a small MPU inside?

In any case, I read weird things from the gm5621 product brief
Quote
In addition, GM5621/5626 include an integrated x86 OCM with SPI compatible interface, a
multicolor proportional font OSD engine, a programmable coefficient scaling engine, dual
channel Schmitt and Reset circuitry. Along with high quality and reliability, GM5621/5626
also provide a very low cost system design by reducing the number of components and the
reduction in the board size.

what the frog is an "integrated x86 OCM" ?!? why x86 should be mentioned there!?! ARG!!!
(
x86 is my worst nightmare, I'm terrified of it, when someone mentions it to me, I get shivers
so ... so was there really a need to mention it in the PDF of an LCD controller?!? .. thanks ST!!!
)

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Online SiliconWizard

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #7 on: April 09, 2024, 08:21:06 am »
It is doable with a FPGA of course, but it's definitely some work.
Rescaling in real time, apart from trivial factors, is not easy either. But if it's just an integer factor, or of the form integer+1 half, then it's relatively straightforward in HDL using just repeated values (in the first case) or very simple fixed point (in the second).
Supporting more than exactly one configuration (one interface type to one another, for one source resolution and one destination resolution) is going to be a mess quickly.

I've used this kind of boards, but have honestly never had a close look at the ICs they were using. Possibly they embed a small processor core for handling menus and whatnot. Something you could also do in FPGA. I don't think it's worth the trouble.
 

Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #8 on: April 09, 2024, 08:37:36 am »
FPGA. I don't think it's worth the trouble.

umm, in addition to the fact that it consumes more electricity  :-//
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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #9 on: April 09, 2024, 09:00:17 am »
Small parenthesis about "fbga" and "vt100" ...

In the end I also participate in the Ania's project, and we redesigned the entire protocol from scratch.

Supporting the original vt100  is feasible but very burdensome in terms of design and testing hours, already with vt220 things get bloody worse, and adding functionality becomes practically impossible

So the new terminal is no more "vt100-100%-compatible" but "vt-like", which breaks the compatibility with the standard /bin/getty and /lib/libncurses, but it's awesome as on thre HDL side, it simplifies the state machine that describes the engine by several order of magnitude, and helps introducing compression, bitmap, vectors, and other useful features!

Up to now Ania and I have used one of those Chinese boards that converts VGA to LVDS, but we would like to better integrate everything into a smaller case with an LCD, or even just redesign the entire motherboard "all in one" with one of these chips, as long as it is documented and not "electricity hungry" (we are on battery)

The hardware we made has a VGA R-DAC, so "analog RGB" & "digital H V" (this makes it compatibile with external VGA PC monitors, which is great for debugging), but there are also 5 bit digital RGB signals @25-65 MHz pixel clock.

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Offline Nominal Animal

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #10 on: April 09, 2024, 09:37:34 am »
breaks the compatibility with the standard /bin/getty and /lib/libncurses
ncurses you can fix by adding the new format to terminfo, if even remotely similar.  Then, you just set the TERM environment variable naming the entry.  Not everything needs to be ANSI/DEC/VT/XTERM compatible...

Up to now Ania and I have used one of those Chinese boards that converts VGA to LVDS, but we would like to better integrate everything into a smaller case with an LCD, or even just redesign the entire motherboard "all in one" with one of these chips, as long as it is documented and not "electricity hungry" (we are on battery)
I think your best bet would be Realtek RTD266X, considering it is used by Adafruit and Pimoroni for similar stuff.

Getting hold of sufficient documentation to implement the board and program the darn thing will be the biggest hurdle, I believe.
 

Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #11 on: April 09, 2024, 11:28:31 am »
ncurses you can fix by adding the new format to terminfo, if even remotely similar.  Then, you just set the TERM environment variable naming the entry.  Not everything needs to be ANSI/DEC/VT/XTERM compatible...

for now, as application, we only have a test-bench and a text-editor (like Nano/Joe), both linked to a custom library that manages the vt-term at the low level.

I think your best bet would be Realtek RTD266X, considering it is used by Adafruit and Pimoroni for similar stuff.

Getting hold of sufficient documentation to implement the board and program the darn thing will be the biggest hurdle, I believe.

Yup. I'll try to buy some chip, and boards, then study the doc, and see how it goes  :-+
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Offline amyk

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #12 on: April 12, 2024, 12:29:55 am »
They are called scaler boards, basically the same thing as in a monitor.

The GenesisMicro ICs do have an 80186 as their embedded controller. Others tend to use 8051 or 6502.
 
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Offline DiTBhoTopic starter

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Re: VGA/HDMI to LVDS: what chip do they use?
« Reply #13 on: April 12, 2024, 09:37:45 am »
They are called scaler boards, basically the same thing as in a monitor.

The GenesisMicro ICs do have an 80186 as their embedded controller. Others tend to use 8051 or 6502.

Ah-Ha!!! I knew that thing smelled too much like CPU/MPU.
In one of those monitors, someone sticked a "intel-inside" sticker

and guess what? I bet there is an 80186 inside, LOL  ;D

(
x86 haunts me, the more I try to stay away from it, the more I find it under my feet
under my desk (Geode thinclient) .... inside the weather station (80186), inside the NAS (i5), and now, even inside the monitor!!!
one way or another
)
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