VGA/HDMI to LVDS: what chip do they use? - Page 1
Forum section: electronics / general

author: DiTBho
author_rank: Super Contributor
timestamp: April 08, 2024, 12:39:49 pm
content: there are a few cards on ebay that accept VGA or HDMI signals and drive LCDs:what chip do they use?

author: DiTBho
author_rank: Super Contributor
timestamp: April 08, 2024, 12:54:23 pm
content: 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 08, 2024, 02:19:29 pm
content: Adafruit HDMI 4 Piuses Realtek RTD2662, based on the board image on page 4 of thedata brief (in Chinese). There are lots of similar chips, includingST GM5621. The data briefs seem to call these (X-input)LCD Controllers orFlat Panel Controllers. Actual datasheets seem to be very hard to come by.I assume you are aware ofthis 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 theSerializers & Deserializers - SerDescategory. DS90UB940 is MIPI DSI to FPD Link III, and DS90UB941 is FPD Link III to MIPI DSI.

author: DiTBho
author_rank: Super Contributor
timestamp: April 08, 2024, 02:38:02 pm
content: Quote from: Nominal Animal on April 08, 2024, 02:19:29 pmI remembered that "HX6810-A IC, no datasheet to be found so far, but please do keep looking"

author: DiTBho
author_rank: Super Contributor
timestamp: April 08, 2024, 02:51:11 pm
content: 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?mumbleI 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

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 08, 2024, 08:45:51 pm
content: 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.

author: DiTBho
author_rank: Super Contributor
timestamp: April 09, 2024, 08:08:36 am
content: Quote from: SiliconWizard on April 08, 2024, 08:45:51 pmAnia 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 hwbut 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 thegm5621 product briefQuotewhat 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 shiversso ... so was there really a need to mention it in the PDF of an LCD controller?!? .. thanks ST!!!)

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 09, 2024, 08:21:06 am
content: 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.

author: DiTBho
author_rank: Super Contributor
timestamp: April 09, 2024, 08:37:36 am
content: Quote from: SiliconWizard on April 09, 2024, 08:21:06 amumm, in addition to the fact that it consumes more electricity

author: DiTBho
author_rank: Super Contributor
timestamp: April 09, 2024, 09:00:17 am
content: 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 impossibleSo 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 09, 2024, 09:37:34 am
content: Quote from: DiTBho on April 09, 2024, 09:00:17 amncurses you can fix by adding the new format to terminfo, if even remotely similar. Then, you just set theTERMenvironment variable naming the entry. Not everything needs to be ANSI/DEC/VT/XTERM compatible...Quote from: DiTBho on April 09, 2024, 09:00:17 amI 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.

author: DiTBho
author_rank: Super Contributor
timestamp: April 09, 2024, 11:28:31 am
content: Quote from: Nominal Animal on April 09, 2024, 09:37:34 amfor 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.Quote from: Nominal Animal on April 09, 2024, 09:37:34 amYup. I'll try to buy some chip, and boards, then study the doc, and see how it goes

author: amyk
author_rank: Super Contributor
timestamp: April 12, 2024, 12:29:55 am
content: 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.

author: DiTBho
author_rank: Super Contributor
timestamp: April 12, 2024, 09:37:45 am
content: Quote from: amyk on April 12, 2024, 12:29:55 amAh-Ha!!! I knew that thing smelled too much like CPU/MPU.In one of those monitors, someone sticked a "intel-inside" stickerand guess what? I bet there is an 80186 inside, LOL(x86 haunts me, the more I try to stay away from it, the more I find it under my feetunder my desk (Geode thinclient) .... inside the weather station (80186), inside the NAS (i5), and now, even inside the monitor!!!one way or another)