Only concern I have with this approach is latency, you combine latency of the LCD board and then more latency from scaler of the target monitor (since it will not feed native resolution). It should still be sub-frame, at least on the first stage side but both combined may reach half a frame and that starts to become noticable.

Another possible problem is bit depth, you're most probably going to have 18bit temporal dithered signal going to the HDMI chip as LCD panels that actually were 24bit didn't become common until recently (like last 5 years). The Realtek chip does support 24bit output and maybe the HDMI chip can do too so there's one less headache if the firmware can be programmed to enable it.

Things like OSSC etc. are indeed only for low resolution 15KHz RGB from old consoles with bypass for 31KHz RGB (lowest VGA resolution / highest game device resolution). It definitely cannot handle any higher resolutions and it isn't even meant to. Their only job is to turn the unsupported low res video into something higher resolution for PC inputs on newer display devices so that you can actually use things and bypass stuff like deinterlacing that is usually imposed on TV inputs.

However you can use the frontend chip of OSSC and combine it with HDMI transmitter and MCU and create a analog to HDMI/DVI converter, bypassing that FPGA from design as you don't need the scaling. MCU has to program in resolution specific info to get correctly digitized image which is the primary headache with all the cheap converters.

TVP7002 has all of its documentation available and it should be good up to 1920x1080 with reduced blanking, to be within the normal single link HDMI/DVI things 165MHz limit. The ITE HDMI chip can be reused too, though its documentation is less available.

The latency - maybe... It may help to set 1:1 on side of RTD or target monitor
Bit depth - yes, probably BenQ panel was 6bpp, I don't know where the dithering is done if in RTD or LCD panel itself. But the chip could be reprogrammed to TrueColor output. This would be next step after making LVDS2HDMI working.

Dithering is done in the realtek chip, there are several settings for it even wen I skimmed through the datasheet.

I'm not familiar with the chip to know if it can just act as a digitizer without scaler, if it could then this would be even better as (dumb) ADC is what you primarly will need.

Common LCD panels have OSD option to scale image to whole screen or keep 1:1. I don't know about this, I have no longer the LCD panel so I cannot test it now.

BTW how about HDMI lines AC coupling? I have seen some designs like nVidia Jetson where HDMI was AC coupled but other designs and HDMI spec itself claims "DC coupled TDMS..."

that kind of "1:1" I have only seen in laptops, never on a desktop monitor. This won't help here, all the empty pixels are still written (it is not possible to drive arbitrary part on a panel), just different scaling method applied.

HDMI is supposed to be DC coupled but it depends on transmitter. It needs to be able to supply right amount of current to maintain signal integrity and if the transmitter calls for AC coupling you do it that way, otherwise no. This is one place where you exactly follow what datasheet says, there is no room for your own ideas there whatsoever.

The OSSC can digitize and pass through resolutions above 640x480 up to (and including) at least 1600x1200@60Hz (upper limit is probably TVP7002's max capability) .
It just can't line multiply any input resolution greater than 640x480 .

I use an OSSC with my Voodoo 3 and 1920x1200 LCD monitor (which I use in 4:3 mode as if it was 1600x1200).

EDIT : see here Re: VGA Capture Thread for some examples

Aha, OK thanks for info. Just to be clear what you mean by "pass through" - the VGA signal is only digitized and passed out pixel by pixel without any further transformations and processing so no delay introduced... 1600x1200 is good enoug but for my purpose OSSC is quite expansive and I don't utilize FPGA in this case...

RayeR wrote on 2022-02-07, 18:27:

Aha, OK thanks for info. Just to be clear what you mean by "pass through" - the VGA signal is only digitized and passed out pixel by pixel without any further transformations and processing so no delay introduced... 1600x1200 is good enoug but for my purpose OSSC is quite expansive and I don't utilize FPGA in this case...

Yes, I mean digitized with no processing or delay (or a minimal one).

If you don't need the line multiplication, etc, OSSC is indeed overkill .

When I bought my 4k screen (I own LG 27GP950 monitor since June 2021), I thought VGA to DP would be better.
So I bought VC160A and Delock 62596 (in short : VGA => DVI => DP with optional VGA => DVI => HDMI [through passive adapter]).
Also, I recommend getting a two port switcher for ease of use between main PC, and test platform (type depends on needs HDMI/DP).

I use VGA to HDMI as backup (Delock 62408), here's how it looks inside :

PS. Here's my Aten VC160A :

^I can recommend this little thing (I bought it used)

Hope this helps 😀

>agent_x007
Thanks for hi-res photos of those devices. The price of Aten VC160A is similar to OSSC and Delock 62596 still x-times higher than cheap adapters - it's out of my scope. But it's good to see on what chips are they besed on. Not much magic there. IT6613 is HDMI transmitter with parallel RGB input - I already found TFP410 from TI that should do the same. It's paired with some video ADC with parallel RGB output and chained together. My choice of IT6263 was because it takes LVDS input that is much more common in LCD monitors than parallel RGB so I could re-use a half of the circuit.

agent_x007 wrote on 2022-02-07, 19:41:

When I bought my 4k screen (I own LG 27GP950 monitor since June 2021), I thought VGA to DP would be better. So I bought VC160A a […]
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When I bought my 4k screen (I own LG 27GP950 monitor since June 2021), I thought VGA to DP would be better.
So I bought VC160A and Delock 62596 (in short : VGA => DVI => DP with optional VGA => DVI => HDMI [through passive adapter]).
Also, I recommend getting a two port switcher for ease of use between main PC, and test platform (type depends on needs HDMI/DP).

I use VGA to HDMI as backup (Delock 62408)

I'm currently looking for solutions that will help me to properly convert high display refresh rates from vga to dvi/hdmi.

The problem is that I have a high refresh rate monitor Samsung g7, that will accept almost anything over hdmi or dp (including the dvi->hdmi, any weird refresh rates like 88hz or 113hz), but that's when it coming out from modern video cards.

I've got a system where geforce 5700 is installed and I have all sorts of problems with its dvi output. The most it will output is only 75hz (even in 640x480). Anything more and it will revert to 60hz (even though the drivers think it's outputting e.g. 100hz).

So could you kindly test whether your setup gets high refresh rates through? If you have something to test it with. I have a reason to believe the card has some weird dvi implementation and I'll be replacing it but still I'd like to switch to vga and convert the signal myself.

Zoomer wrote on 2023-04-12, 16:36:

I've got a system where geforce 5700 is installed and I have all sorts of problems with its dvi output. The most it will output is only 75hz (even in 640x480). Anything more and it will revert to 60hz (even though the drivers think it's outputting e.g. 100hz).

So could you kindly test whether your setup gets high refresh rates through? If you have something to test it with. I have a reason to believe the card has some weird dvi implementation and I'll be replacing it but still I'd like to switch to vga and convert the signal myself.

I tested Aten VC160A with ARK 2000PV PCI card under DOS with VGASUITE (connected via passive DVI-D/HDMI adapter to my LG 27GP950 monitor) :

Unless you want Windows test as well ?

Hi Guys, Similar to RayeR , I don't have space (London Living). I thought I'd come up with a great solution of using an Aten DVI-I KVM with Audio (CS1784A) that I got off eBay, so I could switch over from my daily driver PC to my retro boxes with ease, but then I realised that Windows 98/older boards generally need PS/2, so I bought a (bloody expensive) Black Box USB to PS/2 Converter (KVUSB-PS2), but I didn't want to buy another Converter for that price (~£100), thankfully I stumbled upon the Aten VGA (CS1732b) KVM, it has a USB only console that nicely daisy chained into the DVI KVM (CS1784A), but supports PC inputs (cables) that support VGA, PS/2 and Audio. Sounds all good...

Unfortunately, I pause my retro shenanigans for up to 6 months at a time and now realise I forget certain issues and don't put 2 + 2 together.

Basically, I have tested the above with a Voodoo 3 which works very well from a display compatibility point of view, but then I now realise that I get blank screen issues (input not supported) using cards like the Radeon 9250 (PCI), Nvidia FX 5700 (AGP) etc.. I first noticed this playing Z (A DOS game by The Bitmap Brothers) as some scenes wouldn't display (I should add Windows @ e.g. 640 x 480, 1024 x 768 etc... seem to work fine), the long story short, it seems the Aten KVMs are altering display modes (e.g. BIOS, DOS Screens/resolutions ) from these cards VGA outputs but its seems to "like" Voodoo card VGA signal (suspect the refresh rate).

@agent_x007 do know if the Aten VC160A is happy displaying various BIOS and DOS-related screen resolutions converted from VGA?

Ironically if I hook up MY FX 5700 via its DVI port the DVI KVM doesn't have these blank screen issues so reverse of your experience.

while writing the above I have gone back and done more testing and these issue are related to compatibility between all three components e.g. Video Card output -> the KVM -> Monitor. I have really old Ezio VGA/DVI LCD (Max 1024 x 768) that I got recently, and if use that instead of my newer monitors (iiyama's that I stupidly bought in 2020 and completely didn't realise that they didn't have DVI inputs) the blank screen issues (input not supported) don't occur using the VGA output of Aten KVM. So its not necessarily the KVM, I guess this is always going to a bit of trial and error, as it wouldn't now surprise me if someone with a Voodoo 3 Card with a different Monitor or KVM now claim they have display issues... the reverse of my experience using the Voodoo card.

After doing this testing, it looks like my best bet and most simple setup (only one KVM) is to get another Black Box USB to PS/2 Converter and a Aten VC160A (if agent_x007 says it plays nice with DOS e.g. resolutions lower than 680x480) .

This might also fix my last bugbear as every thing to the monitor and KVM will be digital/DVI-D using the VC160A. Currently since the Aten DVI-I KVM (CS1784A) has only a DVI-I output and my main monitor(s) doesn't have DVI (actually it looks like most(?) monitors DVI input is DVI-D only, so won't accept DVI-I 's Analog VGA signal/passthrough) I've had to use a splitter (DVI-I to HDMI and VGA) , but for reason unknown this "split" causes the Monitor (GPU/KVM?) to sometimes ignore the HDMI signal/input when switching the KVM between DVI-D and VGA sources... basically I have to faff about to get my dual monitor output on my main daily driver PC working.. seems to be the order in which the PCs are powered/started, but when they won't switch I have to manually disconnect or power down the VGA inputs force a redetect or reboot my main PC which is really annoying.

Sorry for the long read but hopefully this helps someone going down the KVM route facing these or similar issues.

It plays nice with lower resolutions (did NOT checked game you had issues with though), BUT it isn't capable of always making them into 4:3 aspect ratio (so picture get's "stretched", for example 320x200 get's 16:10 ratio). You can somewhat fix this with buttons, but it's too much of a hassle (as you have to do it per resolution change).
Never had issues with picture not showing up on POST with my Aten VC 160A.

I had issues with some older DVI cards not displaying image until driver under windows takes over (mainly Radeon R300 based cards and GF4/FX), but that was due to limitations of DVIs on them (and capture card I used at the time), and neither Component/Composite or VGA outs had the same problem.

EDIT :
If DOS prompt (or Desktop) doesn't show up after exiting a program (ie. "I see a black screen" issue), a reset is required. It is done by pushing one of the buttons on bottom for 5-10 seconds.
Note : Disconnecting external power likely won't reset this adapter, unless both DVI and VGA connections are also teminated (since it is somewhat be powered via VGA, which may prevent it from reseting properly).

Thanks agent_x007, Okay I'll give the Aten VC 160A a try in due course, before you replied and I was looking up the data sheets on the chips on the PCB/Circuit images you provided, the 8-BIT video DAC (VGA -> Digital) the Delock uses is a CAT9883C (CAT9883CCQ-150) and VC 160A uses a Analog Devices AD9983A and both use the ITE IT6613 (HDMI Transmitter) to convert the DAC output to DP/DVI-D. Sadly none of chip spec sheets simply mention resolutions lower than 480i (30Hz) so thanks to you again for your real world feedback. Again to Assist others does the Delock perform as well to the best of your knowledge?

Was looking at the chips to see if they are any cheaper/used alternatives (it wouldn't surprise me that the Delock or Aten is clone of some generic application of the chips) that might have chance at working okay... granted I can't be sure how much firmware and the microprocessor types play a part.

Need to check out VGASUITE as I wasn't aware of such a ready made tester/benchmark. Lasty I think its more an issue with modern screens, converters, switchers (KVMs) more than issues with retro video cards, as I don't recall (used work as an IT field engineer back in the day) these blank screen issues with DOS/BIOS screens on CRTs and (early) LCD from the same era e.g. the old Ezio XGA LCD.