MiST VGA Compatibility

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Re: MiST VGA Compatibility

Postby Higgy » Wed May 17, 2017 11:18 am

I have a BL912 also. I got it over the 7?? because the 912 also has DVI so I can use HDMI.

On my actual AMIGA 1200 there is some interference/patterns in the picture, but it is perfect with FPGA devices. And yes it is good to have a ratio close to 4:3!

I have been meaning to make a SCART adaptor to use it with all my original hardware. Especially as you say it accepts composite sync.

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Re: MiST VGA Compatibility

Postby DrOG » Wed May 17, 2017 1:28 pm

Did you try to fine tune the 'pixel clock' and 'phase'?
I found the recommended values for Amiga here (at the bottom 1/3 of the page):
http://eab.abime.net/showthread.php?t=80217&page=2

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Re: MiST VGA Compatibility

Postby DrOG » Thu May 18, 2017 4:32 am

Hi all!

Just tried the BenQ BL912 with sync-on-green RGB and YPbPr signals, but it didn't work, despite the rumors.
Sou you need at least a separated composite sync signal to get a picture.

I'm planning to build a SCART->VGA atapter, as Higgy said to use it with standard SCART out devices (i.e. DVD-player, Set Top Box etc...).

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Re: MiST VGA Compatibility

Postby DrChaos » Thu May 18, 2017 10:04 am

Wouldn't it be more straightforward to use VGA/VGA for the Mist instead of SCART? I was thinking of building one with two inputs, Scart and VGA. Still think if it is possible to have a VGA/VGA with the Sync Cleaner that can be switched off/on to have only one cable for all cores...

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Re: MiST VGA Compatibility

Postby DrOG » Thu May 18, 2017 1:14 pm

In the case of this BenQ, you don't need anything more than a standard VGA cable.

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Re: MiST VGA Compatibility

Postby DrOG » Sat May 20, 2017 5:30 am

Just finished and tested my SCART->VGA adaptor for the BenQ BL912.

I used a VGA male for the monitor and a SCART female on the other end, between them a 9-lead wiring as follows:

VGA_SCART_function
1-------15-------RED
2-------11------GREEN
3--------7-------BLUE
5-------17-------GND
6-------13------R GND
7--------9------G GND
8--------5------B GND
10------18-------GND
13------20-----C SYNC

I didn't solder VGA pin 14 to SCART pin 16, it's unnecessary, but it works in case if it's connected also.
Perhaps not every grounds are necessary, but I wired all of them for safety's sake.

It works perfect with MIST, Turbo Chameleon 64 and Enterprise 128. But it doesn't work with my old Yamada DVX-6700 standalone DVD player. I think the problem is that the device emits a full composide video signal instead of pure CSYNC, even if I set the SCART output from AV to RGB in the menu (tested with SCART->3xRCA cable).

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Re: MiST VGA Compatibility

Postby Orky » Thu May 25, 2017 9:41 pm

Hey DrOG,

Just wanted to say thanks for the info about the BenQ ordered one a couple of days back and it's resolved all my screen issues :)

Cheers

-Si

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Re: MiST VGA Compatibility

Postby DrOG » Fri May 26, 2017 11:18 am

You're welcome!

I'm planning to build a sync separator, following one of the tutorials below:

http://www.mmmonkey.co.uk/composite-syn ... er-lm1881/
http://retrorgb.com/syncstripperchiponly.html

My plan is to use this BenQ with older devices also (i.e. standalone DVD-player).

Further useful links:
https://ianstedman.wordpress.com/2016/0 ... o-engines/
http://www.retrogamingcables.co.uk/comp ... osite-sync

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Re: MiST VGA Compatibility

Postby Orky » Fri May 26, 2017 5:00 pm

I just submitted a pull request that fixes the viking 1280x1024 mode on this and my dell screen.

Maybe useful if you use that feature.

-Si

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Re: MiST VGA Compatibility

Postby DrOG » Sat May 27, 2017 3:11 am

Thanks, I used the ST core for playing only Lords of Chaos so far (I'm big fan of Julian Gollop's early games, beginning from Rebel Star, through Laser Squad and Lord of Chaos, and finally the UFO). I prefer the Amiga version, but it's treasure maps has graphic glitches on level 4, so I had to complete the previos levels also ;-)).

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Re: MiST VGA Compatibility

Postby Higgy » Sun Jun 04, 2017 7:52 pm

Hi DrOG.

I got my BL912 adaptor cable all sorted. MiST is great (although for me MiST-SCART to SCART-VGA BenQ is not that useful as nearly all MiST Cores output RGB/VGA).

My test hardware for BenQ SCART input is a Mk1 Megadrive. I had a spare sync stripper chip around so made up a cable. The monitor keeps selecting colour as YUB (or whatever) so you need to select RGB each time which is annoying. It works without needing VGA pin 14 connected. So just composite sync I am not using the additional Vertical Sync signal.

I get vertical banding, just like with my real AMIGA.I think the colours are also wrong. On Italia 90 football game grass is green but skin is blue!.

One strange thing I have a Micky Mouse game and the monitor pops up a 'suggested resolution' notice and won't display anything? Odd.

I region modified my Megadrive so it should be either 60Hz NTSC or 50Hz PAL. I don't know if this makes a difference but my Megadrive SCART lead has various resistors and capacitors on the colour signals. But for me the BenQ has to work with all my stuff. I am not modifying or creating special SCARTS for BenQ use.

How you getting along?

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Re: MiST VGA Compatibility

Postby DrOG » Mon Jun 05, 2017 6:33 am

@Higgy:
Briefly: I experienced the same. But here are the details...

Yesterday I finished my sync stripper, and experimendet a bit.
I modified a standard SCART cable, so built this circuit small enough to fit into a SCART plug's housing, as it's recommended to put it as close as possible to the video signal's source.
This is a more or less universal solution, I can plug the other end into the above mentioned SCART->VGA adaptor if I want to connect it to the BenQ, and leave it out to use it with sandard SCART input devices.

I tested it with my 13-years-old Yamada DVX-6700 as signal source. It was one of the first DivX-compatible standalone DVD-players. Actually this is my only device at home which outputs RGB + composite video instead of pure csync.
I used basically the standard schematics, with minor modifications (picture attached to this post).

1. The power supply:
On some forums they recommend to feed the LM1881 IC directly from SCART pin 8, which should have work theoretically, as the standard voltages of this pin are 5-8V at 16:9, and 9.5-12V at 4:3 aspect ratio, and the IC needs 5-12V. I tried it, but didn't work: On my main TV, a Samsung LE40B650 the picture was too bright, distorted and unstable. The BenQ's screen remained black. Instead of the former mentioned manner giving 5V to the IC using a standard USB phone charger solved the problem.

2. The 75 Ohm resistor between the composite video input and ground:
Some sources recommend it: "It should include a 75 ohm (or thereabouts, the value isn't critical) resistor between the input and ground, before the coupling capacitor. This sets the optimum video level and combined with the lower line impedance and reduced noise, give the LM1881 a much better chance of seperating the sync from a video signal which is changing from bright to dark rapidly." I tested it mostly with static images, but it's absance or presence didn't do any visible difference in regard of picture quality. I left it there because I was too lazy to remove it, and I think it won't harm anybody ;-)) .

3. The value of the resistor on composite sync output (R1):
Different authors - different recommendations again. Some say it's not necessary at all, some to use a 330-470/270-510 Ohm impedance in case of SCART, and 680-820 Ohm in case of VESA monitors. I tried the circuit first without this resistor, and the picure of BenQ had a strong greenish tint. Next I tried a 750 Ohm impedance, the result was better, but still green shaded. After it used 1K value, again strong green tincture. The best result was with using 470 Ohm, that effected quite good white balance, but the red is still a bit weak (I would call it strong orange).

I tried the DVD-player with PAL settings, and had to choose the RGB colour format manually, as the monitor identified it as YPbPr.
On the Samsung TV there wasn't visible difference in aspect of picture quality using different values of R1 resistor.
After it worked acceptable with BenQ (a bit blurry picture, but it's not surprising, the source is an 576i signal), I tested the separator on the TV, and the only visible effect was that the picture got darker if using it, otherwise the image looked the same. Don't know if on older CRT's would be any major improvement or not, didn't try it so far.

@Higgy again:
"I get vertical banding, just like with my real AMIGA..."
Did you try to set the pixel clock manually? On other forums members recommend values near 90, i.e. 94, as they say this will completly eliminate vertical banding. The exact value may vary using different Amiga models, i.e. on the Amiga 500 they had to adjust the pixel clock to exactly 88 and Phase to 30 and got a crystal clear image with no vertical lines. On A1200 on the other hand they ended at pixel clock 92 and Phase around 30. this will vary a bit from model to model also: Some had to put their pixel clock to 88 and Phase clock to 30 + to get a perfect picture, even though 90 was the recommended pixel clock for Amiga use. Also seen others needed other values like 92. I think it worths to try different values.
I dont' have an Amiga (yet), so cannot test it by myself.
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Re: MiST VGA Compatibility

Postby Orion_ » Mon Jun 12, 2017 1:20 pm

I just got an ST mini (mist clone) and I'm a bit disappointed by the video output too ..
I was hoping to get a pixel perfect output but I get scaling which is ugly.
I tried the latest firmware and latest ST core on 4 different VGA monitor, on my Sony TV it says that the video signal is wrong, and on my 3 others VGA monitor I get ugly scaling, 2 are 16:9 (Viewsonic 2231wa, Viewsonic 2014w) and the last one is 5:4 (Acer V176L bm)
PAL 56 or 50 mode won't change anything to the scaling ugliness.

Would I need something like a Multisync capable lcd monitor to get accurate "pixel perfect" output ?
do you recommand any specific model ?

Or is preferable to get an RGB scart cable to get accurate video on a real TV ?
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Re: MiST VGA Compatibility

Postby Orion_ » Mon Jun 12, 2017 3:14 pm

I don't quite understand, I see that, most of cores says "PAL mode is 720x576p @50hz"
that is 5:4 resolution, then why I have bad scaling on my 5:4 monitor ?
does the Atari ST video core use this video mode too ?

the other core such as the C64 and PlusToo are working great without much scaling issue.
I guess the Amiga one also works (didn't tried to much that one)

Here is a closeup photo of each video mode I tried, this is the best result I can get, even when tweaking the monitor horizontal position/clock/focus
PAL 50hz
Image

PAL 56hz
Image

mono
Image

I got the 1280x1024 highrez mode working but only with manual monitor horizontal tweaking, which I must do each time, this is annoying
any good VGA monitor that someone can recommand for the mist that can get the MiST resolution pixel perfect ?
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Re: MiST VGA Compatibility

Postby eeun » Mon Jun 12, 2017 4:37 pm

If you really want 'pixel perfect' get a CRT VGA monitor. Bulky old energy hogs, I know, but the picture they produce with MiST is better than anything I've seen on various LCDs, and much closer to what you'd see on the original systems.

But if you prefer the LCD route, I've had very good results with Samsung monitors. 920N & 715V models both handle the 50/56/60 modes well. Still not perfect, but better than the crappy 17" Dells that make up a chunk of my collection. There;s a thread somewhere here noting various other models that are MiST-friendly.

I find 25% scanlines on the supporting cores helps compensate for LCD scaling.

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Re: MiST VGA Compatibility

Postby Orion_ » Mon Jun 12, 2017 5:17 pm

I think I need to find a good VGA monitor with "no scale" option, meaning if the resolution is smaller than the native one, it will display black bars around the image and make it pixel perfect.
if anyone now an LCD monitor who can do this, please tell me :)

it seems to be the "aspect" option "1:1" but this option is rare to be found, only on pro monitor at >= 300€ :/
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Re: MiST VGA Compatibility

Postby DrOG » Tue Jun 13, 2017 4:15 am

My results with the BenQ BL219 (used only the 'auto' option, didn't set the geometry of picture manually):

50Hz VGA:
Image
Ugly scaling, but no borders.

56Hz VGA:
Image
Ugly scaling with a narrow black stripe at the top & bottom of the screen.

Mono VGA:
Image
Ugly, but perhaps somewhat better scaling, black borders around the picture.

50Hz SCART
Image
A bit blurry image (interlaced signal!) with black borders around it.

I agree with eeun, the best solution is a CRT monitor! You can try older CRT TVs with minimig-to-scart cable also, perhaps this would be the most authentic way...

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Re: MiST VGA Compatibility

Postby Orion_ » Tue Jun 13, 2017 7:38 am

in your screen menu, try to change the "display mode" to "Aspect", see if it gets any better ?
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Re: MiST VGA Compatibility

Postby DrOG » Wed Jun 14, 2017 3:59 am

Hi All!

Yesterday I tested the NES core on my monitor for three reasons:

1. It's known to be problematic: has a badly (very left) centered image on most screens.
2. It's an NTSC core - tested only PAL sources so far.
3. It supports YPbPr/YUV output over VGA connector, thanks to Sorgelig!

It supports interlaced mode (scandoubler_disable=1) as well.
During my tests I used a standard VGA cable to connect the MIST to my BenQ BL912.
I used only 'auto' option, and didn't modify the picture's geometry manually.
I had to switch the colour format from RGB to YUV myself, because the monitor didn't identify it automatically.

Here are my results:

NES_VGA_progressive
Image

NES_VGA_interlaced
Image

NES_YUV_progressive
Image

NES_YUV_interlaced
Image

And the conclusions in some words:

1. There are black stripes on the left and right sides of the picture. These are wider in case of interlaced signal source.
2. The picture is well-centered.
3. The image is a bit blurry if scandoubler is disabled (we already knew that).
4. The white balance is not exactly the same: the picture is a bit reddish using YPbPr compared to RGB.

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Re: MiST VGA Compatibility

Postby eeun » Fri Jun 16, 2017 6:55 pm

Interesting comparing the various outputs. Thanks for sharing that!

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Re: MiST VGA Compatibility

Postby DrOG » Sat Jun 17, 2017 3:13 am

You're welcome!

I compared earlier the different output modes using my Samsung LE40B650 in another topic as well:

viewtopic.php?f=101&t=31006&start=25

As Sorgelig wrote, every display is different in aspect of signal handling, and a given device may also produce diverse results depending on the used input.

I'm planning to build a new sync stripper, which generates separated horizontal and vertical syncs instead of composite. As I couldn't obtain the necessary EL1883 or EL4583 IC, I will build one with the well-known and popular LM1881N, combined with another IC containing logical gates, which will create the missing H-sync from the C-sync and V-sync signals. I ordered it's components, but didn't arrive so far.

See schematic below.
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Re: MiST VGA Compatibility

Postby DrChaos » Wed Jun 21, 2017 6:59 am

I still hope that some of the Core Developer will enable a switch to use clean sync in the 15Khz Core, but I guess the number of people using Multisync VGA is rather small. Unfortunately due to my lack of programming skills I am unable to contribute on that side...

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Re: MiST VGA Compatibility

Postby DrOG » Wed Jun 28, 2017 1:39 pm

I tried the schematic 2 post above, but it didn't work...

Being a second LM1881N on hand, built another sync stripper with minor modifications:

1. This time I used a SCART male connector (it contains the circuit itself) and a standard VGA cable, cutting off one of it's plug.
2. Composite sync out goes to VGA pin 13 (horizontal sync), without resistor.
3. Vertical sync straight to VGA pin 14.
4. GND to VGA pins 5 & 10.
5. Used a (third) 0,1uF decoupling capacitor between GND and +5V.

I think it's even more universal, but still not 100% compatible solution for connecting composite video sync out RGB devices to VGA input displays.

More info here: http://www.epanorama.net/faq/vga2rgb/vgamonitor.html

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Re: MiST VGA Compatibility

Postby DrOG » Mon Jul 03, 2017 5:04 am

Hi All!

I tested consequently all the cores avaiable on the MIST with my BenQ BL912, and made some conclusions:

1. This display is (almost) omnivorous: the only core which exceeded it's abilities was the ZX01. Black screen in scandoubler enabled and disabled mode as well. My old Belinea CRT has glitches also when using this core, both in PAL and NTSC modes, on both sides near the top of the picture:

Image

Image

2. It tolerates low refresh rates well: although it's specification writes "Vertical input frequency: 55-76 Hz", works with much lower frequencies also:

-2 cores have 56Hz refresh rates: Atari ST in PAL 56 mode, and Videoton TVC VGA version, both works flawless (as far as I know this is the lowermost limit of standard VGA vertical frequencies, but i.e. my Samsung LE40B650 doesn't support it):

Image

Image

-Every PAL core has 50Hz output frequency (except Elektronika BK-0011M, which is only 49Hz - my LG L1734S refuses it, 'out of range'). The BenQ hasn't such problem.

Image

-I found one very non-standard core, Gehstock's 'pacman(RGB Output Test#2).rbf', which uses 720x288@43Hz, and it's still fine for the monitor:

Image

3. Sometimes it identifies incorrectly the colour format in 15KHz mode: only 2 cores are affected so far (SMS and MSX), and using my sync stripper with a composite out RGB device, there's the same issue. It's an annoying but manageable problem, since there's an option in the monitor's menu to change the color format manually from YUV to RGB.

4. Sometimes NTSC output is 640x500 instead of 640x480: the C64, PC Engine and Colecovision cores show this phenomenon:

Image

Image

Image

5. It has not problem with unusual resolutions, manages well these absolutely non-standard values:

In case of Acorn Archimedes, during boot the messy red screen is 720x288@75Hz:

Image

Desktop is usual 640x480@60Hz, but starting games it switches to 720x400@70Hz:

Image

And in '64Hz Mono' mone (pressung key 2 on numpad during boot) it's 1600x900@65Hz:

Image

The Amstrad has an extraordinary 73Hz refresh rate at 800x600 resolution (72 or 75 Hz would be standard):

Image

Some arcade cores are affected also: Donkey Kong, 640x500@62Hz (it has several graphic glitches also):

Image

And finally some nice interlaced 'solutions' (in these cases there might be a sync issue, as the cores below are not compatible with standard minimig-VGA-to-scart cable, and their resolution is 720x2??@??Hz. I think these are not real interlaced, but instead progressive signals with the half of the height?):

TRS-80(L2)-720x288@60Hz:

Image

FPGAPCE-720x240@59Hz (It's an interesting case, as it has an original and a modded version, the latter is more compatible, but still not 100% perfect, and has issues with several screens):

Image

And see the earlier mentioned Gehstock's 'pacman(RGB Output Test#2).rbf' also.

In normal case the monitor would indicate only the number of lines, the 'i' as interlaced and finally the refresh rate, i.e. 480i60/576i@50, see the Atari ST PAL mode for reference:

Image

That's all so far.

I hope my experiences will help to developers correcting bugs and purchasers who are looking for a compatible monitor (you can pick up the non-standard cores to an SD-card and go for shopping equipped with the MIST, testing the display before buying it).

Regards: Gábor

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Re: MiST VGA Compatibility

Postby ericgus » Mon Jul 03, 2017 6:13 am

Iv also had really good success with the Samsung Syncmaster 715v .. I don't think I have tried a core on it that didn't work .. even the hard to display PlusTOO core worked fine..


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