VOGONS


First post, by clb

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Hi all,

I recently got an OSSC converter for VGA -> HDMI. Pairing that with my BenQ BL3201PT 32" 4K display. https://www.displayspecifications.com/en/model/df62527

OSSC upscales the signal to proper VGA aspect ratio with 5:6 pixels, which is great. I get pillarboxes on left and right of the 16:9 display, forming a 4:3 output. Sweet!

Since OSSC is a scanline level converter, it does not convert refresh rates. On one of my retro PCs, DOS text mode comes in to OSSC VGA input as

Horizontal refresh: 31.46kHz
Vertical refresh: 70.08 Hz
Mode: 419-p
OSSC detected sampling settings: H. samplerate=2000, H. s.rate frac=.00, H.synclen=237, H.backporch=120, H.active=1600, V.synclen=2, V.backporch=34, V.active=400, Sampling phase=180deg

And what goes out to the HDMI display from OSSC is 1600x1200@70Hz.

To a positive surprise, this was not a problem to BenQ BL3201PT: it happily accepts the 70Hz HDMI input video signal - though it does seem to frame-drop it to the 60hz panel, not actually running the panel at 70 Hz. This does cause visible stuttering in panning motion, well observed in e.g. Supaplex that pans the whole game area as one moves.

That is a small nuisance, but something I can live to accept.

However, big problems start with my other retro computer I recently restored, a MikroMikko 4 TT m326. There is an integrated Paradise video card on the motherboard (and I cannot run an external ISA video card on it looks like, won't boot). As a big surprise, the Paradise card generates a non-standard display mode immediately at boot for DOS text mode. OSSC does pick that signal up with no problems, and identifies it as:

Horizontal refresh: 44.55kHz
Vertical refresh: 87.02 Hz
Mode: 512-p
OSSC detected sampling settings: H. samplerate=800, H. s.rate frac=.00, H.synclen=96, H.backporch=48, H.active=640, V.synclen=2, V.backporch=33, V.active=480, Sampling phase=180deg

But the issue is that my BenQ will not accept that refresh rate, but complains "Out of Range". 🙁

When I plug the VGA input in to the original 14" CRT that came with the computer, it does produce a regular 80x25 VGA text mode at DOS boot, so the computer does produce a proper signal.

Now I'm not sure what to do about this. The options that I am pondering about:

1) Get another VGA->HDMI converter. I do already have this cheap "DeLock" one: https://www.delock.com/produkt/62460/merkmale.html . Unfortunately that does not work at all on either PCs (not for 70Hz or 87 Hz text mode). Do such frame rate converting adapters exist?

2) Get another LCD that supports higher refresh rates, like 120Hz. I actually do have an ASUS gaming display with 144Hz support, but it seems to be very picky with its supported input resolutions, maybe due to being a G-Sync panel, or just due to being a gaming display, or just due to being ASUS. The BenQ BL3201PT is advertised as a "Pro"/Business display, and it seems to be very compatible with input resolutions and refresh rates I have thrown at it: it can take in a 320x240@60Hz HDMI input signal from Raspberry Pi without complaints.

I wonder if I tried a high refresh rate "gaming" display from BenQ (they don't seem to have high refresh rate "pro" displays, high refresh are all gaming oriented), if that might have better success with 87Hz HDMI signal?

Or I wonder if I should try one of those displays that have a 75Hz panel and also take in VGA natively? E.g. https://www.msi.com/Business-Productivity-Mon … 1/Specification . Although that one is just 1920x1080, so it cannot perfectly upsample 320x200 -> 1600x1200. Maybe those might have been designed a bit more with VGA in mind, and would accept the 87 Hz HDMI from OSSC.

Can you recommend what might be good LCD displays for this purpose? Do you know of a great compatible LCD for DOS?

3) I would really like to avoid having to add a CRT. But if there is no LCD based solution possible for 87Hz input, maybe I should just bite it and make room in my apartment for a CRT. That raises the question - what is a good CRT for DOS gaming? I would be looking for one that is large enough to comfortably view, preferably ~19" at least. Is there a CRT display model that is known to be great for DOS? Reading other threads on this topic, Sony Trinitrons seem to be very liked.

I am currently primarily interested in 386 and 486 era, with compatibility with various refresh rates for demo viewing, though supporting higher VESA resolutions would certainly be a bonus. I don't mind seeing the pixels, I like them.

Thanks for any tips you might have!

Reply 2 of 22, by darry

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You are lucky that your OSSC works at 1600x1200@70Hz without artifacts as that mode, with those timings, (sampling at 2000 on horizontal with line3x vertically) is significantly out of spec for the OSSC itself.

That non standard VGA mode on the Paradise seems like it would likely not have worked on a standard VGA-only (non SVGA) CRT either . It seems odd as a default settin, as it is definitely non standard and is likely to cause weird issues even on a compatible CRT with software expecting 70Hz . Is there a modesetting utility for the Paradise card that can be run, possibly with an option to save settings to an onboard EEPROM ?

Reply 3 of 22, by clb

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darry wrote on 2021-07-24, 10:59:

Is there a modesetting utility for the Paradise card that can be run, possibly with an option to save settings to an onboard EEPROM ?

I am not familiar with such - at least the original PC did not have any that I would know of. For more information, the PC is from 1990+- 1 year, before VESA support. Attached a photo of the graphics chip integrated on the system backplane. It has the text

(C) Paradise '88
PVGA1A-JK
00-02 9035
020092121402

Reply 4 of 22, by darry

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Just a thought, have you tried connecting the Paradise VGA directly to your Benq's VGA input ? Maybe the OSSC is somehow misdetecting or synching improperly with that card .

Reply 5 of 22, by maxtherabbit

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the PVGA1A is a bog standard VGA ASIC, it should not be producing bizarre non-standard text modes unless the video BIOS is programming it to do so

Do you have any secondary way of verifying what timings are coming out of the card? Scope, logic analyzer, frequency counter, OSD on the CRT, etc. ?

Reply 6 of 22, by clb

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darry wrote on 2021-07-24, 13:46:

Just a thought, have you tried connecting the Paradise VGA directly to your Benq's VGA input ? Maybe the OSSC is somehow misdetecting or synching improperly with that card .

My BenQ BL3201PT does unfortunately not have a VGA input to test. The only VGA inputs I have to test are the original CRT and the input to OSSC.

maxtherabbit wrote on 2021-07-24, 14:50:

the PVGA1A is a bog standard VGA ASIC, it should not be producing bizarre non-standard text modes unless the video BIOS is programming it to do so

Do you have any secondary way of verifying what timings are coming out of the card? Scope, logic analyzer, frequency counter, OSD on the CRT, etc. ?

Thanks for prompting to do this. Gave this a look with my general multimeter that has a Hz counter, and I find some peculiar behavior.

1) If I boot the PC with no peripheral (OSSC nor original monitor) connected to the VGA at all (or with just a VGA cable connected but no peripheral attached at the other end of the VGA cable), then the system will boot with vsync=70hz (measuring between pins 10-14 of VGA). If I connect OSSC to the PC via VGA _after_ having turned the PC on, it will properly output an image with 70hz to BenQ HDMI display.

2) if I boot the PC with a peripheral connected to the VGA port, then the PC will boot to output vsync=87hz from the VGA port. If I disconnect the cable while the PC is running, and double check with the multimeter, it confirms a vsync of 87hz. (disconnecting and reconnecting does not revert/change the vsync rate)

So there is definitely some special BIOS logic going on here.

Since this logic is done at boot, the original monitor can be tricked to take in a 70hz signal by disconnecting the VGA cable, and then only connecting it after the PC has booted. Trying that out, the original monitor is able to display this 70hz signal as well, but the produced geometry is slightly different from the 87hz signal. Attached two screenshots that show the slight difference. (look for the horizontal spacing between the image left frame, and the leftmost characters on the display, also slight difference on top side)

Reply 7 of 22, by darry

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Sorry for suggesting a direct VGA connection to the monitor. The manual here https://www.benq.com/en-ap/support/downloads- … 1pt/manual.html implies a D-SUB VGA is present . I imagine that you have a variant without it .

On a card that old, I would imagine there is no DDC functionality . That being said, trying a different VGA cable and/or modifying a cable to remove all pins except the essential ones (RGB Hsync and Vsync) would be worth a try .

Reply 8 of 22, by maxtherabbit

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It's not DDC, it's the ID pin scheme that came before. Easy mode to solve this problem would be a VGA to BNC breakout and vice versa connected together

Reply 9 of 22, by clb

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darry wrote on 2021-07-24, 16:29:

On a card that old, I would imagine there is no DDC functionality . That being said, trying a different VGA cable and/or modifying a cable to remove all pins except the essential ones (RGB Hsync and Vsync) would be worth a try .

The original VGA monitor does omit pin 9 (https://en.wikipedia.org/wiki/VGA_connector , "KEY/PWR. +5 V DC (powers EDID EEPROM chip on some monitors), formerly key"), but the 87hz mode does kick in even with that pin omitted, so it is not at least triggered by that pin.

I wonder which pins I would need at minimum for a VGA cable? I could try removing pins from one VGA cable to see if any of those cause it. From the pinout:

Pin 1 RED Red video
Pin 2 GREEN Green video
Pin 3 BLUE Blue video
Pin 4 ID2/RES Reserved since E-DDC, formerly monitor id. bit 2 (*)
Pin 5 GND Ground (HSync)
Pin 6 RED_RTN Red return
Pin 7 GREEN_RTN Green return
Pin 8 BLUE_RTN Blue return
Pin 9 KEY/PWR +5 V DC (powers EDID EEPROM chip on some monitors), formerly key (*)
Pin 10 GND Ground (VSync, DDC)
Pin 11 ID0/RES Reserved since E-DDC, formerly monitor id. bit 0 (*)
Pin 12 ID1/SDA I²C data since DDC2, formerly monitor id. bit 1 (*)
Pin 13 HSync Horizontal sync
Pin 14 VSync Vertical sync
Pin 15 ID3/SCL I²C clock since DDC2, formerly monitor id. bit 3 (*)

Could I try removing pins that I marked with stars: 4, 9, 11, 12, 15? The DDC mechanism looks like originated with VESA in 1996, but not sure if either side will do anything with the monitor ID bits.

Reply 10 of 22, by clb

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clb wrote on 2021-07-24, 16:41:

Could I try removing pins that I marked with stars: 4, 9, 11, 12, 15? The DDC mechanism looks like originated with VESA in 1996, but not sure if either side will do anything with the monitor ID bits.

Actually, further testing it looks like this won't work. If I do the "don't-connect-a-vga-cable-at-boot" trick, then the adapter goes in some kind of grayscale mode: BIOS shows black and white colors, but also games, e.g. Commander Keen 1 are shown in grayscale instead. (It is not just 1-bit monochrome it looks like, but there are some shades of gray)

Reply 11 of 22, by mkarcher

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It seems as if the BIOS tries to detect (likely using some or all of the monitor ID pins 4, 11, 12, 15) whether a high-refresh capable monitor is connected and switches to the 87Hz mode in that case. I never heard of that mode being used in practice till now, but the timings look like every multi-sync monitor that can display both 1024x786 @ 87i and 1024x786 @ 60 (non-interlaced) should easily be able to synchronize to the high-refresh text mode, too.

Reply 12 of 22, by mkarcher

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clb wrote on 2021-07-24, 17:09:
clb wrote on 2021-07-24, 16:41:

Could I try removing pins that I marked with stars: 4, 9, 11, 12, 15? The DDC mechanism looks like originated with VESA in 1996, but not sure if either side will do anything with the monitor ID bits.

Actually, further testing it looks like this won't work. If I do the "don't-connect-a-vga-cable-at-boot" trick, then the adapter goes in some kind of grayscale mode: BIOS shows black and white colors, but also games, e.g. Commander Keen 1 are shown in grayscale instead. (It is not just 1-bit monochrome it looks like, but there are some shades of gray)

The grayscale mode is a good indicator that the VGA BIOS uses the monitor ID pins in some way. A color monitor is supposed to ground pin 12. If the BIOS doesn't detect pin 12 grounded, it might assume a monochrome monitor and set the corresponding bits in the BIOS data area (40:89, Bits 1 and 2), which seems to be read by Commander Keen.

Reply 13 of 22, by maxtherabbit

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Just pull pin 12 down with a bodge wire on the mobo then

Reply 14 of 22, by clb

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I measure no resistance between pins 10 and 12, so I connected them with a 10kOhm resistor in between.

Doing that, and booting with nothing connected to the VGA port except the pins 10-12 via the resistor, the system boots with a yet third refresh rate:

hsync=31.46kHz,
vsync=58.92hz,
ossc detected mode=534-p
H. samplerate: 800, H. s.rate frac: .00, H. synclen: 96, H.backporch: 48, H. active: 640, V.synclen: 2, V. backporch: 33, V. active: 480, Sampling phase: 180 deg

Anyhow, I think this is derailing from the original conversation. I don't think I want to go down this route.

It was suspected that the system would not actually be generating a 87Hz vsync, but it has now been investigated that it actually does.

I would like to now focus back on the original conversation at hand:

1) does anyone know of VGA->HDMI converters they have had good success with DOS? or
2) any good LCDs with higher refresh rate support? or as a fallback,
3) any good CRTs with higher refresh rate support?

Reply 15 of 22, by darry

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clb wrote on 2021-07-25, 06:45:
I measure no resistance between pins 10 and 12, so I connected them with a 10kOhm resistor in between. […]
Show full quote

I measure no resistance between pins 10 and 12, so I connected them with a 10kOhm resistor in between.

Doing that, and booting with nothing connected to the VGA port except the pins 10-12 via the resistor, the system boots with a yet third refresh rate:

hsync=31.46kHz,
vsync=58.92hz,
ossc detected mode=534-p
H. samplerate: 800, H. s.rate frac: .00, H. synclen: 96, H.backporch: 48, H. active: 640, V.synclen: 2, V. backporch: 33, V. active: 480, Sampling phase: 180 deg

Anyhow, I think this is derailing from the original conversation. I don't think I want to go down this route.

It was suspected that the system would not actually be generating a 87Hz vsync, but it has now been investigated that it actually does.

I would like to now focus back on the original conversation at hand:

1) does anyone know of VGA->HDMI converters they have had good success with DOS? or
2) any good LCDs with higher refresh rate support? or as a fallback,
3) any good CRTs with higher refresh rate support?

AFAIU, the Paradise VGA card you have behaves in a way the is not representative of a normally working VGA card under DOS . Respectfully, I believe it would be more productive to try to address/fix the issue with your Paradise card than to try to seek out exotic and expensive hardware to try to satisfy that specific card's non standard needs (could it be defective?) . There exists a utility that should be able set the card to color mode after boot, if I understand the included doc . See here VGA1024.EXE, Paradise video graphics switcher . If this works to force color mode after booting with monitor disconnected, this may form the beginning of a solution . EDIT : I was infer the impression that the WD90C00 an PVGA1A werr essentialltly the same or at least very similar, however, if this utility does not work, sourcing one specifically for the PVGA1A would be my next suggestion .

That being said, to try to answer point 1)
Extron RGB DVI 300 or RGB HDMI 300 . It will accept 60Hz and 70Hz (not sure about 87Hz), but always output (convert) to 60Hz. Probably the best solution for someone with a monitor that only accepts 60Hz (not your case) .

For point 2, I use a 75Hz capable Philips 252B9 (no frameskip) . See Re: Purchasing a 4:3 LCD for DOS/DOSBOX/MISTER/OSSC games? . I strongly doubt it would handle 87Hz .

Reply 16 of 22, by clb

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darry wrote on 2021-07-25, 08:14:

AFAIU, the Paradise VGA card you have behaves in a way the is not representative of a normally working VGA card under DOS .

I agree that this is not a standard VGA behavior.

darry wrote on 2021-07-25, 08:14:

Respectfully, I believe it would be more productive to try to address/fix the issue with your Paradise card than to try to seek out exotic and expensive hardware to try to satisfy that specific card's non standard needs (could it be defective?) .

I do not think there is a defect in the card. It creates a stable clock and a stable image, and shows consistent behavior across reboots. There is nothing to suggest a defect, and I have not heard of a failure mode before where a stable clock signal would get replaced with another stable clock signal that retains a perfect non-observable visual change to output image on the original monitor.

It is more likely that the manufacturer has decided to overclock the card output, since the PC was always sold with a matching monitor. This was likely done to offer reduced eye strain. Not surprised if their marketing leaflet even would have stated that. I could be wrong, but that is my impression of the scenario.

Gaming monitors with 1440p 120hz+ are the norm these days and prices are not bad at all. It could be possible that at least one of those models might support also a wider range of HDMI refresh rates even though my ASUS displays specifically don't. I don't want to rule that possibility out from my personal manufacturer sample size of one, hence making inquiries about experiences other may have had on this.

darry wrote on 2021-07-25, 08:14:
There exists a utility that should be able set the card to color mode after boot, if I understand the included doc . See here VG […]
Show full quote

There exists a utility that should be able set the card to color mode after boot, if I understand the included doc . See here VGA1024.EXE, Paradise video graphics switcher . If this works to force color mode after booting with monitor disconnected, this may form the beginning of a solution . EDIT : I was infer the impression that the WD90C00 an PVGA1A werr essentialltly the same or at least very similar, however, if this utility does not work, sourcing one specifically for the PVGA1A would be my next suggestion .

That being said, to try to answer point 1)
Extron RGB DVI 300 or RGB HDMI 300 . It will accept 60Hz and 70Hz (not sure about 87Hz), but always output (convert) to 60Hz. Probably the best solution for someone with a monitor that only accepts 60Hz (not your case) .

For point 2, I use a 75Hz capable Philips 252B9 (no frameskip) . See Re: Purchasing a 4:3 LCD for DOS/DOSBOX/MISTER/OSSC games? . I strongly doubt it would handle 87Hz .

Thanks, I'll look into this utility. Also Philips 252B9 looks interesting, good to know there are at least some monitors that can do 70Hz without frameskip.

Reply 17 of 22, by maxtherabbit

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sometimes discrete VGA adapters will have jumpers to force certain monitor detection - is it possible your motherboard has similar?

Last edited by Stiletto on 2021-07-27, 03:22. Edited 1 time in total.

Reply 18 of 22, by clb

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There are some jumpers, but unfortunatly no notes on them. I have not dared to adjust them in the chance of doing damage to the board - in the absence of documentation for the motherboard.

Reply 19 of 22, by clb

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On archive.org I found a publication on Nokia's own "Softari" magazine issue 2/1989, which announces the new MikroMikko 4 PC lineup that is in question here.

https://ia803103.us.archive.org/17/items/Soft … 2-1989_text.pdf

That issue contains a piece about display eye strain and refresh rate, and then in the publication piece, they indeed advertise the refresh rate of Nokia's monitor lineup being "up to 99 hertz in 'extended' VGA mode". Attached direct screencaps from the article in question for quick reference (in Finnish).

The PC and monitor is like shown in the advertisement photo on the left page.