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ISA Super VGA Sergey’s - monochrome

dippaolo

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Hello

I made an ISA Super VGA card. PCB V1.1.

On a Commodore PC10 computer, the video is monochrome.

1. I removed FB6 and C17 - no change, monochomatic video
2. Bios 3.51 and 4.01 - no changes, monochomatic video
3. I connected the original TRIDENT VGA TVGA9000i card - no changes, the video is also monochrome
4. I connected the card in PC40 - the video is in color.

PC10 - monochrome video
PC40 - color video
 

Svenska

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Trident VGA cards have issues with modern monitors which use DDC signalling. This causes Trident cards to misdetect a monochrome VGA monitor and configure themselves into monochrome mode. In some configurations, the behaviour is very consistent, while many other configurations are fully unpredictable.

This appears to be either a chipset or video BIOS limitation, and so likely affects modern builds as well.

The proper hardware fix is to modify the VGA cable by removing the DDC pins. This prevents the Trident card from being confused by the signals. Of course, this cable will no longer support monitor auto-detection. Alternatively, the card itself can be modified instead (cutting the DDC traces).

If you do not want to modify the hardware, you can run a small program to switch back to color mode after boot. See the thread at https://forum.vcfed.org/index.php?t...at-thinks-colour-monitor-is-monochrome.79054/ for how to create this program in DOS DEBUG.
 

Timo W.

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Trident VGA cards have issues with modern monitors which use DDC signalling.
Did you actually read what his issue is? He gets color when swapping the computer but keep the VGA card and monitor.

@dippaolo: does the PC10 have a BIOS? If so, what video card has been set there? If it is set to mono in the BIOS, that's what you get.

What happens if you type "mode co80" at the DOS prompt?

Some graphics cards also rely on the 14 mhz clock crystal on the mainboard, especially cheaper ones. Not sure if that is the case here as well, but you want to check if that crystal is working on the PC10. Though it should not be used by VGA.
 

Svenska

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Did you actually read what his issue is?
Of course not. I never learned to understand squiggly.

A Trident VGA card coming up in the wrong mode is consistent with DDC issues experienced by others. Depending on the system, it can be very consistent (either color or monochrome), or it can be very unpredictable. Running the COLOR.COM program and reporting back whether it works may confirm this theory. It may also be a decent workaround.

A BIOS setting of "MONO" tells the BIOS to expect an MDA or HGC compatible card. If only a VGA card is installed, this setting will (depending on BIOS) either result in an error message or silently revert back to EGA/VGA. None of my systems revert to "monochrome VGA" mode, as that is a function of the video BIOS, not the system BIOS.

But what do I know. I'm just trying to help. Maybe I should just stop.
 

dippaolo

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I took the test again. Original ISA SUPER VGA or ISA Trident card

- Second monitor, second VGA cable - no changes, monochrome screen. COLOR.COM - screen frozen. mode co80 - screen frozen.

- I connected PC20. Same board as PC10. No changes, monochrome screen. COLOR.COM - screen frozen. mode co80 - screen frozen.

- I connected an older computer, PC10-S - it works! Color screen.

- I connected Atari PC3 - it works! Color screen.

I believe that PC10 (PC20) motherboards have a problem.
 

Svenska

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According to Wikipedia, the PC 10 and PC 10-S should be the same system, and both should be compatible with the IBM PC. If the utility works on one system, it should also work on the other.

In a dual-adapter situation, "mode co80" can appear to freeze the screen. What happens if you use "mode bw80" instead?

Does the system still respond to commands when the screen is frozen? Can you get it back by running "mode mono"?

Are there video switches on the main board, and are they set correctly?
 

dippaolo

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I wrote it bad. Sorry.

Does not work on PC10III and PC20III (I wrote PC10 and this is a mistake)

PC10-S is large, the motherboard is large. PC10III and PC20III have a smaller motherboard and have a smaller housing.

PC10-S has no integrated graphics card. PC10III and PC20III have an integrated graphics card.
 

dippaolo

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@Svenska Thank you!!!
I checked the dipswitch on the rear panel. I had it set to "MONITOR COLOR 80". I changed to COLOR 40 - monochrome screen. I changed it to "MONOCHROME" and there is color!!! WORKS!!!
Not logical... but it works...
xt.png



The manual also says "NO MONITOR" - monochrome screen.
xt2.png


Color screen only on "MONOCHROME".

Thank you all for your help :)
 

Eudimorphodon

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I checked the dipswitch on the rear panel. I had it set to "MONITOR COLOR 80". I changed to COLOR 40 - monochrome screen. I changed it to "MONOCHROME" and there is color!!! WORKS!!!
Not logical... but it works...

If the built-in video on this computer is enabled and set to either of the COLOR settings it's going to technically be interfering with the VGA card; there's going to be an I/O port overlap between the CGA CRTC registers and the equivalent parts of the VGA chip that (partially) emulate them, and it's going to map RAM into the B8000 area where the color framebuffer goes. Setting the onboard video to "Monochrome" eliminates these conflicts, because the onboard video of the machine will look like an MDA/Hercules card in terms of I/O and memory mapping. (Once upon a time having both an MDA and a color card in the same system at the same time wasn't *that* rare; the dos MODE command supports switching which head is the default for the DOS command line, and programs like Lotus 1-2-3 could do things like display a spreadsheet and a graph at the same time. Support for this continued into the VGA era, even early Windows, with an MDA second head used to display a debugger when testing software on the main display.)

As to why the VGA card was coming up in monochrome instead of failing entirely, well, here's my half-***ed theory: Even though it was rare and kind of pointless *EGA*, of which VGA is a superset, technically supported being configured to drive a monochrome monitor and coexisting with a CGA card. Maybe what's going on here is the Trident BIOS is detecting the presence of the CGA hardware and configuring itself to a monochrome-only mode to avoid the hardware conflict? It might be possible to reproduce this by jamming the card into a machine that also has a CGA card in it. (Also leaving the motherboard switches, etc, for CGA.)

What's sort of goofy here is I would have expected that the "NO MONITOR" setting would be a "disable" setting which would prevent the onboard video hardware from showing up as *either* MDA or CGA. Maybe Commodore screwed up somehow and the card is still "detectable" as a CGA card even when it's set to this position. Which is why you have to use the "MONO" setting.
 
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Svenska

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I checked the dipswitch on the rear panel. I had it set to "MONITOR COLOR 80". I changed to COLOR 40 - monochrome screen. I changed it to "MONOCHROME" and there is color!!! WORKS!!!
Not logical... but it works...
This switch is for the mainboard video system (which the PC 10 does not have), which can be switched in two modes. But you are trying to use a separate VGA card.

Setting it to "COLOR 80" or "COLOR 40" turns it into a CGA-type card which conflicts with a VGA card.
Setting it to "MONOCHROME" turns it into a Hercules-type card which works together with a VGA card.
Setting it to "NO MONITOR" should disable the internal video, but that obviously does not work for you.

In any case, the DDC problem I mentioned in the beginning is still valid. If you use a modern monitor with a Trident card, there is a chance of the display coming up in monochrome. In that case, COLOR.COM will fix it after boot (as it did on your PC-S).
 
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