Analog I/O board RGB levels

ash2fpga
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Analog I/O board RGB levels

Unread post by ash2fpga »

I randomly stumbled upon this post about RGB levels. I don't have the equipment to test this on my own mister. Could anyone shed any [more] light on this?

https://twitter.com/BartBrinkhuis/statu ... 9788459008
Today I've learned that the MiSTer IO Board outputs 1/4 less green on the VGA/RGB lines. Check for yourself. I measured my PVM on the Texio pat gen and on the MiSTer. Pretty big difference.
Edit: I just realized this should probably go in Official Addon Boards instead of Display Devices, if any mods want to move it.
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jrronimo
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Re: Analog I/O board RGB levels

Unread post by jrronimo »

I'm pretty interested in this. I've posted probably too much about issues getting some cores to sync properly, though they do sync if there's a bright enough screen. If the green is a little low, that could explain what's going on (from my very limited knowledge; I could also be totally off base.)

It's probably a non-issue and not at all related to my problems, but I can hope, hah.
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LamerDeluxe
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Re: Analog I/O board RGB levels

Unread post by LamerDeluxe »

If green levels are too low, the resulting image will have a magenta tint.
pacoarcade
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Re: Analog I/O board RGB levels

Unread post by pacoarcade »

Maybe it's due to tolerance in Analog I/O board resistors?

I use CRT with Direct video output so it should be fine.
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dshadoff
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Re: Analog I/O board RGB levels

Unread post by dshadoff »

The VGA RGB levels are actually about 10% too high - causing some displays to react badly, including:
- failure to sync
- dimming
- altering color

This has come up many times before, so it should be easy to find those other threads discussing it.
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legacypixels
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Re: Analog I/O board RGB levels

Unread post by legacypixels »

dshadoff wrote: Sat Oct 09, 2021 6:07 pm The VGA RGB levels are actually about 10% too high - causing some displays to react badly, including:
- failure to sync
- dimming
- altering color

This has come up many times before, so it should be easy to find those other threads discussing it.
It actually depends on which resistors the board builder has chosen for the R2R DAC (on 6.x boards).
You can get very close with some not-impossible-to-find values.
US based seller of MiSTer addon boards. Visit https://www.legacypixels.com/mister
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darksakul
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Re: Analog I/O board RGB levels

Unread post by darksakul »

The real problem is almost anyone can make a I/O board, and there been many variants and adjustments made.
For a while there was a inconsistency on what LEDS and Push buttons sizes are used on some MiSTer boards, and some of the Chinese made IO boards don't include all the pins for the SNAC.

It can be too easily someone use the wrong Resistors on the board.
It is my great regret that we live in an age that is proud of machines that think and suspicious of people who try to.
dshadoff
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Re: Analog I/O board RGB levels

Unread post by dshadoff »

Well, the 'official' board offers two choices for the resistor ladder, so even then I was assuming one of those two.
It is possible to get a better divider.. but then one enters the realm of 'custom', to be honest.

With all these permutations, the original poster is probably even more confused about what's going on in his setup... so realistically, this is something that he should be taking up with the board manufacturer, I think - or at least discussing based on where he obtained the board.
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legacypixels
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Re: Analog I/O board RGB levels

Unread post by legacypixels »

Indeed. I saw all kinds of crazy values on the china 5.x boards
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jrronimo
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Re: Analog I/O board RGB levels

Unread post by jrronimo »

For what it's worth, MisterAddons is saying this isn't true: Twitter link
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legacypixels
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Re: Analog I/O board RGB levels

Unread post by legacypixels »

So to be clear, there will be small level variances with the R2R resistors, there's no way it would be "1/4 off"
US based seller of MiSTer addon boards. Visit https://www.legacypixels.com/mister
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