OSSC + Pentium 233 MMX (VGA)

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    In case anyone wonders how the OSSC handles a retro PC with VGA only output…
    I’m in tears of joy, god bless you marqs.

    It does 640×400 (native DOS and 99.999% games) and 640×480 marvelously!!!
    640×400 runs in 384p Line2x mode but I adjusted V.Active to 480 so my screen shows it in 4:3 (1280×864),,,
    In 384p (640×400) Line2x mode the result is super sharp and smooth 70Hz, just like a quality PC CRT from back then would but on a modern LCD with HDMI.
    Yes, the screen has VGA input but the OSSC looks MUCH sharper in Line2x mode, as it would on a CRT.

    Did I say the OSSC is great already? 🙂

    Pentium 233 mmx
    doom full
    doom cu
    war2 full
    war2 cu


    Nice, I was meaning to test this more thoroughly. My TV won’t do the 70hz modes sadly (that’s to be expected).


    Although, it would be ideal to have 640×400 and 720×400 70Hz (449p) modes for PC RGBHV, because 384p is somewhat dodgy and requires extensive advanced timing tweaks, I don’t think it was meant for PC input anyway.

    Marqs you there?

    Proper 640×400 mode was added to firmware v0.81.


    Here are my advanced timing setting for 400 mode for retro PCs with OSSC firmware v0.81.
    This will result in no overscan and will show in perfect 4:3 on a PC monitor (not TV) with HDMI input.
    Note that 400p mode is 70Hz and TV don’t like that at all, but PC monitors do.

    480p in sampler: VESA 640×480@60
    Allow upsample2x: On
    384p proc: Line2x
    480p/576p proc: Line2x
    TX mode: DVI

    640×400 (PC mode)
    H. Samplerate : 700
    H. Synclength : 64
    H. Backporch : 52
    H. Active : 570
    V. Synclength : 2
    V. Backporch : 34
    V. Active : 400


    Do these settings change for higher resolutions (800 x 600 or 1024 x 768)?

    Can this work in 60Hz to use on an HDTV?


    Thank you for posting the screenshots. I see people using these old school PC’s with the OSSC, and am always interested in what is being played. Congrats, looks great!


    Can this work in 60Hz to use on an HDTV?

    The OSSC does not change refresh rate, what comes in is what comes out.
    I don’t think an HDTV will take 70Hz resolutions, so it’s mainly for modern PC monitors.
    I may be wrong so give it a try.


    So I tried your timings, but they lead to no sync at all when in text mode. Since the DOS text mode is also 400 lines, I do not see an option to use those settings, apart from loading a preset when running a game, which I find inconvenient. I use these settings in VGA text mode (720×400@70 Hz) on my 286 PC (currently with Trident 9000, but also with ET4000):

    H. samplerate 874
    H. synclen 104
    H. backporch 51
    H. active 741
    V. synclen 2
    V. backporch 32
    V. active 405

    This is obviously the same settings that is used for 320×200 games under DOS.

    Windows runs in 640×480@60 Hz using these timings:

    H. samplerate 850
    H. synclen 59
    H. backporch 56
    H. active 720
    V. synclen 2
    V. backporch 30
    V. active 480

    This leads to a good picture, although 2 lines or so at the bottom are missing. But so far I am not bothered.


    Interesting enough, using Line2X makes the 480 mode worse. See the screenshots below for an example. Both screenshots are shot with reset settings in 640×480@60 Hz:

    Default settings with passthru

    Default settings with Line2x

    And with Line2x disabled, but DTVP sampler I get this (it has some noise, black and white edges are flickery), it at least shows the whole screen:

    Default settings with DTVP sampler


    So I tried your timings, but they lead to no sync at all when in text mode.

    These settings work perfectly well on all my LCD PC monitors in text mode 720×400@70Hz as you can see on the first post of this thread, playing Doom (320×200) and Norton Commander (640×400).
    I do not see any artifacts nor the corners cut off (no overscan).
    Note that the resulting resolution will be 1152×864 (XGA+) with 384p Line2x which is in a VESA standard and works on all PC Monitors, but when not using Line2x the base 576×432 resolution is NOT part of the VESA standard.
    You can raise H.Samplerate if you have overscan and recenter with Backporch and/or Synclength.

    With 640×480@60Hz (320×240) modes, I see no artifacts nor overscan.
    Note that when using upsample2x you should always use Line2x for 480p modes since upsampling requires higher resolution to not look jaggy.
    Remember that using Line2x for 480p will output 960p, that PC monitors love, but TV’s hate.

    What PC monitor are you using?


    I wish my capture card would play nice with the 640×400 Settings you suggested. It keeps freezing. I also have to do 2x on 480p for my tv to display it correctly and I can capture that fine. Default settings for 640×400 my capture card does not have an issue with but it does crop the top.


    Using roots settings for 720×400@70 Hz which I will post below my capture device (elgato camlink is able to display the game and get sound via hdmi) my TV Samsung un32eh5300f tv detects the signal as 720x400i@70hz but wont do sound over hdmi with that resolution.
    H. samplerate 874
    H. synclen 104
    H. backporch 51
    H. active 741
    V. synclen 2
    V. backporch 32
    V. active 405

    With the default settings it detects the 384p (640×400) as 640x350i@70hz but does output the sound given to it via hdmi. With roots settings at line2x my tv will display a zoomed part of the picture and output sound but my capture card is fine with line2x.


    Ive created a file to view in DOS and adjust H.Synclenght and Phase of the most common 320×200@70 text mode (almost all games).

    Download this text file and view in DOS by using this command “edit OSSC.ADJ” or Norton Commander. OSSC.ADJ
    How it should look with proper OSSC adjustment: OSSC.ADJ Image

    In my experience I need H.Synclength of exactly 700 and Phase of 213.
    But, I can assume that different VGA cards will output either 720×400 or 640×400, so please use this file. 🙂
    PS. The code for this ASCII character is alt+176 in any dos editor.


    Hi James-F,

    Thanks for providing the settings to use for 320×200 – works really well for me.

    I think someone asked about 800×600 and 1024×768 output from a PC through the ossc. Is it possible for the OSSC to also display those resolutions? If so, what would the settings need to be? I’m still fairly new to the ossc and what settings to use etc.

    Thanks in advance!


    Should be possible to use 800×600 and 1024×768, but I would expect it to only pass-through these resolutions. (Should be technically capable of line2x for 800×600 to 1600×1200, but I’m not sure support for that is in the firmware.)

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