Mode 13h / 400p, 70 Hz compatibility

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    Putting Mode 13h stuff (400p, 70 Hz) from my DOS gaming PC through the OSSC results in “Out of range”-messages / black screens on all monitors I tried it on (all compatible with Mode 13h by themselves, albeit incompetent when it comes to sampling and scaling it).

    According to the OSSC’s “Sampling opt.”-menu, it wrongly perceives Mode 13h as a 640×384 signal. Apart from that, everything seems fine; it recognizes the 70 Hz and seems to sync up nicely (see picture).

    Mode 13h

    This leads me to believe that the OSSC might just interpret Mode 13 wrongly. Is there anything that can be done about that?


    The problem might be that resulting output is 640×768 which some monitors may not support. With latest fw, 384p group horizontal is also doubled so you’ll get 1280×768 output by default. You can then use adv. timing to change it to 1280×800 which should display on most monitors.


    I changed “V. active” to 400 lines, but I still get a “No signal”-message (not “Out of Range” – don’t know where I got that from).
    Any recommendations what else I could to change? I played a bit with the other values, but so far no success…

    Edit: Decreased “V. backporch” to “1” and suddenly there’s a picture!!!! (I’m pretty much hyped now.)


    Basic sampling settings needed for Mode 13h:

    H. samplerate = 900
    V. backporch = 36
    H. active = 400

    Settings needed for makeshift aspect ratio correction (my monitor is unable to force 4:3 for the resulting 1280×800 resolution) and centering the image:

    H. backporch = 1
    H. active = 893
    H. synclen = 64

    I wish I could increase H. active even further to get an actual 4:3 image, but values above 893 yield a black picture. Well… better than nothing.



    This needs putting on the Wiki, nice work Thomago 🙂


    And another success:

    I managed to get the right sampling settings for Albion! The game runs in a funky 720×480 mode no LCD monitor I’ve ever tried it on could display without major sampling artifacts, so I find this to be quite an achievement.

    H. samplerate = 896
    V. backporch = 36
    H. backporch = 58
    H. active = 480
    H. active = 720
    H. synclen = 96

    Without the right samplerate this would look horrible!

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