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NTSC VIdeo Question — Parallax Forums

NTSC VIdeo Question

ke4pjwke4pjw Posts: 1,155
in General Discussion

So I am trying to upscale the video for my Color Computer 3 so it can be displayed on a VGA monitor. I have a GBS-8200 that I thought should work, however it will not properly sync. I am wondering if the HSYNC is inverted and the upscaler can't deal with that. Here is an image of the hsync line with the red line as a reference.

Any video gurus out there that might know what it should look like?

Comments

  • ke4pjwke4pjw Posts: 1,155

    OK, I think I figured it out. The RGB is composite levels and the HSYNC and VSYNC are at TTL levels. The BGS-8200 needs csync (composite sync). I think that is the issue.

  • LtechLtech Posts: 380

    Try mix them together with resistors as hv sync

  • Wuerfel_21Wuerfel_21 Posts: 5,044

    composite sync just means combined H/V sync. That's a separate issue from whether the sync is at video level or TTL level.
    The GBS board should accept TTL-level H/V sync just fine. (obviously not through the 5-pin connector though).

  • ke4pjwke4pjw Posts: 1,155

    @Wuerfel_21 so I saw where it works best with composite sync, but yes, it is supposed to do RGBHV. It will not sync to the CoCo 3. Looking at the signal above, the pulse goes high between frames. Looking at VGA, the signal goes low between frames.

    Also the CoCo appears to do inverted V-Sync as well.


    Is that what I am seeing in the documentation? If you think so, I am going to build a circuit to invert them and see if that works.

    @Ltech said:
    Try mix them together with resistors as hv sync

    Tried that. No joy.

    Luckily I have a multisync NEC LCD Monitor that the CoCo 3 works fine on. Only a handful of VGA monitors can produce an image from the signaling. (15KHz) I think it is something really silly that prevents it from working with the BGS-8200. I haven't found anyone that has been able to get it to work.

  • Wuerfel_21Wuerfel_21 Posts: 5,044

    Sync polarity shouldn't really matter on anything even slightly digital. Though idk, these GBS boards have a reputation for being bit a bit shoddy (though people do mod them for improved quality etc)

  • LtechLtech Posts: 380

    I remember some RGB signals have the sync in the Green signal ?

    My previous guess is confirmed by: but inverted
    https://www.retrorgb.com/building-a-passive-sync-combiner.html

  • DigitalBobDigitalBob Posts: 1,513

    Those RGB/CGA/EGA to VGA converter boards work well from Amazon, about $20

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