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Thread: C64 white line down left edge of image

  1. #1

    Default C64 white line down left edge of image

    This is just me being idly curious, but why does the VICII chip produce a white line down the left edge of each frame?

    I don't have an LCD to demonstrate, but you can see it on my scope. It's the short spike after the colourburst. It's not visible on a CRT's normal scan as it's outside the safe area.

    Commodore_64_PAL_horizontal_sync_and_colourburst.jpg

  2. #2
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    isn't it the horizontal blanking interval between the lines?

  3. #3

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    Quote Originally Posted by PET 2001-8 BS guy View Post
    This is just me being idly curious, but why does the VICII chip produce a white line down the left edge of each frame?

    I don't have an LCD to demonstrate, but you can see it on my scope. It's the short spike after the colourburst. It's not visible on a CRT's normal scan as it's outside the safe area.

    Commodore_64_PAL_horizontal_sync_and_colourburst.jpg

    funny, you're right. I've just powered the first random C64 I could reach at home and it indeed has that spike after the color burst.
    I think it's too early to be visible anyway.
    I have no idea why VIC-II does that, might be interesting to know.

    Frank
    Last edited by iz8dwf; May 14th, 2020 at 11:18 AM. Reason: typo

  4. #4

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    By the way, that spike is present in the luma signal, so it gets mixed into the composite signal.

  5. #5

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    That is an interesting glitch as a result of some timing anomaly, probably the designers knew about the defect and just decided to leave it as mostly it would be hiding inside the H blanking time and many VDU's have horizontal blanking applied(not all), so the CRT beam is extinguished during H retrace, as well as the usual vertical retrace blanking. Still many computer VDU's, as opposed to TV's have a somewhat under-scanned raster and without effective H blanking you would see that as a visible line. It would probably drive me nuts and I'd make a circuit to gate it out, or make an H blanking mod to the monitor so I couldn't see it....EDIT: looking at the spike though, it might be just on the end of H blanking time so it still might be seen on a VDU with H blanking.
    Last edited by Hugo Holden; May 14th, 2020 at 03:27 PM.

  6. #6

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    Quote Originally Posted by giobbi View Post
    isn't it the horizontal blanking interval between the lines?
    It's right on the very edge. Here's a slightly different image with the C64 boot screen visible (the original image has everything on screen black, due to a few poke commands).

    96844281_10159760140318275_3231482742961078272_o.jpg

    What I like about this image is you can see the phase issues that produce the banding on the screen. I might one day buy one of those lumafix solutions but mine isn't all that bad.

  7. #7
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    Quote Originally Posted by PET 2001-8 BS guy View Post
    It's right on the very edge. Here's a slightly different image with the C64 boot screen visible (the original image has everything on screen black, due to a few poke commands).

    96844281_10159760140318275_3231482742961078272_o.jpg

    What I like about this image is you can see the phase issues that produce the banding on the screen. I might one day buy one of those lumafix solutions but mine isn't all that bad.
    It is very visible on an LCD but hidden on most CRTs. You can clearly see it in this video here in Adrian Black’s video here at around the 5:50 mark.

    https://youtu.be/Qb9n6S4cKuk

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