mini-DVI to DVI adapters and analog signals

Discussion in 'MacBook Pro' started by tuc, Dec 1, 2007.

  1. tuc macrumors 6502

    Aug 25, 2003
    It seems obvious that it would be possible to build a mini-DVI to DVI-I adapter that carries both digital and analog signals. After all, Apple sells adapters that convert from mini-DVI to both DVI and VGA, so both analog and digital signals must be available in the mini-DVI port.

    [Apple says of mini-DVI, "The computer detects which adapter is present by reading its EDID (Extended Display Identification Data) via DDC. The EDID for video is in the adapter; the EDID for VGA and DVI are in the display." But I think we can presume (can we?) that for both DVI and VGA that the DDC/EDID conversation between the mini-DVI port and the monitor is passed straight through the adapter unadulterated. It's only the adapter that provides S-video and composite video ports that is playing DDC/EDID tricks.]

    So the only reason not to pass through the analog signals is to save a few conductors in the cable. Yet it seems both games in town have in fact done this.

    It's obvious Apple does this, since the female DVI connector on their adapter lacks sockets for the analog pins. (See this image to confirm that it's a DVI-D socket connector that won't physically accept the analog pins (above and below the blade pin) of common DVI-to-VGA cables such as this one.

    The only other manufacturer of mini-DVI to DVI adapters I can find is Dynex. Dynex's mini-DVI to DVI cable has a female DVI-I connector, so analog cables will physically fit, but this thread confirms that the analog signals aren't passed. The DDC/EDID data gets through, but either there aren't conductors for the analog signals or possibly the RAMDAC that would be generating the analog signals is somehow getting shut down.

    It would be nice to be able to carry around a single mini-DVI adapter that could provide both digital and analog signals. Comments?
  2. nuovo macrumors newbie

    Dec 15, 2007
    Using Cinema Display multiple video sources

    Does this mean that with the DVI adapter I can attach my (future) Cinema Display to accept a video feed from the computer or other VGA source as well as from DVD or a live feed? Can the screen itself manage the switching or do I need an external switch too?

    I have a large plasma in my office which I use occasionally as a computer monitor (VGA input) but more frequently for live feed from a video camera. I would like to drive a Cinema Display alongside th plasma as a second sreen.
    Thanks for help.
  3. DeathscytheSeph macrumors newbie

    Jul 9, 2007
    Do you mean that if I have Macbook I can't use mini-DVI to DVI adapter and then use DVI to VGA adapter?
  4. tuc thread starter macrumors 6502

    Aug 25, 2003
    Yes, that is correct. It sounded crazy to me, too.

    If you use Apple's adapter, your DVI-to-VGA adapter won't even physically fit onto the DVI-end of the miniDVI-to-DVI adapter (or, presumably, the microDVI-to-DVI adapter used by the MacBook Air).

    If you use Dynex's adapter it will physically fit but it still won't work (as confirmed here).

    [PS for nuovo: I can't figure out what you are trying to ask.]
  5. rcpmac macrumors newbie

    Jun 24, 2002

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