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SVGA Monitor Identification Bits`

Discussion in 'Misc Electronics' started by webpa, Nov 17, 2007.

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  1. webpa

    webpa Guest

    I give up: How does a Sony (FX-140) notebook recognize the presence of
    an external (VGA/SVGA) monitor? Many Google hits on the topic provide
    monitor ID bit identifications...and variations thereon. But NONE of
    them seem to work. That is: Grounding the indicated pins, in all
    possible combinations, does not cue the computer that a monitor is
    connected. It cannot be that the FX-140 requires active communication
    with a monitor, because the computer recognizes ANY connected monitor
    (have tried 5) whether they are powered or not.

    Any hints? Diodes between pins...resistors...holy water?
  2. Bob Myers

    Bob Myers Guest

    Monitor ID pins haven't been used for a LONG time.
    The ID solution used today is a VESA standard called the
    Display Data Channel (DDC), which is based on the
    I2C electrical interface. There are two pins on the VGA
    connector which support the DDC, one clock and one
    serial data, and the PC reads a 128-byte file called the
    EDID (Extended Display Identification Data) over this
    connection. You can no doubt get more information on
    this system by Googling for "DDC" and "EDID".

    The simple presence of the monitor is also sometimes
    sensed by noting whether or not there is a load on any
    of several lines on the VGA output, including the RGB
    video pins (pins 1, 2, and 3) or the +5 VDC pin that is
    also provided under the DDC standard (pin 9).

    Bob M.
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