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I'd like to know why LCD displays that have the "Auto" button need it in the first place. Are they losing sync with the signal because of some special feature or all LCD displays really suffer from this (because I don't remember having that on CRT monitors)?

Or maybe the video card's signal changes?


My desktop PC has its monitor connected via D-Sub port and sometimes the screen gets blurry and I have to press "auto".

On my netbook, there is no "auto" button and the screen doesn't seem to ever blur pixels (I assume there is some kind of special connection between motherboard and display that doesn't have this problem).

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closed as off topic by Leon Heller, Olin Lathrop, Brian Carlton, embedded.kyle, Dave Tweed Nov 16 '12 at 15:56

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2 Answers

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You will only find this feature on VGA (analog) monitors. VGA-style signals do not provide a clock signal, and so the monitor has to guess what it is, by looking at other properties of the signal. DVI signals do provide a pixel clock, and therefore there's no more guessing.

The other criterion is that a monitor can be plugged into any computer you choose. The screen on your netbook is dedicated to that computer, so the manufacturer can lock in any necessary adjustments to match it up the display without concern that it would be used anywhere else.

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The "auto" button is for dealing with analog signals. Analog signals are imperfect, as are most devices that produce them, and deciding exactly where each row starts and ends is a bit fuzzy. The auto button invokes the circuitry that tries to figure that out for a particular signal.

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So this means if I want to get rid of this problem, I should switch from D-Sub to what? –  user1306322 Nov 14 '12 at 17:45
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Switch to a digital interface: DVI, HDMI or DisplayPort –  Dave Tweed Nov 14 '12 at 17:54
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Note that DVI can pass analog (en.wikipedia.org/wiki/Digital_Visual_Interface#Analog), while HDMI and DisplayPort are digital-only interfaces. If you go to DVI to solve this issue, just be sure that you're not running analog over the DVI interface. –  HikeOnPast Nov 14 '12 at 21:38
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