Laptop with reverse VGA

Jay Ashworth jra at
Tue Feb 21 14:48:21 UTC 2012

----- Original Message -----
> From: "Jake Khuon" <khuon at>

> I think the form-factour is already there. I have a Motorola Atrix
> smartphone. It's available with a laptop-dock unit. This is
> essentially a USB hub and display. The display is connected by
> outputting from the phone's HDMI port. The rest of the input/output
> device (keyboard and trackpad) are seen as USB connected devices and
> interfaced via the phone's USB port (Atrix supports USB host mode).
> Essentially, this laptop dock is what people are talking about except
> for a generic host instead of for a phone. We would want to expose the
> HDMI input generically and probably with an additional VGA input. Of
> course there are also VGA-HDMI converters. Anyone wanna ring up
> Motorola to see if they're interesting in adapting the Atrix
> laptop-dock technology? 

As someone who's done video for 20 years, I can tell you, Jake: 

It ain't that easy.

The interface on the Atrix is purpose-built, and it's almost certainly
just a DVI/HDMI digital interface to a panel that expects that.

What's necessary for a standalone KVM of the sort we're talking about
is what the video people call a "genlock" circuit -- most machines that
need this at all have analog VGA out, and you have to have a chip that
can lock up to it, and extract the video from that analog signal cleanly.

This is, to quote the Jargon file, decidedly non-trivial to do well.

That's the reason why a single port unit, not on sale, is generally around
$400.  If it was DVI/HDMI *only*, it could be substantially cheaper, but
I've never seen one that was.

- jra
Jay R. Ashworth                  Baylink                       jra at
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates         2000 Land Rover DII
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