Video Cables Question

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

Threaded View
My monitor has two different kind of ports:

The desktop PC has these ports:
* DisplayPort

Right now the monitor is connected to the PC with a VGA cable.

I've seen DisplayPort-to-DVI cables for sale, but I'm not quite sure
whether there would be any advantage in using such a cable instead of
the VGA one.

What do the experts think?

Re: Video Cables Question

tb wrote:
Quoted text here. Click to load it

DisplayPort cables exist in two types.

1) Passive (cheap)
2) Active (expensive)

The necessity of each, depends on what is at
each end of the cable. For example

    DisplayPort --> VGA   (active, expensive)

So what you want to do, is price cables, and
see if DisplayPort to DVI is a cheap cable.

Note that if it is a cheap cable, it would
have DVI-D on output. The DVI-I connector has
an analog (VGA) and a digital (DVI-D) section,
and if there is such a thing as a cheap
DisplayPort to DVI cable, it just has the
digital signals on it. Which is perfectly
fine. The only reason for my warning, is
if you attempt to combine a

    DisplayPort --> DVI-D    +    DVI to VGA dongle

there would be no signal on the VGA pins.

So in general terms, it's possible for a
DisplayPort to make digital signals without
too much fuss. But some formats, such as VGA,
an active chip inside the fat end of the cable,
does a translation for you. And that costs
money. And might even need a small power adapter
plugged into the wall.


DisplayPort to DVI will look superior at the
limits of resolution. Say, for example, the
DisplayPort does "single link DVI", which has
a 1920x1200 reduced blanking limit. Well, the
picture from that would be sharp as a tack.
Whereas, if you asked the VGA port on some
computer, to make 1920x1200, it's not going
to be nearly as nice.

At lower resolutions, you would be hard pressed
to tell the difference. At 1024x768, they would
look the same. But as the native resolution requirement
goes up (driving big-ass monitor), then the DisplayPort
to DVI digital method looks better.


OK, so let's go shopping :-)

Coboc 6 inch DisplayPort to DVI Passive Adatper   $8

    "Requires a Dual-mode DisplayPort(DP++) Source"

So the price tells you it is a passive converter.

And the technical requirement in the advertisement,
tells you what to check for on the video card end.

If the video card is DP++, then it can drive the
eight dollar adapter for you. And provide
single link DVI up to 1920x1200 @ 60Hz

So before you spend $8, start researching the
DisplayPort source characteristics (on your
video card).


Re: Video Cables Question

On 7/6/2015 at 3:16:08 PM Paul wrote:

Quoted text here. Click to load it

Thanks Paul.

The desktop is a Dell OptiPlex 9020 Mini Tower with an Intel i7-4790
processor, so the Intel HD Graphics 4600 within the i7-4790 takes care
of the video signal.  The desktop has no discrete video card.

According to this link:
he-up-to-4_00-GHz>, the graphics autput is DP (not DP++), and I was
thinking about purchasing this cable:
< .

What do you think?

Re: Video Cables Question

tb wrote:
Quoted text here. Click to load it

There is a logo apparently available, for placing next
to dual-mode DP connectors.


    Dual-mode DisplayPort (also known as DisplayPort++)
    can directly output single-link HDMI and DVI signals
    using a simple passive adapter that adjusts from the
    different connector and the lower voltages used by DisplayPort.

    When a dual-mode chipset detects that a DVI or HDMI passive
    adapter is attached, it switches to DVI/HDMI mode which uses
    the 4-lane main DisplayPort link and the AUX channel link to
    transmit three TMDS signals, a clock signal and
    Display Data Channel data/clock. Dual-mode ports are marked
    with the DP++ logo; most DisplayPort graphics cards support
    this mode.

You can see the correct logo on the back of this unrelated product.

I've been trying to find confirmation on the
site, but so far, no matching situation has come up. And Intel
has a charming FAQ page, that says whether such things are
supported, could be a "BIOS issue".

I was hoping there would be some info, either in DXDIAG
or in an Intel control panel, about the hardware, but
both are "as dumb as dirt". Nothing I could spot there
would answer the question.

That leaves talking to some tech support people (at Dell
or at the Intel community forums), or, using the "two
purchase plan". Buy the dumb cable for $8, if no output,
buy an active adapter for a lot more. Active adapters
can be $30 to $100. They can have single-link DVI
(1920x1200 @ 60HZ reduced blanking), or they can
be dual-link DVI (both sets of digital pins driven
on the DVI connector) when you want higher resolutions
(like for an Apple Cinema display).

This is an example of a premium design. It draws
power from a USB port, so no worries about power.
I could spot some other, cheaper adapters, that use
the power pin on DisplayPort, and for some reason,
the digital display is full of colored snow. So check
the reviews before buying one.

I would try a local computer store, and pick up a passive
cable there, and give it a try. That would save a
bit on shipping, as the odds of you returning the
$8 cable for a refund, you'd lose more than that
on shipping.

So if the DP++ logo is present, great, a passive cable
will help you get 1920x1080 or 1920x1200 on DVI (single-link).
If the DP++ logo is missing, try the passive cable anyway,
lose $8, then face shopping for an active adapter.


Site Timeline