Re: About Apples DVI output on a MacBook Pro.

On Sep 12, 11:13 pm, demp...@xxxxxxxxxxxxx (David Empson) wrote:
SpreadTooThin <bjobrie...@xxxxxxxxx> wrote:
The DVI connector on a MacBook Pro is a Dual Analog / Digital output.
Why is it dual? Can it drive two displays?

The DVI connector supports either a digital or an analog display. This
is to give you more choices for supported monitors. It can't support
both digital and analog monitors connected at the same time.

I know.

The term "Dual" should be used with caution when referring to a DVI - it
might be confused with "Dual Link", which means the connector is able to
supply twice as much data to drive a larger display. (This is the
question I answered in the previous thread.)


I see two sets of data links.


I'm not talking about the F7 Mirroring function...

That sets the external display to be either a mirror or independent of
the built-in display.

I said I'm not talking about it... :)

I'm talking about the fact that there connector looks like its capable
of driving two DVI displays.

It isn't.

There we go.


If in fact it can only drive one display which channel of the DVI
output is actually being driven?

A dual-link DVI-I connector has two digital video "links" as well as
analog.


Right. Which is why I wondered if it might drive two digital
channels.


For high end and most recent Macs with a DVI connector (including the
MacBook Pro), the dual-link functionality is supported. (Some older
models have the same connector, but only support single-link displays.)

There are three possible modes of operation for the DVI port:

1. If you connect an analog monitor, the analog outputs are used.

2. If you connect a low to medium resolution digital monitor, the first
digital link is used.

3. If you connect a high resolution digital monitor (e.g. Apple's 30"
Cinema Display), both digital links are used.

I see.

Or is it smart enough to know which one is connected and drive it?

It uses the data supplied by the monitor on the DDC input to identify
what type of monitor is connected, whether it is digital or analog, and
what video display modes it supports. It then generates the video signal
on the appropriate set of pins (analog only plus sync signals, or
digital only using the "link 1" set of pins, or digital only using both
the "link 1" and "link 2" set of pins).

I see.

A single monitor can identify itself as supporting both digital and
analog, in which case the computer will pick one. (The Wikipedia article
you referenced implies that the analog mode will take priority.)

You can't connect two monitors directly to a DVI port, because there is
only one input signal which lets the computer identify a connected
monitor.

Ok.

The only way to connect two monitors to a DVI port would be to use
external hardware which had three connectors on it: one goes to the
computer's DVI port, and it has two female DVI ports (or a mixture of
DVI and VGA) for connecting two monitors.

Not what I'm trying to do.
I thought maybe I had a cable issue and that that was why my monitor
was not working with my laptop.. I thought maybe there was a specific
cable that used data link 1 and another that used data link 2.
Sorry I worked with RS232 cables and there were allways these kinds of
issues.

Such a device would probably require manual configuration to set the
available video modes, or would have some restrictions about what
monitors can be connected to it. In principle, it could use the
identification data from the two monitors to determine the range of
supportable display modes, then tell the computer about a set of
combined modes that are compatible with both monitors.

In this sort of arrangement, the computer would still think it had one
monitor connected externally (e.g. the two external monitors would look
like one display in System Preferences > Displays > Arrange), so the
interface box would have to control how the two monitors were arranged
relative to each other, and you could only get a rectangular display
spread across the two monitors (as far as the computer is concerned).

There would also be a limit on the maximum resolution available in such
a configuration, which would depend on the capabilities of the
computer's video card.

I have no idea if any such device exists.

Not my goal.


--
David Empson
demp...@xxxxxxxxxxxxx


.

Relevant Pages

  • Re: About Apples DVI output on a MacBook Pro.
    ... The DVI connector supports either a digital or an analog display. ... both digital and analog monitors connected at the same time. ... You can't connect two monitors directly to a DVI port, ...
    (comp.sys.mac.hardware.video)
  • Re: DVI-I vs DVI-D Cable Connection?
    ... the digital outputs to the display, but very few displays even attempt ... to take their analog input from the DVI ... if they have both an analog and a DVI ... connector, they have two separate connectors, a DVI connector (DVI-D, ...
    (microsoft.public.windows.mediacenter)
  • Re: VGA vs DVI connection to monitor
    ... Well there are some "analog only monitors" which do have DVI ... interface was designed they made it backwards compatible ... The had to have a DVI connector. ...
    (rec.photo.digital)
  • Re: VGA vs DVI connection to monitor
    ... It is not correct to say "analog only monitors never had DVI ... Get it through your head that the connector does not ... define the interface. ...
    (rec.photo.digital)
  • Re: Best Buy Extended Warranty
    ... One set is the "pure digital" signals, which are exactly the same as those present on a DVI-D connector. ... They may be analog and digital representations of the same display image, but they may also be completely different and independent, even having different resolutions, as in a video board that supports dual-monitor configurations. ... I am not aware of ANY analog monitors with DVI connectors, ...
    (comp.sys.laptops)