Video Card and HDTV

I get PMs and questions about connecting a computer video card output to an HDTV quite often. It came to me that a series of threads that deal with this proceedure and the issues involved would be helpful. This thread will deal with the connecting of a computer video card with DVI outputs to an HDTV with a DVI input.

Also for you strictly technical guys out there, I do take a little potetic licence to try and simplify the subject somewhat.

Introduction
The reason many TV manufacturers include a DVI connection in addition to component video was not to allow the connection of a computer. The main reason was to allow the exchange of video information in a digital format rather than analog. The DVI interface came into being due to the LCD and plasma flat panel computer monitors and projectors, and later DLP and LCOS (D-ILA) displays and projectors. Since these are fixed pixel devices an interface that would present a digital value for each pixel rather than an analog signal level made sense.

The DVI interface answered the question of, "Why start out with a digital array of pixel values then convert them to an analog signal to send to a monitor only to have the analog signal reconverted back to digital?" With the DVI interface the possibility of the signal remaining all digital is possible.

The DVI interface was also given interaction capabilities between the video card and the monitor. This allowed the computer to inquire of the monitor what the resolution and timing that it supported and then via software in the computer set the video output accordingly. This capability is actually the essence of the DVI interface, the ability to tell the source what signals the monitor will display. The earliest DVI-I interfaces were actually just VGA analog signals with the digital link to allow the information to be exchanged between the computer and the monitor. There is a cable available to convert a DVI-I output from a video card to a VGA input on a monitor.

The DVI connection that is most desirable for fixed pixel devices is the DVI-D, dual link connection. This is the connection that most HDTV manufacturers use primararily for compatability reasons.

Adoption of DVI for HDTV Signals
Since the computer was able to ask the monitor to supply information concerning its signal capabilities, as well as other information, the consumer electronics industry saw this interface (and later the HDMI) as a possible answer to the copy protection issue that had prevented HD movies from being made available for broadcast in HDTV. The entertainment industries were concerned with copy protection and insisted on a method of preventing cloning of their movies. The HDCP protocol was developed and the DVI became the first interface to have HDPC implemented. This allowed the broadcasters to "raise the HDCP flag" that would prevent a recording device connected to the DVI output from recording by shutting off the output. As long as a monitor only device was connected the output was enabled.

Computer Output Compatability
Many people think that because there is a DVI connection on their HDTV that it should be a matter of connecting a DVI cable between the two and presto! We have computer video on our HDTV screen. Well I'm sorry to say this is not the allways the case, in fact rarely.
off another forum


There are exceptions to this, primararly plasma, LCD displays and projectors. These are generally higher cost display units that are built with the connection of a computer in mind, but most HDTVs are not built with the connection of a computer. Computer monitors today will accept a vast range of video signals. Refresh rates from 50Hz to 120Hz are typical for most computer monitors, whereas most HDTVs will only handle 59 to 61Hz refresh rates. Horizontal scan ranges are also reduced compared to a computer monitor. Here is my HDTV information returned by MonInfo, a utility that can be downloaded and run to get information from your HDTV via the DVI connection:


oh yea I hate manuals