What is DVI (Digital Visual Interface)?

DVI (Digital Visual Interface) is a 24 or 29-terminal semi-rectangular connector that is responsible for transmitting graphic signals from a computer to a screen and displaying them to the user.

What is DVI Port?

Allows data to be sent between the computer and an external device (peripheral). These standard VGA connectors compete with HDMI connectors and S-video connectors.

Specifications

It is a semi-rectangular connector designed by the DDWG (Digital Display Working Group). It is designed to maximize the visual quality of flat-screen video devices. It is Plug and Play, meaning that when you connect the device to the computer, it works automatically without installing drivers.

They use the PanelLink data format called TMDS (Transition Minimized Differential Signaling) or signaling with minimized differential transition, which does not use any compression.

The port is responsible for sending signals from the computer to the display. It is usually found on graphics accelerator cards and video capture cards.

DVI Port Specifications

The data format is based on the PanelLink serial format developed by semiconductor manufacturer Silicon Image Inc.

A DVI connection consists of four twisted-pair cables, one for each primary color (red, green, and blue) and one for the clock. The signal timing is almost the same as that of an analog video signal.

The image is transmitted line by line, with blanking intervals between each line and between each frame. No compression or packet transmission is used, and it does not support transmission only in the changing areas of the image. This means that the entire screen is continuously broadcast.

The maximum resolution possible with a single DVI connection (or Single Link) at 60 Hz is 2.6 megapixels. Therefore, the connector supports a second connection (Dual-Link) with another set of twisted pairs for red, green, and blue. When more bandwidth is needed than a single connection allows, the second link becomes active, and both can emit alternate pixels.

The DVI standard specifies a maximum limit of 165 MHz for single links, so display modes that require lower frequencies should use single link mode, and modes that require more should set dual link mode.

When two links are used, each can exceed 165 MHz. The second link can also be used when more than 24 bits per pixel are required, in which case it transmits the least significant bits.

Like modern analog VGA connectors, the DVI connector has pins for the display data channel, version 2 (DDC 2), which allows the graphics adapter to read EDID (Extended Display Identification Data).

Overview

The above standards, such as VGA, are analog and designed for CRT (cathode ray tube or cathode tube) devices. The source varies the output brightness with each line it emits to represent the desired brightness.

On a CRT display, this is used to assign the appropriate intensity to the beam as it moves across the screen. This beam is not present on digital displays; instead, it is an array of pixels, each of which must be assigned a brightness value. The decoder does this by taking samples of the input voltage at regular intervals.

When the source is also digital (like a computer), this can distort if the samples are not centered at each pixel. In general, the degree of noise between adjacent pixels is high.

DVI takes a different approach. The brightness of the pixels is transmitted as a list of binary numbers. When the display is set to its native resolution, it reads each number and applies that brightness to the appropriate pixel.

In this way, each pixel in the source’s output buffer corresponds directly to a pixel on the screen. In contrast, with an analog signal, the appearance of each pixel can be affected by its adjacent pixels, as well as by electrical noise and other forms of analog distortion.

Monitors

The IBM T221 monitor was released in early 2003 and offers four single-link DVI connectors and a resolution of 3820×2400, or approximately 9.2 million pixels. The refresh rate connected to a single-link graphics card is only 13Hz. By connecting all four connectors to graphics cards, you can achieve 41Hz.

Some models can be connected to a dual-link graphics card, which gives a frequency of 24 Hz. However, this is achieved by using an external splitter box that converts the dual-link signal into two single-link signals for the monitor.

The Apple Computer 30-inch Cinema HD Display was released in mid-2004 and was one of the first displays on the market to use a dual-link connection. Its native resolution is 2560×1600, approximately 4.1 million pixels.

Digital Features

• Minimum clock frequency: 21 Hz Maximum clock frequency for a single connection: 165 MHz
• Maximum Clock Speed ​​for Dual Connection – Cable Only Limited
• Pixel per clock cycle: (single link) or 2 (double link)
• Number of bits per pixel: 24
• Display modes (single connection):
  • HDTV (1920×1080) at 60 Hz with 5% LCD erase (131 MHz)
  • 1920×1200 at 60 Hz (154 Mhz)
  • UXGA (1600×1200) at 60 Hz with GTF erase (161 MHz)
  • SXGA (1280×1024) at 85 Hz with GTF erase (159 MHz)

• Display modes (dual connection):
  • QXGA (2048×1536) at 75 Hz with GTF erase (2×170 MHz)
  • HDTV (1920×1080) at 85 Hz with GTF erase (2×126 MHz)
  • 2560×1600 (on 30-inch LCD screens)

GTF (Generalized Timing Formula) is a VESA standard.

DVI Advantages

Not so long ago, the DVI port started to be used for graphics card connections and quickly became established to the point where not only the vast majority of graphics cards have this type of connection but also the VGA connection. But now there are more and more high-end graphics cards.

Given this, it is logical to ask what the differences are between these two ports and which one is better.

For this, you will see what types of ports are being talked about, how they work, and what kinds of screens (monitors) are used.

VGA Connector

The VGA connector is the connector that is typically used to connect the output of our graphics card to the monitor.

Although they are known as VGA, current connectors do not really work under the VGA standard, which allows the display of a maximum of 256 colors from a color palette of 262,144 with a maximum resolution of 720×480 and a maximum refresh rate of 70Hz but SVGA allows much higher resolutions and color palettes than we are used to.

These two systems use the same type of connector called 15-pin D-sub VGA.

However, this type of connector, which works well for CRT-type monitors, cannot provide sufficient image quality for TFT monitors or other similar types. This is because, regardless of the kind of graphics card, it makes the connection to the monitor in an analog way. A simple voltage defines color depth. Therefore, in theory, there is almost no limit to the number of colors that an SVGA or VGA monitor (CRT or Cathode Ray Tube type) can display.

The brightness of each color is determined by a change in the intensity of the beam as it moves along the corresponding line.

However, in the case of a TFT monitor, which, as we know, is the most used today, this does not happen in the same way. And this is so because this type of display does not use this cathode ray system. Instead, it works with a matrix of pixels, and it is necessary to assign a brightness value to each of them.

This is done using a decoder that receives voltage inputs at regular intervals. In order to avoid noise and color distortions, this system creates a problem when both the emitting source and the receiving source are digital. This requires taking the sample precisely in the center of the pixel. This causes, among other things, the tone and brightness of a pixel to be affected by those of the surrounding pixels.

DVI Connector

This is done in the DVI format since it is a digital format. So, the brightness of each pixel is transmitted using binary code.

This means that when a TFT screen works with a DVI connection and in its native resolution, each output pixel corresponds to the pixel on the screen, and the pixels have the exact color, quality, and brightness. For this to happen, both elements must have digital connections (DVI or HDMI).

However, not all monitors have this type of connection, so there are DVI-VGA adapters on the market. As we said, most graphics cards adopt this type of connection. And in many cases, they even eliminate VGA connections.

This is because DVI connectors can transmit both analog and digital signals in one of the models used by graphics cards (DVI-I).

Connector Types

There are several types of connectors, depending on the types of signals they can transmit:

1. DVI-D broadcasts only digitally.
2. DVI-A transmits a single analog.
3. DVI-I transmits both digital and analog signals.

In contrast, DVI-D and DVI-I types can be dual (DL or Dual-Link). That is, it can support two links.

The Battle Between DVI and HDMI

If the battle between HD-DVD and Blu-ray is challenging, the struggle between DVI and HDMI has been quieter, although it seems to lean towards the latter technology. But it also appears to have a clear winner: HDMI.

HDMI has surpassed DVI, especially in the field of consumer devices such as televisions, consoles, cameras, and both video and photo. It includes audio in the same cable, and its connectors are of the same style, similar to USB, smaller and more manageable.

In computers, where DVI is mainly applied for connecting to monitors, it is likely to replace DisplayPort, which includes some of the innovations that HDMI already has.