Technological progress in the field of high-tech is picking up speed like a fighter-interceptor. Until recently, digital electronics was associated exclusively with bulky computers in data centers, and today cell phones, laptops and plasma displays are no longer surprising to anyone. True, the ways of improving electronic equipment are sometimes quite strange, and at the beginning of the 21st century, Hi End class audio amplifiers appear on sale, on the casings of which, like on pre-war radios, samovar radio tubes proudly line up. But this is true - toys for the rich, but in fact, after the prices for powerful microprocessors fell to the level of $ 20 apiece, the transition to digital methods for creating, processing, storing and transmitting video and audio information became inevitable. From the point of view of circuitry, digital equipment is more complicated than analog, but its functionality is much wider, and some of them are fundamentally unattainable with analog signal processing.
The transition to digital audio and video formats is due to their technical and user advantages compared to analog ones.
The technical benefits include:
From the point of view of circuitry, digital equipment is more complicated than analog, but its functionality is much wider, and some of them are fundamentally unattainable with analog signal processing.
- fundamental exclusion of signal quality loss during signal transmission, rewriting and storage;
- the possibility of accurate time synchronization of video material;
- more advanced control and signal quality control systems;
- simplification of the technology for obtaining, processing, storing and transmitting a high-quality signal;
- expansion of creative possibilities of the staff of television studios;
- the ability to encrypt video data (using cryptography).
Digital format custom properties include:
- the possibility of obtaining high-quality, devoid of interference and noise pictures with multi-channel stereo sound;
- broad service capabilities of digital equipment.
It is clear that analog interfaces are not suitable for working with a digital signal or they do not fit well, so special digital interfaces were created for it.
These include the SDI/SDTI serial digital interface used in professional and studio equipment, as well as digital video interfaces. DVI And HDMI.
The last two interfaces are discussed below. The HDMI interface is an evolution of the DVI interface, it uses the same basic technologies, which is why they are covered in the same brochure.
DVI DIGITAL VIDEO INTERFACE
The problem of deterioration of signal quality characteristics during multiple analog-to-digital and digital-to-analogue conversions was solved with the advent of the new DVI standard, which can now be confidently considered as generally accepted. The group that developed the standard - Digital Display Working Group (DDWG) - was created at the initiative of Intel, it included Compaq, Fujitsu, Hewlett-Packard, IBM, NEC and Silicon Image. The DVI specification was introduced in April 1999, and working solutions using the standard were demonstrated at the same time - Fujitsu and Phillips plasma monitors, IBM and Compaq LCD monitors, and other products.
The transition from composite and S-Video to component and RGB paths allowed a sharp increase in image quality, however, unnecessary analog-digital-analog conversions significantly worsened the picture quality
The creators of the DVI standard expected that its scope would be much wider than the digital connection of a computer with a monitor. In the late 1990s, the rapid development of video technologies continued. All-digital DLP projectors were firmly in use, and LCD and CRT monitors, if they remained analog in the principle of imaging, had digital signal processing circuits. In digital form, the image was scaled and scanned, necessary for the correct conversion of the number of lines, pixels and fields. The functions for adjusting color, brightness, contrast and other video parameters were also implemented digitally. After Fujitsu began licensing plasma technology to other manufacturers, it became clear that the introduction of another type of high-quality digital display to the market was a matter of the near future.
The introduction of high-definition television has moved into the practical plane. Screen sizes grew, their resolution increased. There was not only one - meeting the current and future needs of the digital video interface market. The transition from composite and S-Video to component and RGB paths made it possible to sharply increase the image quality, however, unnecessary analog-digital-analog conversions significantly worsened the picture quality, which was especially disappointing due to the absolute uselessness of the ADC and DAC in the path consisting from a digital source (DVD, computer), a digital display and a digital processor in between. It turned out that the ADC and DAC worked only on the "wires" between the source and the monitor.
The need to create a digital interface that meets the needs of HDTV and has a solid margin for the future has become quite obvious.
Interface DVI- Digital Visual Interface - can be called a digital RGB interface with certain tolerances. The single-channel modification of the Single Link DVI format has four data channels: three of them are designed to transmit information about the primary colors: blue, green and red, and the fourth transmits the Clock signal. This achieves a maximum data rate of 1.65 Gbps or 165 megapixels per second with 10-bit encoding (this gives an effective 8 bits of data), which corresponds to a resolution of 1600 x 1200 pixels (UXGA) at a field refresh rate of 60 Hz (or 1920 x 1080 and even 1920 x 1200). Today, this more than covers the needs of modern HDTV formats.
A modification of the Dual Link DVI interface has even more bandwidth. Here everything is the same, but in double size (except for the clock signal, which does not need to be transmitted twice). Dual Link DVI is capable of transmitting QXGA (2048 x 1536 pixels) signals at a frame rate of 60Hz.
DVI transmits resolutions up to 1600 x 1200 (UXGA) at 60 Hz (or 1920 x 1080 and even 1920 x 1200). This more than covers the needs of HDTV
Despite the obvious redundancy of Dual Link DVI in relation to modern displays, devices that support this interface are being produced (for example, large displays for workstations).
Thanks to DVI technology, it became possible to remove the analog part from video adapter cards and transfer it to the monitor, which should improve image quality much more than the elimination of interference in the video card-monitor connecting cable. Since image information is transmitted digitally from the video card to the monitor, the effect of external interference is greatly reduced.
VARIETY OF DVI
There are two more types of DVI interface: DVI-D and DVI-I, the difference between which lies in the fact that in order to ensure wider compatibility of equipment of different generations in the DVI connector, in addition to the three rows of "digital" contacts, analog ones can also be provided, to which a conventional analog RGBHV signal is supplied (the same as VGA, in Fig. 1 - pins C1 - C5). Thus, a variant of the DVI interface, including analog and digital parts, is called DVI-I (Integrated), i.e. combined. Thus, in total you can find 4 types of interface:
- DVI-I Dual Link (digital + analog, up to 2048 x 1536)
- DVI-I Single Link (digital + analog, up to 1920 x 1200)
- DVI-D Dual Link (digital, up to 2048 x 1536)
- DVI-D Single Link (digital, up to 1920 x 1200)
DVI CABLE
Single Link versions may not have pins 4, 5, 12, 13, 20, 21 on the connector. DVI-D versions may not have pins C1, C2, C3, C4, C5 on the connector.
The DVI connector pinout (for a "full" Dual Link DVI-I interface) is shown in fig. 1, and the purpose of the contacts is summarized in table 1.
Table 1. DVI-I Dual Link Connector Pinouts
| Cont. | Description | Cont. | Description |
| 1 | T.M.D.S data 2– | 16 | |
| 2 | Data T.M.D.S 2+ | 17 | T.M.D.S data 0– |
| 3 | Screen for T.M.D.S 2 and 4 data | 18 | Data T.M.D.S 0+ |
| 4 | T.M.D.S data 4–* | 19 | Screen for T.M.D.S 0 and 5 data |
| 5 | Data T.M.D.S 4+* | 20 | T.M.D.S data 5–* |
| 6 | DDC clocks | 21 | Data T.M.D.S 5+* |
| 7 | DDC Data | 22 | Screen for T.M.D.S beats |
| 8 | Analog frame sync** | 23 | T.M.D.S+ beats |
| 9 | T.M.D.S data 1– | 24 | T.M.D.S beats– |
| 10 | Data T.M.D.S 1+ | 25 | Analog channel R** |
| 11 | Screen for T.M.D.S 1 and 3 data | 26 | Analog channel G** |
| 12 | T.M.D.S data 3–* | 27 | Analog channel B** |
| 13 | Data T.M.D.S 3+* | 28 | Analog line sync** |
| 14 | Power supply +5 V | 29 | Analog ground** |
| 15 | Earth | 30 |
* only for Dual Link; ** only for DVI-I
Rice. 1. DVI-D and DVI-I connectors
INSIDE: VIDEO DATA TRANSMISSION (TMDS)
The high speed characteristics of the DVI interface are achieved through the use of a signal encoding algorithm specially developed for it, which is called Transition Minimized Differential Signaling (T.M.D.S) - differential signal transmission with minimization of level differences.
Rice. 2. TMDS link
The differential (or balanced, balanced) transmission method, when the same direct and inverted signal passes through each conductor of the twisted pair, provides effective data protection from common mode interference.
Rice. 3. Balanced communication line with a differential receiver
Rice. 4. Balanced communication line suppresses interference
On the transmit side of the DVI interface is a T.M.D.S. in which the digitized RGB signal is converted and a serial data stream is formed in each of the channels. On the receiving side, on the contrary, there is a complete restoration of digital streams on channels R, G, B, as well as the Clock signal.
The transmission format is always the same: RGB color space, color depth 24 bits (8 bits per component). For high resolutions, frame rates up to 60 Hz (progressive) are supported.
Recovery uses automatic cable loss compensation and reclocking (reclocking, jitter elimination, i.e. digital signal phase jitter).
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Rice. 5. Signal before and after recovery
Recovery is effective only if the signal degradation does not exceed a certain threshold value. In this case, the digital signal is restored almost completely, without losses and errors. However, the situation only needs to worsen a little (for example, we take a slightly longer cable) - and the signal cannot be restored, and the picture is speckled with interference, “falls apart”, or even disappears altogether. This phenomenon is called the "clipping effect" and is typical for digital signals.
Rice. 6. "Effect of the cliff"
As a result, when using cables of a reasonable length and repeaters (receiver-transmitters of a signal with its intermediate recovery), it is possible to broadcast a digital signal over practically unlimited distances - without loss!
Rice. 7. Use of repeaters
The higher the resolution of the signal (and, hence, the data transfer rate in TMDS channels), the greater the loss in the cable and (ceteris paribus) the shorter the cable can be used. The DVI standard does not specify the possible cable length and signal resolution at which such a length will work. Real quality DVI cables usually work well at lengths and resolutions no greater than those shown in the graph below (given for the Single Link version of the interface):
Rice. 8. Approvals against cable lengths
In some cases, longer cables will work, but this in each particular combination of equipment requires experimental confirmation.
To overcome cable length limitations, you can:
- purchase ultra-high quality DVI electrical cables (and prices). In some cases, manufacturers of such cables guarantee their operation with maximum resolutions up to 15 meters in length.
- use a scheme with repeaters (see Fig. 7)
- use fiber optic extenders or other special solutions. Usually it is cheaper than repeaters (with more than 2 repeaters), extension cords work at distances from tens to hundreds of meters.
Rice. 9. Integrated fiber optic cable (left, length up to 100m), transmitter and receiver for use with a separate optical cable (right, cable length up to 500m)
INSIDE: SERVICE CHANNEL (DDC)
If the DDC service channel is down, video data on the TMDS channels may be blocked
The DVI-D and DVI-I interfaces, in addition to the digital channels described above, contain another one designed to exchange information between a source equipped with a video processor (for example, a PC with a video card) and a display. Channel DDC(Display Data Channel) is designed to transfer a detailed "dossier" of the display to the processor, which, having familiarized itself with it, produces the signal that is optimal for this display with the desired resolution and screen proportions. This dossier, called EDID(Extended Display Identification Data, or detailed display identification data), is a data block with the following sections: manufacturer's brand, model identification number, serial number, release date, screen size, supported resolutions, and native screen resolution.
When starting a DVI-compatible source, the HPD (Hot Plug Detect) process is activated. The source then reads the EDID data block. If the monitor refuses to give out information about itself, the T.M.D.S channel is blocked.
When using equipment that conforms to the standard and standard cables, for a simple connection circuit (source-cable-monitor), such a circuit works fine. However, in more complex cases, the DDC channel may not work - for example, if switches, distribution amplifiers, and other elements of complex AV systems are installed between the output and the display. In this case, a problem arises: how to make the output work, for example, of a laptop video card, in the absence of a service channel.
Rice. 10. Device - EDID emulator and its application
(Click on photo to enlarge)
You can "trick" the video output using a special device. Such a device stores the EDID data block in its internal memory and issues it from there at the request of the video card. In this case, the video data passes through the device "transparently". If the emulator is previously “trained” (by reading the real EDID from the real display), the signal source will “think” that it is permanently connected to the display and output data.
Many switches and distribution amplifiers for DVI and HDMI signals already have such emulators built in, which makes the installer's job easier. Note that the presence of an emulator in no way ensures the operation of the HDCP video data encryption system, for which the presence of a “live” DDC channel is mandatory.
INSIDE: HDCP DATA ENCRYPTION
Intel's HDCP (Highbandwidth Digital Content Protection) cryptographic system is a method for protecting high-resolution digital content. It provides the ability to set different levels of protection depending on the specific case, due to which it does not limit the freedom of handling video data within the framework approved by the current legislation. For example, HDCP does not provide copy protection and does not artificially degrade the quality of copies. The following actions fall under a strict ban: copying programs with the protection removed, receiving an unprotected high-resolution digital stream. Repeaters and signal splitters are allowed, but they must "exchange passwords" with each other and obtain mutual approval, which is only possible if all devices are HDCP compliant.
A special mark is recorded on the Blu-Ray disc or in the DVB stream, in the presence of which the player or receiver must enable data encryption on its digital output
Note that HDCP is not related, for example, to encryption of data on a Blu-Ray disc or a stream in a DVB receiver. These are different technologies. On the disk itself or in the DVB stream, a special label is simply recorded, in the presence of which the device (player or receiver) must enable data encryption on its digital output.
The HDCP system can work with both DVI and HDMI interfaces. True, for (mostly) computer DVI, HDCP is rarely used, while for consumer HDMI, HDCP encoding is used everywhere (and for most video programs it is mandatory).
HDCP protects the rights of the consumer by shielding him from the flow of low-grade
video production
It should be especially noted that HDCP works not only for the rights holders of film materials, but also protects the rights of the consumer, protecting him from the stream of low-quality video products (for example, received via the Internet), the quality of which is incompatible with modern high-definition television formats.
HDCP works according to a complex scheme, which primarily provides for the presence of its own "secret" code combinations in each DVI / HDMI transmitter and receiver. In a single system, up to 127 pairs of transmitters and receivers and up to 7 levels of branching (or relaying) are allowed. In order for the DVI/HDMI link to become active, each pair of transmitters and receivers must successfully pass the mutual authentication process. For this task, the same DDC service channel is used.
When HDCP is enabled, the analog outputs can produce a high-resolution picture, a low-resolution picture, or no picture at all - at the discretion of the manufacturer
The first stage of the authentication process is the exchange of code combinations that are "hardwired" into the hardware chips and are not available to the user. Code combinations must have plausibility, for the verification of which the mathematical sum R0 is calculated. The transmitter generates a pseudo-random sequence AN, which, together with the so-called. a "code selection vector" (KSV) is sent to the receiver. Similarly, a similar message is sent from the receiver to the transmitter. In the case of a positive result of the KSV check (in their structure, among other things, 20 zeros and 20 ones must be present), code generators are launched on both sides, generating 24-bit encryption codes corresponding to certain values of the "secret" parameter Ks. The values of R0 and Ks synthesized in the transmitter and receiver are compared.
KSV values are individual for each individual device. There is also a "black list" of hacked codes, which is stored in the device's memory and is updated when playing new BluRay releases (one of the ways). If the individual data of a specific device matches the data from this list, the initialization process is immediately blocked. Thus, a DVD/BluRay player once noticed in an attempt to circumvent prohibitions will become persona non grata in any system, provided that someone notices this attempt and informs where it should be.
The whole process of "starting" the operation of the DVI / HDMI interface (reading EDID, setting the output) and the HDCP system (authentication) can take up to several seconds. At this time, there is no image on the display.
When a HDCP-encoded video stream is on the digital output of a player or satellite receiver, its analog outputs can produce a high-resolution picture, or a low-resolution picture, or no picture at all - at the discretion of the device manufacturer. Unfortunately, it is extremely rare to find a description of such behavior in the documentation.
The conceptual complexity of the entire system (DVI/HDMI, DDC/EDID, HDCP) turns out to be orders of magnitude higher than that of all previously used analog interfaces. Although in mass production this practically does not lead to an increase in the cost of equipment (and theoretically even should make it cheaper), the problems of compatibility and even simple performance of equipment, especially from different manufacturers, are now extremely relevant. Features of hardware firmware and errors in the implementation of interfaces can negate all the advantages of the most expensive and advanced modern technology.
Before purchasing a set of equipment with a DVI / HDMI interface and HDCP support, be sure to turn it on and check it in all modes, including when playing content with HDCP protection enabled
Before purchasing equipment with DVI/HDMI interface and HDCP support, be sure to turn it on (the whole complex - signal sources, intermediate switches, distributors, AV receivers, displays and all connecting cables) and check it in all modes, including when playing content with HDCP protection enabled.
THE FUTURE OF DVI AND HDMI
According to Intel's optimistic forecasts, the DVI and HDMI standard will be relevant for at least the next ten years.
The crowding out of old interfaces is gaining momentum. In the not too distant future, things will most likely come to the withering away of the analog part of the video equipment. For the HDMI interface, which is replacing DVI, this has already happened (there is no analog part).
HDMI INTERFACE
An evolution of the DVI interface is the High Definition Multimedia Interface (HDMI). The HDMI video part, as well as the DDC service channel, are fully compatible with DVI, but it looks completely different, because another connector is used. HDMI is a more advanced interface than DVI, primarily due to the ability to transmit multi-channel audio. Additionally, HDMI is equipped with a CEC control interface (it is not in DVI).
HDMI is a more advanced interface than DVI, primarily due to the ability to transmit multi-channel audio
Just like DVI, the HDMI interface can be single-channel (Single Link) and dual-channel (Dual Link) (different connectors are used for these versions). The TMDS links and the DDC service channel work exactly the same as in DVI.
The bandwidth of HDMI (like DVI) reaches 5 Gb / s. This is sufficient for 1080p video and two channels of uncompressed digital audio in PCM up to 48 kHz, or 5.1 channels in Dolby Digital or DTS. Audio is transmitted mixed with video, the same TMDS lines are used (there are no additional conductors for audio in the cable).
Rice. 11. Comparison of HDMI and DVI cable plugs (right)
The HDMI connector is more compact, but lacks latches, and (when using any long and heavy cables) tends to fall out of its socket.
HDMI CABLE
The latest version of the HDMI 1.3a standard at the time of publication of the brochure describes 3 types of connector:
- Standard Single Link (Type A)
- Standard Dual Link (Type B)
- Miniature Single Link (for compact devices) (Type C)
The most common type is the standard Single Link (Type A). Other types of connectors are still rare. The wiring for this connector is shown in Fig. 12, and the purpose of the contacts is summarized in table 2.
Table 2. HDMI connector pinout (Type A, Single Link)
| Cont. | Description | Cont. | Description |
| 1 | Data T.M.D.S 2+ | 2 | Screen for T.M.D.S 2 data |
| 3 | T.M.D.S data 2– | 4 | Data T.M.D.S 1+ |
| 5 | Screen for T.M.D.S data 1 | 6 | T.M.D.S data 1– |
| 7 | Data T.M.D.S 0+ | 8 | Screen for T.M.D.S data 0 |
| 9 | T.M.D.S data 0– | 10 | T.M.D.S+ beats |
| 11 | Screen for T.M.D.S beats | 12 | T.M.D.S beats– |
| 13 | CEC | 14 | (not used) |
| 15 | DDC clocks (SCL) | 16 | DDC Data (SDA) |
| 17 | Ground (for DDC/CEC) | 18 | Power supply +5 V |
| 19 | Hot plug sensor | ||
Rice. 12. Cable part of HDMI Type A connector
INSIDE: TMDS, DDC, HDCP
Video data transfer technologies (TMDS), service channel (DDC), encryption system (HDCP) are similar to those described for the DVI interface.
Cable lengths and maximum resolutions appear to be similar to those for DVI - see fig. 8. The same methods as for DVI can be used to overcome length limitations (Figure 13).
Rice. 13. Optical cable for extending HDMI (Type A) up to 100 meters
In addition to all DVI video modes, the HDMI interface supports:
- since version 1.2 - YUV color space (i.e. Y/Pb/Pr)
- since version 1.3 - xvYCC color space (IEC 61966-2-4, has 1.8 times wider color gamut)
- from version 1.3 - doubled data rate (x2) via TMDS. The mode requires the use of special cables ("category 2") with improved parameters. Cables for all previous versions fall into "category 1". In addition to x2 mode, x1.25 and x1.5 modes are supported.
When using the baud rate doubling mode, starting from version 1.3, the following is possible:
- increase color depth up to 48 bits
- increase the frame rate for standard maximum resolutions up to 120 Hz
- increase maximum resolution
INSIDE: AUDIO TRANSMISSION
Audio data is transmitted along with video over the same TMDS links. The audio stream is “cut” into packets and transmitted in unused sections of the video (during the horizontal and vertical blanking intervals).
Rice. 14. The audio stream is transmitted in packets at video blanking intervals
- since version 1.0 PCM stereo up to 48k, Dolby Digital, DTS is supported
- since version 1.1 DVD-audio is also supported
- Since version 1.2 SACD is also supported
- Dolby®TrueHD and DTS-HD Master Audio™ are also supported as of version 1.3 (at bit rates up to 8Mbps)
INSIDE: CONTROL CHANNEL (CEC)
Many electronics manufacturers announced support for the CEC control channel
An optional CEC (Consumer Electronics Control) link can be used to control consumer electronics. Thanks to it, all devices connected via HDMI (up to 10 pieces) are combined into a control network. 
There are standard control commands (Start, Stop, Rewind, commands for menus, tuners, TV, etc.) that devices can send to each other. This allows you to control one device (say, a Blu-Ray player) from the remote control of another (say, TV), automate some processes, etc. With the release of HDMI 1.3, many electronics manufacturers have announced support for this control channel.
INTERFACE COMPATIBILITY
The HDMI standard stipulates full compatibility of all interface versions (top-down and bottom-up):
- DVI (version 1.0) must be compatible with HDMI (any version). Of course, there is no audio support. Video modes will be limited to those specified for DVI. The connection can be made with an adapter cable (or via an adapter adapter)
- HDMI (any version) must be compatible with HDMI (any version). At the same time, the capabilities of such a system are determined by the capabilities of its "junior" component.
- Any combination of versions of the signal source, display and intermediate devices (repeaters, switches, etc.) is allowed, with the same caveat to the possibilities.
Rice. 15. Adapter cable and DVI-HDMI adapter
Unfortunately, not all devices on the market demonstrate such excellent compatibility. For example, some widescreen home theater displays do not support the RGB color space (required for DVI and HDMI 1.0) and only understand a limited number of video modes (against the minimum required by the standard). At the same time, such displays flaunt the HDMI logo and proclaim support for version 1.3.
Note also that the advanced features of HDMI 1.3a are mostly optional, and therefore it is easy to "comply" with the requirements of this latest version of the standard - it is enough to meet only the minimum requirements (in fact, the requirements for version 1.0). Therefore, when buying equipment, be sure to make sure that it really has the extensions that you need - the number 1.3a in the specification, unfortunately, does not mean anything ...
Links on the Internet:
DVI standard http://www.ddwg.orgHDMI standard
The standard provides simultaneous transmission of visual and audio information over a single cable, it is designed for television and cinema, but PC users can also use it to output video data using an HDMI connector.
HDMI is another attempt to standardize universal connectivity for digital audio and video applications. It immediately received strong support from the giants of the electronics industry (the group of companies involved in the development of the standard includes companies such as Sony, Toshiba, Hitachi, Panasonic, Thomson, Philips, and Silicon Image), and most modern devices High-Resolution Output has at least one such connector. HDMI allows you to transfer copy-protected sound and digital video over a single cable, the first version of the standard is based on a bandwidth of 5 Gb / s, and HDMI 1.3 expanded this limit to 10.2 Gb / s.
HDMI 1.3 is the latest standard specification with increased interface bandwidth, increased clock frequency up to 340 MHz, which allows you to connect high-resolution displays that support more colors (formats with color depth up to 48-bit). The new version of the specification also defines support for the new Dolby standards for lossless compressed audio transmission. In addition, other innovations appeared, in specification 1.3 a new connector was described, which is smaller in size compared to the original one.
In principle, the presence of an HDMI connector on a video card is completely optional; it is successfully replaced by an adapter from DVI to HDMI. It is simple and therefore is included in the kit of most modern video cards. Not only that - on video cards of the HDMI series, the connector is in demand primarily on cards of the middle and lower levels, which are installed in small and quiet barebones used as media centers. Because of the built-in audio, the Radeon » HD 2400 and HD 2600 graphics cards have a definite advantage for assemblers of such multimedia centers.
Based on materials from the company's website iXBT.com
In this article, we will talk in detail about the DVI connector, which can be found in many monitors, TVs and other equipment. Let's delve a little into the history of this popular interface, as well as understand its types and features. And be sure to compare the DVI-connector with some progressive interfaces. This information will be useful to many users, as well as simplify the process of working with equipment and avoid various difficulties when working.
What is DVI output?
A popular connector known as DVI-out (Digital Visual Interface) is intended for high-quality image (video) transmission to various digital devices. As a rule, these are projectors, monitors and televisions.
This video interface was developed by DDWG. Often on the Internet you can find a decoding of these English letters DVI in the following form - a digital video interface. These words are more understandable for many users who are just starting to learn the world of computer and other technology. This connector has a specific color and shape, so it is quite easy to distinguish it from other outputs. Connecting the device to a variety of equipment is quite simple, without requiring mandatory professional skills.
History of the DVI Connector
In 1999, the Digital Display Working Group officially introduced a completely new interface standard at that time called the Digital Visual Interface (DVI). It was developed by leading experts from IBM, Intel, Fujitsu and other well-known corporations who came to DDWG with one goal - to create a truly innovative interface for transmitting a digital video signal to monitors and other image output devices.
The appearance of DVI marked the decline of the VGA era, which has become morally and physically obsolete in 10 years. This allowed not only to improve the quality of the content, but also to significantly increase the resolution of the displays. It is noteworthy that DVI connectors are still relevant to this day, although there are already serious rivals that are gradually replacing the "veteran".
DVI Features
As for DVI, it uses a data format based on PanelLink technology. We are talking about the transfer of information that occurs sequentially, as well as originally implemented by Silicon Image. TMDS technology is used here, when signal transmission occurs differentially in order to minimize differences in levels as much as possible. Three of the channels involved transmit video at speeds up to 3.5 Gbps. If you use a cable up to 10 meters in length, you can transfer a picture in FHD format (1920 by 1200 pixels). When a longer connecting cable is used, then the resolution is “cut down” to HD format.
In some situations, the Display Data Channel (DDC) may be involved. With its help, it will be possible to transfer important information about the display directly to the processor itself, which is installed in the signal source. This includes all detailed data concerning the characteristics of the instrument. We are talking about the brand, production date, model, size and resolution of the display. The source will take this information into account by sending a signal with the optimal settings for a particular screen. If the source does not receive the necessary data, then the TMDS channel may be blocked.
There is support for HDCP, which is an advanced security system. It is also implemented in a more advanced HDMI interface. You can set various levels of content security, based on your own needs. The basic principle of HDCP is that devices connected via DVI exchange passwords with each other. This is how internal encryption works.
It should be noted that the DVI connector is capable of transmitting only an image. As for the sound, it is not transmitted in this case. Therefore, it is necessary to take care of the appropriate channels. It is noteworthy that today for certain video cards there are special adapters that make it possible to simultaneously transmit sound and picture.
Types of DVI outputs
The user may encounter several types of exits. Among them:
- DVI-A
- DVI-I (Single Link)
- DVI-I (DualLink)
- DVI-D (Single Line)
- DVI-D (DualLink)
Therefore, it is easy to guess that the outputs have certain differences. In addition to differences in design, they also have inconsistencies in features. Often the question is raised about the difference between Single link and Dual link. They have many differences. Both options differ from each other in the number of contacts. A double link uses all twenty-four contacts during operation. A single link, which translates as single, has only eighteen contacts. If the user needs more resolution, then the first option is more suitable for him. Single link is suitable for devices that have a resolution of 1920 by 1080. With it, users become much less able.
DVI-A output
This output assumes analog transmission capability only. An additional letter allows the user to guess that "A" means analog. The connector is a plug in a cable or adapter that allows you to connect video devices (analogue) to a DVI-I type output.
DVI output
This connector comes in two types: Single link and Dual link. The first option is very popular and widespread. The additional letter I informs the user that he is integrated. The output is quite often used for digital displays and video cards. Features of this output are that it combines two transmission channels at once. The device combines digital and analog channels. They do not depend on each other, so they do not work at the same time. The task of the device is to decide on its own, thanks to which it will function. The Dual link connector with the letter I carries an analog signal. He has as many as two digital channels. This allows the user to achieve much better image quality and expand their capabilities.
DVI-D output
Here the letter "D" indicates the English word Digital, which can be translated - digital. This option does not have an analog channel. Only digital transmission occurs with this connector. As in previous releases, there is a division into single and double. Single link will limit the user a bit. The resolution cannot exceed 1920 x 1200 (at 60 Hz). This option has only one digital channel. The user will not be able to connect an analog monitor, as well as enjoy a technology called nVidia 3D Vision. But Dual link will help you look at the 3D monitor, increasing the user's capabilities. There are two digital channels here.
DVI-I and DVI-D what is the fundamental difference?
DVI-I supports both digital and analog data transmission, while DVI-D only supports digital.
DVI Connector Compatibility
DVI-A will only be compatible with DVI-A. For transmitting an analog signal. As for DVI-D, it provides the transfer of only digital video content. Its compatibility is possible only with DVI-D. Next, we should mention a universal solution that will work for a variety of devices. It's about DVI-I. In some cases, adapters may be used. But this is possible only when it is provided by the manufacturer of a particular device.
The adapter helps solve the problem, but may affect image quality. There are many types of these devices. There are the following: DVI - HDMI, VGA - DVI and other popular devices. DVI-D and DVI-I cables can work in dual mode (dual link). In this case, the throughput is doubled. For this, additional contacts are used. This solution makes it possible to transmit much more information, which favorably affects the frequency and image of the monitor, which become higher. If you need to use nVidia 3D Vision technology, then a dual link is a must. Also, it is worth knowing that large LCD monitors with high resolution are compatible with the DVI-D Dual-Link connector.
Pinout of DVI outputs
Comparison of DVI connector with HDMI and Display Port
The primacy among the connectors is now at the DP - at the display port. He replaced the previous developments quite quickly. It has excellent bandwidth, and the user gets a lot more new features. The device allows you not to lose quality, and also stands out for its small size. It has already begun to gradually replace dvi and hdmi. However, far from all monitors have exactly those connectors that would fit this new product.
Until there are changes in the system of their production, you will have to wait quite a long time. Most manufacturers are in no hurry to use this device for their equipment. Therefore, even in many modern and popular models, DP has not yet been found. Therefore, dvi and hdmi are not all lost yet. The latter option does an excellent job of transmitting digital video along with sound. The device can be found in popular and new models of equipment. This interface will help you get high resolution. Every year, improved versions appear that not only have excellent throughput, but also give the user much more options. Sound and video do not degrade in quality even with a cable length of 10 meters. The dvi connector also remains famous and in demand. It can be found on many devices, as manufacturers prefer to give it their preference due to its versatility.
Computers and laptops have been equipped with not one, but two or three types of connectors at the same time for 10 years. Ports vary in size and appearance. What type of monitor connection do you prefer? The article also discusses the practical usefulness of connecting two or even three monitors at the same time.
Common, but old types of connectors
VGA (Video Graphics Array): an outdated classic
The blue trapezoidal interface dominated the computing landscape for 25-30 years. It did an excellent job with old CRT displays due to its analog nature. But flat LCD screens appeared - digital devices, then resolutions began to increase and the good old VGA began to lose ground.
Today, it is less and less integrated into video cards, but many devices (consumer players, projectors, TVs) are still equipped with support for the hopelessly outdated VGA. Probably, for a few more years, the “old man” will remain not very desirable, but the de facto ubiquitous standard - if there is any doubt about what cable you can connect a monitor to in a neighboring office, then take VGA.
DVI-I (Digital Visual Interface): another long-lived video interface
In fact, there are several of them: DVI-A, -D and -I, plus their varieties. But when it comes to the most common DVI-I standard, it means analog-to-digital DVI-I Dual Channel - it is this specification that is built into most PCs.
At one time, DVI replaced VGA, which was rapidly becoming obsolete in the mid-2000s. The ability to transmit both analog and digital signals, support for large (in that era) resolutions and high frequencies, the absence of inexpensive competitors: DVI regularly serves as a standard today. But it is unlikely that his active "life" will last more than another 3-4 years.
Resolutions above the minimum comfortable for today FullHD are increasingly found even in low-cost computer systems. With the growth of megapixels, the once serious possibilities of DVI are also coming to an end. Without going into technical details, we note that the peak capabilities of DVI will not allow displaying an image with a resolution of more than 2560 x 1600 at an acceptable frequency (above 60 Hz).
Modern video interfaces
HDMI (High Definition Multimedia Interface) - the king of multimedia
Once awkward for the Russian ear, the abbreviation "HDI" is becoming more and more dense in our lives. Why has HDMI become so popular? It's simple:
- arbitrarily long wires (well, to be honest - up to 25-30 meters);
- sound transmission (even multi-channel!) along with video - goodbye, the need to buy separate speakers for TV;
- convenient small connectors;
- support everywhere - players, "zombie players", projectors, video recorders, game consoles - it's hard to immediately think of technology where there would be no HDMI connector;
- ultra-high resolutions;
- 3D picture. And yes, you can, along with ultra-high resolutions (HDMI 4b and 2.0 versions).
Prospects for HDMI are very bright - development continues, in 2013, version 2.0 specifications were adopted: this standard is compatible with old connector wires, but supports increasingly impressive resolutions and other "tasty" features.
DisplayPort (DP): the connector that's just becoming ubiquitous
And DisplayPort is stunningly beautiful in appearance ...
For many years, computers were rarely equipped with this direct competitor to HDMI. And - despite the fact that DisplayPort was good for everyone: and support for very high resolutions along with a stereo signal; and audio transmission; and an impressive length of wire. It is even more profitable for manufacturers than licensed HDMI: there is no need to pay the developers of the standard those 15-25 cents that HDMI owners rely on.
The DP connector was just unlucky in its early years. However, computers are increasingly equipped with a pair of Display Ports of the modern standard version 1.4. And on its basis, another most popular standard with great prospects was “born”: the “younger brother” of the Display port ...
Mini DP (Mini Display Port)
Along with HDMI and the utterly outdated VGA, the Mini DisplayPort connector is built into almost every computer and laptop. On its side, all the advantages of the "big brother", plus miniature size - the perfect solution for constantly thinning laptops, ultrabooks, and even smartphones with tablets.
Transferring an audio signal so as not to buy separate speakers for the monitor? Please - how many channels do you have? Stereoscopy even in 4K? Yes, let the interface have to stretch all its electronic muscles. Compatibility? There are a wide variety of adapters on the market, almost to any other connector. Future? The Mini DP standard lives and develops.
Thunderbolt: exotic monitor connection options
There are some. For a year now, Apple, along with Intel developers, have been promoting the fast, versatile, but insanely expensive Thunderbolt interface.
Why do monitors also need Thunderbolt? The question remains for many years without an intelligible answer.
In practice, monitors with its support are not so common, and there are big doubts about the justification of Thunderbolt for video signal transmission. Is that the fashion for everything "apple" ...
Unfortunately, the most interesting opportunity to connect screens to a computer (and even supply power to them!) using the USB 3.0 (or, even more interesting, 3.1) interface remains outside the scope of the article. There are many prospects for this technology, and there are also advantages. However, this is a topic for a separate review - and for the near future!
How to connect a new monitor to an old computer?
An "old computer" most often refers to a PC with a single port - VGA or DVI. If a new monitor (or TV) absolutely does not want to be friends with such a port, then you should purchase a relatively inexpensive adapter - from VGA to HDMI, from Mini DP to DVI, etc. - lots of options.
When using adapters, some inconveniences are possible (for example, there is no way to transmit sound or image with a particularly high resolution through VGA), but such a scheme will work properly and reliably.
Video signal without wires (WiDi)!
There are such interfaces, even several. Intel Wireless Display (aka WiDi, or "wi-dai", no matter how strange it may sound for a Russian-speaking reader): an adapter that costs about $ 30 is connected to the USB connector of a TV or monitor (if the technology is supported by the manufacturer).
The signal is sent via Wi-Fi, on the screen - a video image. But this is only in theory, but in practice, the distance and the presence of walls between the receiver and transmitter are significant obstacles. The technology is interesting, it also has prospects - but so far nothing more.
Another wireless video interface is Apple's AirPlay. The essence and practical application is the same as that of WiDI from Intel. Expensive, not very reliable, far from practical.
The solution is more interesting, but not yet widespread - Wireless Home Digital Interface (WHDi). It's not exactly Wi-Fi, although it's a very similar wireless technology. The key feature is a proprietary way to protect against interference, delays and distortion.
Connecting multiple monitors at the same time
Even a novice user can cope with the task of attaching a main or additional screen: the monitor is connected to a PC or laptop no more difficult than a flash drive. Connecting a monitor to a computer is possible only in the right way: the connector simply will not fit into a connector that is not intended for it.
An excellent feature of modern video cards and operating systems is the ability to connect several monitors at once to one signal source (PC, laptop). The practical benefits are enormous, moreover, in two different versions.
1. Image clone mode
The main computer screen is working normally. But at the same time, the image is completely duplicated on a large diagonal TV and / or projector. All you have to do is connect the video cable to both the big screen and the projector. The sound is transmitted along with the image if modern connectors are used (HDMI, Mini DP).
2. Multi screen mode
The resolution of monitors is constantly growing - but there will always be tasks for which it would be desirable to have a wider screen. Calculations in a large Excel spreadsheet, or work immediately with a couple of browsers; design tasks and video editing. Even typing is more convenient when there is also an additional display next to the main one. "Gap" - the frames of the screens in practice interfere no more than the frame of glasses - after a few minutes you simply do not notice them. Gamers also like to use several monitors at once - immersion in the gameplay with this scheme captures noticeably more. By the way, some AMD video cards support up to 6 monitors simultaneously (Eyefinity technology made a lot of noise in the IT community 5 years ago).
Picture: this is how you can call up the connection settings for a second or third monitor: click on "Graphics Settings" from Intel or Nvidia.
How to connect a 2nd monitor to a computer? Insert the cable connector - most likely, the image will instantly be “picked up” by the second screen. If this did not happen, or additional settings / another mode are required - a minute's work in the graphics driver of the video card. To get into this program, just right-click on the icon of the Intel, Nvidia or AMD video driver - depending on which video adapter is installed on the PC, and select "Settings". The video adapter icon is always present in the Control Panel, and in almost all cases, in the Windows tray, near the clock.
Probably, every user of a personal computer or laptop has faced issues of connecting a monitor or TV to it, as well as the state of the quality of the resulting image. And if earlier it was rather problematic to get a high-quality picture on the screen, today this problem does not exist at all. Of course, if your device has a DVI connector. We will talk about it, and also consider other existing interfaces for displaying an image on the screen.
Types of connectors for displaying images on a computer monitor or screen
Until recently, all personal computers had an exclusively analog connection to the monitor. To transfer the image to it, a VGA (Video Graphics Adapter) interface with a D-Sub 15 connector was used. Experienced users still remember the blue plug and 15-pin socket. But, besides it, video cards had other connectors designed to display images on a TV screen or other video device:
- RCA (Radio Corporation of America) - our "tulip". An analog connector designed to connect a video card to a TV, video player or VCR using a coaxial cable. It has the worst transmission characteristics and low resolution.
- S-Video (S-VHS) - a type of analog connector for transmitting a video signal to a TV, VCR or projector with data divided into three channels responsible for a separate base color. The signal transmission quality is slightly better than the "tulip".
- Component connector - an output to three separate "tulips" used to display an image on a projector.
All of these connectors were widely used until the late 1990s. Of course, there was no question of any quality, since both TVs and monitors at that time had a very low resolution. Now we cannot even imagine how it was possible to play computer games while looking at the TV screen with a cathode ray tube.
With the advent of the new century, thanks to the introduction of digital technologies in the development of video devices, RCA, S-VHS and component output became less common. The VGA interface lasted a little longer.
A bit of history
The principle of operation of a conventional video card was that the digital image at the output from it had to be converted into an analog signal by means of a RAMDAC device - a digital-to-analog converter. Naturally, such conversion already at the initial stage worsened the image quality.
With the advent of digital screens, it became necessary to convert the analog signal at the output. Now monitors have also been equipped with a special converter, which, again, could not but affect the image quality.
And here, in 1999, seemingly out of nowhere appeared DVI - the latest digital video interface, thanks to which we can now enjoy the perfect picture on the screen.
The development of this interface device involved a whole group of companies, which included Silicon Image, Digital Display Working Group and even Intel. The developers came to the conclusion that there is no need to convert a digital signal to an analog one, and then vice versa. It is enough to create a single interface, and the image in its original form will be displayed on the screen. And without the slightest loss of quality.
What is DVI
DVI stands for Digital Visual Interface (Digital Visual Interface). The essence of his work lies in the fact that a special TMDS encoding protocol, also developed by Silicon Image, is used to transfer data. The signal transmission method through the digital video interface is based on the serial sending of information previously implemented by the protocol, with constant backward compatibility with the analog VGA channel.
The DVI specification provides for a single TMDS connection at up to 165 MHz and 1.65 Gbps. This makes it possible to obtain an output image with a resolution of 1920x1080 with a maximum frequency of 60 Hz. But here it is possible to simultaneously use a second TMDS connection with the same frequency, which allows you to achieve throughput of 2Gb / s.
With such indicators, DVI left other developments in this direction far behind and began to be used on all digital devices without exception.
DVI for normal user
If you do not delve into the wilds of electronics, then a digital video interface is just a special encoding device that has a corresponding connector on the video card. But how to understand that a computer or laptop has a digital output?
Everything is very simple. Video card connectors with a digital interface cannot be confused with others. They have a specific look and shape that differ from other nests. In addition, the DVI connector is always white, which makes it stand out from the rest.
In order to connect a monitor, TV or projector to a video card, simply plug in the plug of the desired wire and fix it with special manually screwed bolts.
Resolution and scaling
However, neither digital coding nor special video card connectors completely solved the problem of computer compatibility with a monitor. There was a question about image scaling.
The fact is that all monitors, screens and TVs that already have a DVI connector are not capable of outputting a higher resolution than their design provides. Therefore, it often turned out that the video card produced a super-quality picture, and the monitor showed it to us only in a quality limited by its capabilities.
The developers caught on in time and began to equip all modern digital panels with special scaling devices.
Now, when we connect the DVI connector on the monitor to the corresponding output on the video card, the device instantly self-configures, choosing the optimal operating mode. We usually do not pay any attention to this process and do not try to control it.
Video cards and DVI support
The first NVIDIA GeForce2 GTS series graphics cards already had built-in TMDS transmitters. They are widely used today in Titanium cards, being integrated into rendering devices. The disadvantage of built-in transmitters is their low clock frequency, which does not allow high resolution to be achieved. In other words, TMDS do not use the maximum advertised bandwidth at 165 MHz. Therefore, we can say with confidence that NVIDIA at the initial stage failed to adequately implement the DVI standard in its video cards.
When video adapters began to be equipped with an external TMDS operating in parallel with the built-in one, the DVI interface was able to produce a resolution of 1920x1440, which exceeded all the expectations of the company's developers.
In the Titanium GeForce GTX series, there were no problems at all. They effortlessly provide an image with a resolution of 1600x1024.
ATI has taken a completely different path. All of its video cards with DVI outputs also work from integrated transmitters, but they come with special DVI-VGA adapters that connect 5 DVI analog pins to VGA.
Maxtor specialists decided not to bother at all and came up with their own way out of the situation. The G550 series graphics cards are the only ones with a dual DVI cable instead of two signal transmitters. This decision allowed the company to achieve a resolution of 1280x1024 pixels.
DVI connector: types
It is important to know that not all digital connectors are the same. They have different specifications and designs. In our everyday life, the most common types of DVI connectors are:
- DVI-I Single Link;
- DVI-I DualLink;
- DVI-D Single Link;
- DVI-D DualLink;
- DVI-A.
DVI-I SingleLink connector
This connector is the most popular and in demand. It is used in all modern video cards and digital monitors. The letter I in the name means "integrated". This DVI connector is special in its own way. The fact is that it has two combined transmission channels: digital and analog. In other words, this is a DVI + VGA connector. It has 24 digital pins and 5 analog pins.
Given that these channels are independent of each other and cannot be used simultaneously, the device independently chooses which one to work with.
By the way, the first such integrated interfaces had separate DVI and VGA connectors.
DVI-I DualLink Connector
DVI-I DualLink is also capable of transmitting an analog signal, but unlike SingleLink, it has two digital channels. Why is this needed? Firstly, to improve throughput, and secondly, it again comes down to resolution, which is directly proportional to image quality. This option allows you to expand it to 1920x1080.
DVI-D SingleLink Connector
DVI-D SingleLink connectors do not have any analog channels. The letter D informs the user that this is a purely digital interface. It has one transmission channel and is also limited to a resolution of 1920x1080 pixels.
DVI-D Dual Link Connector
This connector has two data channels. Their simultaneous use makes it possible to obtain 2560x1600 pixels at a frequency of only 60 Hz. In addition, this solution allows some modern video cards, such as nVidia 3D Vision, to reproduce a three-dimensional image on a monitor screen with a resolution of 1920x1080 with a refresh rate of 120 Hz.
DVI-A connector
In some sources, the concept of DVI-A is sometimes found - a digital connector for transmitting an exclusively analog signal. In order not to mislead you, we immediately indicate that in fact such an interface does not exist. DVI-A is just a special plug in cables and special adapters for connecting analog video devices to the DVI-I connector.
Digital jack: pinout
All of the listed connectors differ from each other in the location and number of contacts:
- DVI-I SingleLink - has 18 pins for a digital channel and 5 for an analog one;
- DVI-I DualLink - 24 digital pins, 4 analog, 1 - ground;
- DVI-D SingleLink - 18 digital, 1 ground;
- DVI-D DualLink - 24 digital, 1 ground
The DVI-A connector also has its own unique pin arrangement. Its pinout consists of only 17 pins, including ground.
HDMI connector
A modern digital video interface has other types of connecting communications. So, for example, the HDMI DVI connector is in no way inferior in popularity to the listed models. On the contrary, due to its compactness and the ability to transmit audio along with digital video, it has become a must-have accessory for all new TVs and monitors.
The abbreviation HDMI stands for High Definition Multimedia Interface, which means "High Definition Multimedia Interface". It appeared for the first time in 2003 and since then has not lost its relevance at all. Every year there are new versions of it with improved resolution and bandwidth.
Today, for example, HDMI makes it possible to transmit video and audio signals without loss of quality over a cable up to 10 meters long. The throughput is up to 10.2 Gb / s. Just a few years ago, this figure did not exceed 5 Gb / s.
This standard is supported and developed by the world's leading companies producing radio electronics: Toshiba, Panasonic, Sony, Philips, etc. Almost all video devices manufactured by these manufacturers today have at least one HDMI connector.
DP connector
DP (DisplayPort) - the latest connector that replaced the HDMI multimedia interface. With high bandwidth, minimal loss of quality during data transmission and compactness, it was intended to completely replace the DVI standard. But it turned out that not everything is so simple. Most modern monitors do not have the appropriate connectors, and changing their production system in a short time is an impossible task. In addition, not all manufacturers are particularly striving for this, which is why most video equipment is not equipped with the DisplayPort standard.
mini connectors
Today, when more mobile devices are more often used instead of computers: laptops, tablets and smartphones, it becomes not very convenient to use conventional connectors. Therefore, manufacturers such as Apple, for example, began to replace them with smaller counterparts. First VGA became mini-VGA, then DVI became micro-DVI, and DisplayPort dwindled to mini-DisplayPort.
DVI adapters
But what if, for example, you need to connect a laptop to an analog monitor or another device that has a DVI connector to a digital panel with the HDMI, DisplayPort standard? This will help special adapters, which today can be purchased at any electronics store.
Consider their main types:
- VGA-DVI;
- DVI-VGA;
- DVI-HDMI;
- HDMI - DVI;
- HDMI - DisplayPort;
- Display Port - HDMI.
In addition to these basic adapters, there are varieties of them that provide connection to other interfaces, such as USB.
Of course, with such a connection, there is a loss of image quality, even between devices of the same type that support the DVI standard. The adapter connector, no matter how high-quality it is, cannot solve this problem.
How to connect a TV to a computer
Connecting a TV to a computer or laptop is not difficult, but you should determine which interface is equipped with both devices. Most modern television receivers have built-in connectors that support DVI. It can be both HDMI and DisplayPort. If a computer or laptop has the same connector as the TV, it is enough to use the cable that is usually supplied with the latter. If the wire was not included in the kit, you can freely buy it in the store.
The operating system of the computer will independently determine the connection of the second screen and offer one of the options for its use:
- as the main monitor;
- in clone mode (the image will be displayed on both screens);
- as an additional monitor to the main one.
But do not forget that with such a connection, the image resolution will remain the same as provided for by the screen design.
Does cable length affect signal quality?
Not only the signal quality, but also the data transfer speed depends on the length of the cable connecting the device and the screen. Taking into account the modern characteristics of connecting wires for various digital interfaces, their length should not exceed the established indicators:
- for VGA - no more than 3 m;
- for HDMI - no more than 5 m;
- for DVI - no more than 10 m;
- for DisplayPort - no more than 10 m.
If you need to connect a computer or laptop with a screen located at a distance exceeding the recommended one, you must use a special amplifier - repeater (signal repeater), which can also distribute the channel to several monitors.
