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With the development of audio and video products and formats, especially HDTV products are increasingly accepted by ordinary consumers, the transmission pressure of large amounts of data brought by high-definition format programs, the chaos of wiring caused by more high-fidelity channels, and increasingly important The copyright protection of high-definition audio and video programs has raised new requirements for technological development.
At present, the interface specifications of mainstream digital home appliances can only transmit compressed or uncompressed digital video signals, and audio signals require a separate interface to connect, which brings a lot of inconvenience to ordinary consumers during use. In September 1998, Intel announced the establishment of the Digital Display Working Group (DDWG) on its Developer Forum (IDF). And in April 1999, DVI (Digital Visual Interface; Digital Video Interface) was proposed to become a common display device interface for computers and TVs. The emergence of DVI formally provided a quick solution of "digital output → digital input". Due to the many advantages of digital transmission, today's PC display cards and monitors are gradually changed to DVI as the main output and input interface. However, the DVI interface is only maintained in the transmission of video signals, and does not include the transmission of audio signals.
At the beginning of this century, under the approval of most video studios, producers, many famous TV program suppliers, cable TV industry and most consumer electronics manufacturers in Holly Wood, it was advocated by Silicon Image and united with Sony, Hitachi, Panasonic , PHILIPS, THOMSON (RCA), Toshiba and other well-known consumer electronics manufacturers established working groups to jointly develop, and signed an agreement to recognize the introduction of high-definition digital multimedia interface HDMI (High-DefiniTIon Digital MulTImedia Interface; HDMI) interface standard, And officially announced the HDMI Version 1.0 specification in December 2002. Shortly after the introduction of the interface, the DVD Forum facilitated the approval of HDMI as one of the standard signal transmission standards in October 2003. The HDMI 1.1 specification was released in May 2004, and the 1.2 standard was released in August 2005. The current highest version is the 1.2a standard released on December 14, 2005.
Second, the advantages of HDMI in application
Sufficient bandwidth requirements: As we all know, the amount of data required for digital high-definition video and the corresponding data transmission volume is very large. The data interface and cable connecting the signal source and the receiving end must be able to provide more bandwidth than the digital high-definition video playback requires , We can see the real high-definition video images. The digital bandwidth required for HDTV 1080p high-definition mode is between 2.0Gbps and 2.2Gbps, which is an eight-channel (7.1 sound system) audio transmission requirement, but the total bandwidth requirement does not exceed 4Gbps. The HDMI 1.0 standard can provide 5Gbps transmission bandwidth between HDMI interfaces, so HDMI's current protocol can fully meet the requirements of high-definition format program playback.
However, HDMI is not only as simple as supporting digital HD, and the HDMI standard is only version 1.2a. The high standard 1080p of mainstream digital HD is completely supported on its existing basis, but in the future, with the digital HD standard Further improvement, I believe that the new specification will greatly improve the bandwidth, USB1.0 to USB2.0, IEEE1394a to IEEE1394b bandwidth improvements are a good precedent. It can be deduced from this that the larger expansion space of HDMI will still be able to meet the greater bandwidth requirements of future audiovisual products.
Audio and video fusion: This is the most exciting place of HDMI interface. Through it, we can directly enjoy the shock effect brought by digital high-definition without transmitting audio and video separately. It is also the only one that can provide audio and video at the same time. Digital high-definition transmission interface.
Unprecedented simplicity: Imagine the vastness of the project in which we usually connect audiovisual equipment. Generally speaking, we need 3 color-difference lines for video, and audio will be more and more complicated depending on the system we use. For example, 5.1 system, we will use 6 connections, and 7.1 will need 8 more Connections. Facing a lot of complicated wiring, I believe everyone will feel tired. And now, corresponding to the HDMI interface, we only need one connection to complete all the work, and HDMI can support plug and play, maximizing your work and keeping your home theater system away from the trouble of many connections.
Although the HDMI interface is powerful, it is very compact. It is only the size of the usual USB interface. Compared with the huge DVI interface, the compact design makes it easier to install into the device. For example, high-definition DV is very good. A space for displaying characteristics.
Good compatibility: There is no denying that the number of devices that provide DVI interface support is far greater than the number of devices that provide HDMI interface. Because HDMI started much later than DVI, in order to promote the HDMI interface more smoothly, HDMI is fully compatible with DVI (because their principles are similar, HDMI is compatible with DVI on the pins, but uses a different package), through DVI- HDMI interface adapter, we can easily use the HDMI interface
Excellent anti-attenuation capability: HDMI has excellent anti-attenuation capability in data transmission, which makes it more advantageous than DVI and other methods in long-distance transmission, and the excellent anti-attenuation capability of HDMI is also reflected in its cable Not to be picky. The performance of ordinary HDMI cables is similar to that of high-priced HDMI cables. This feature allows consumers to save a lot of money on wire materials. The excellent characteristics of HDMI make it perform well under the limit of cable length. HDMI does not specify the distance limit of the cable, which is why many Internet say that HDMI has no length limit. At present, the HDMI copper cables provided by general cable manufacturers are within 15 meters. On the one hand, there is a good reliability guarantee, and on the one hand, the price is more conducive to consumer acceptance. This distance range is far beyond the 5 meters that DVI can guarantee. distance. Someone once made an HDMI cable up to 50 meters long. It is said that it can also be used for basic use, which shows that its anti-attenuation ability is indeed good. However, this method is generally not recommended. For longer distance transmission, it is recommended to use optical fiber or repeater connection with signal amplification function to ensure high-quality signal transmission.
Support for more primary color depth digital video signals: DVI is produced on the PC platform, and the color depth of the primary colors supported is limited to True Color's 24bit, that is, the three primary colors each have 8bit digital video signals, and the current digital TV requires 36bit High-fidelity pictures, that is, the three primary colors are required to have 12-bit digital video signals. Currently, DVI cannot meet this requirement, and HDMI can support 12-bit digital video signals. The emergence of HDMI allows us to enjoy the richer color levels and more shadow details.
3. General introduction of HDMI interface
The general HDMI connector is divided into Type A and Type B. Usually the Type A interface carries all HDMI signals, including a single TMDS link. The Type B connector is slightly larger and carries two TMDS links. It is generally used for relatively demanding computer displays.
Generally speaking, Type A connectors can meet the transmission requirements below 165KHz, and beyond 165KHz, Type B connectors with dual TMDS Link are required. And HDMI dual-link is compatible with DVI 1.0 dual-link structure.
As shown in Figure 1, it is a schematic diagram of the structure of Type A socket and plug.
Among them, the shell of the socket has a locking device to shield electromagnetic interference; when the plug is inserted, the elastic locking device will automatically pop up.
As shown in Figure 2, it is a schematic diagram of the structure of Type B socket and plug. 
Similarly, there is a locking device on the shell to shield electromagnetic interference; when the plug is inserted, the elastic locking device will automatically pop up and lock.
The basic principle of HDMI interface
1. Overview