High Definition Multimedia Interface (English: High Definition Multimedia Interface, HDMI) is a digital video/audio interface technology. It is a special digital interface suitable for image transmission. It can transmit audio and image signals at the same time. The maximum data transmission speed is 2.25 GB/s, and there is no need to perform digital/analog or analog/digital conversion before signal transmission.
HDMI can be used with Broadband Digital Content Protection (HDCP) to prevent unauthorized copying of copyrighted audio and video content.
The extra space provided by HDMI can be used in the audio and video formats that will be upgraded in the future.
And because a 1080p video and an 8-channel audio signal require less than 0.5GB/s, HDMI still has a lot of margin. This allows it to connect the DVD player, receiver and PRR separately with one cable.
Identification method
[1] HDMI Licensing, LLC released the HDMI specification version 1.4a on March 4, 2010 on behalf of the original HDMI development members. The features include key enhancements for 3D applications, the addition of mandatory 3D formats for broadcast content, and the Top-and-Bottom 3D format.
Since the term "HDMI 1.4" is too broad to show the specific support technology of the device, the use of version number identification methods such as "HDMI 1.4" is completely prohibited in this specification. According to the new version of "Trademark and Logo Usage Specification", HDMI cable manufacturers prohibit the use of version number identification when selling and promoting HDMI version 1.4 standard cables, and the old version of cables should remove all version number identification within one year Labels, instructions, packaging, etc.
For HDMI devices other than cables, all version numbers should be removed before January 1, 2012. Prior to this, manufacturers should apply the version number identification under the premise of clearly displaying the technology used, such as ""HDMI v.1.4 with Audio Return Channel and HDMI Ethernet Channel" (HDMI version 1.4 supports ARC audio return channel and HEC Ethernet Channel), but the general "HDMI v.1.4 compliant" (compatible with HDMI 1.4) is strictly prohibited.
Chinese Canonical Name
There are 5 types of HDMI 1.4 cables. The standard identification methods are:
Standard HDMI Cable Chinese specification name: Standard HDMI cable (up to 1080/60i)
Standard HDMI Cable with Ethernet Standard HDMI Cable with Ethernet
Standard Automotive HDMI Cable Standard Automotive HDMI Cable
High Speed HDMI Cable (support 1080p, DeepColor, 3D)
High Speed HDMI Cable with Ethernet
Background
In April 2002, Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba jointly established the HDMI High-Definition Multimedia Interface Organization, and began to develop a new digital video/audio interface technology that conforms to the high-definition era. After more than half a year of preparation, the HDMI organization officially released the HDMI 1.0 version of the standard on December 9, 2002, marking the official entry of HDMI technology into the historical stage.
The introduction of HDMI technology is not the impulse behavior of these manufacturers on a whim. On the contrary, there are more deep-seated reasons behind the introduction of HDMI technology.
In April 1999, in order to meet the requirements of high-quality graphics in the digital age, the DDWG (Digital Display Working Group) digital display working group based on the patented technology of Silicon Image of the United States, launched a new type called DVI (Digital Visual Interface) The interface aims to unify the digital display interface standard of the new era. This technology has been widely supported by many large companies in the IT industry such as Intel, DELL, HP, IBM, and Microsoft. After more than 3 years of promotion, DVI technology has been rapidly used in the field of computer display output. However, with the development of digital high-definition audio-visual technology, the DVI interface has gradually exposed various problems, and has even become the advancement of digital imaging technology to a certain extent. bottleneck.
The main problems with the DVI interface are:
* The DVI interface considers the PC, which is generally compatible with flat-panel TVs.
* DVI interface lacks support for image copyright protection.
* The DVI interface only supports 8bit RGB signal transmission, which cannot allow a wide color gamut display terminal to exert its best performance.
* For compatibility considerations, the DVI interface reserves a lot of pins to support analog devices, resulting in a large interface and low efficiency.
* The DVI interface can only transmit image signals, and does not consider the support of digital audio signals at all.
Due to the above shortcomings, the DVI interface can no longer better meet the development needs of the entire industry. Therefore, whether it is IT manufacturers, flat-panel TV manufacturers, or many publishers in Hollywood, there is an urgent need for a better interface technology that can meet the future development of the high-definition video industry. It is for these reasons that the HDMI standard is promoted. Birth.
Technical advantages
HDMI can not only meet the resolution of 1080P, but also supports digital audio formats such as DVD Audio, supports 8-channel 96kHz or stereo 192kHz digital audio transmission, and can transmit uncompressed audio signals and video signals. HDMI can be used for set-top boxes, DVD players, personal computers, TV games, integrated amplifiers, digital audio and TV sets. HDMI can transmit audio and video signals at the same time.
HDMI supports EDID and DDC2B, so devices with HDMI have the "plug and play" feature. The signal source and the display device will automatically "negotiate" to automatically select the most suitable video/audio format.
Compared with DVI, the HDMI interface has a smaller volume, and the optimal cable length of HDMI/DVI should not exceed 8 meters. As long as one HDMI cable can replace up to 13 analog transmission lines, it can effectively solve the problem of messy and tangled connections behind the home entertainment system.
Compatibility problems
Receiver (Rx) test
Points for attention in EDID related test items
During the testing process, these items related to EDID testing often fail. If you are familiar with the relevant requirements of the specification, it is relatively easy to pass. For example, relevant specifications require that "Monitor Range Limit Header" and "Monitor Name Header" must be provided in the first 128 bytes of EDID, but if the contents of these two items are less than 18 bytes respectively, they need to end with 0x0A At the same time, fill the remaining bytes with 0x20. Another problem often encountered in EDID testing is that the short video descriptor (SVD) module in EDID cannot be consistent with the submitted capability declaration form (CDF). The CDF indicates that the supported format is in the SVD module of EDID. There is no indication of support, or vice versa.
TMDS signal differential impedance matching
When designing the circuit board, the requirement of TMDS signal differential impedance matching is considered, but it often fails in this test because the selected ESD protection device or the parasitic capacitance of the common mode choke used to suppress EMI is too large. Cause this test to fail. Impedance test chart, you can ask these manufacturers to provide relevant information.
DDC/CEC channel capacitance voltage test
This test has a very high failure rate. The reason for the failure is mostly because the capacitance of the MOSFET device used for level conversion is too large. It is recommended that the MOSFET device Ciss and Coss used on the DDC channel should be below 10pF.
HPD output voltage
In the hdmi protocol, when the hdmi +5V input is 0V, the HPD voltage should be greater than 0V and less than 0.4V. The simplest method here is to connect the +5V voltage of the HDMI input port in series with a 1K resistor and route it directly back to the HPD pin. It is recommended to use a simple triode switch circuit to control the HPD pin, which can actively inform the source device whether the downstream device is ready or inform the source device to restart some verification actions, such as HDCP, etc., which can enhance the device’s performance compatibility.
Video format support
In this test, the video formats that can be supported by all HDMI input ports will be tested for 50Hz ± 0.5% (ie 49.75Hz and 50.25Hz) for devices that support 50Hz, and 59.94-0.5% for devices that support 59.94Hz or 60Hz ( That is, 59.64Hz) and 60+0.5% (ie 60.3Hz) field frequency change support ability. Need to pay attention to these requirements for video format tolerance in software design.
Source test (Tx)
EDID related tests
The HDMI source device must support the "Enhanced DDC" protocol, that is, when reading the EDID information of the receiving device, the segment pointer 0x60 can be used to read the information after the first 256 bytes. Although most customers use 256 bytes of EDID information, the hdmi test will detect the ability to read 4 blocks (128 bytes each), that is, 512 bytes of information. Whether there are multiple pieces of information can be learned from the 0x7E address of the EDID content. When testing, only the ability to support the first 256 bytes is often tested, and the requirement for segment pointers is ignored.
+5V power output
Do not connect a resistor in series with the power output path of the HDMI output port. The specification requires that a load that draws 55mA current is connected during the hdmi Tx test, and then the output voltage is tested. The required voltage is between 4.8V and 5.3V. If a 10 ohm resistor is connected in series and the output voltage is 5-10x0.055 = 4.45V <4.8V, this test fails.
Related DDC/CEC measurements
When dealing with the consumer electronics control (CEC) pin of the HDMI port, that is, the 13th pin of the HDMI port, if the product does not support the CEC function, this pin can be left floating. However, some products often connect this pin to the general-purpose pin of the main processing chip even though it does not support the CEC function. It is ready for future expansion. At this time, you need to pay attention to some restrictions on the electrical performance and physical connection of this pin. For example, the capacitance needs to be less than 100pF, etc., otherwise the hdmi test will fail.
advantage
Advantages of using HDMI video interface
The advantages of HDMI over existing analog video interfaces such as composite, S-Video and component video:
1. Quality: HDMI is a digital interface. Since all analog connections (such as component video or S-video) require no loss when converting from analog to digital, it can provide the best video quality. This difference is particularly noticeable at higher resolutions, such as 1080p. Digital video will be clearer than component video, eliminating the softness and smearing found in component video. Small, high-contrast details such as text take this difference to the extreme.
2. Ease of use: HDMI integrates video and multi-channel audio in a single cable, thereby eliminating the cost, complexity and confusion of the multi-cable used in the current A/V system. This is especially useful when upgrading or adding equipment.
3. High intelligence: HDMI supports two-way communication between video sources (such as DVD players) and DTV, realizing new functions, such as automatic configuration and one-key playback. By using HDMI, the device automatically transmits the most efficient format (such as 480p vs 720p, 16:9 vs 4:3) for the connected display? Eliminates the need for consumers to scroll through all format options to guess the best viewing format.
4. High-definition content ready: HDMI devices that support HDCP can access advanced high-definition content, which brings us a little comfort. HD-DVD and Blu-ray have delayed the activation of the image boycott mark (also known as the content protection mark) for today's high-definition movies to help minimize potential problems caused by conversion, but it is expected that this mark will be activated within a few years , Which means that future high-definition movies will not be able to be played in high-definition through unprotected interfaces (such as analog components).
application
HDMI was first used in 2002 to obtain a higher-quality video and audio digital system to meet the needs of users. Many different TV, computer and electronic product manufacturers have adopted the HDMI specification. These standards respectively describe the association’s electronics manufacturing companies in cooperation with major music and movie distribution companies. The EIA/CEA-861 standard used by HDMI defines video waveforms and formats, auxiliary data, compressed and uncompressed audio for transportation, and LPCM audio.
There are two different types of leads on the market, namely category 1 and 2. These categories only apply to version 1.3 and higher, which was in 2008. Category 1 cables bear standard HDMI cable labels and are suitable for sending 720p or 1080i video and audio signals. Information in the second category is also considered fast speed clues, and can carry video and audio signals, 720p and 1080i and 1600P. The classification of two HDMI cables is the only type that is guaranteed to work with cables longer than 16 feet.
Due to the attenuation of the signal, the long lead should have a certain limit. Cables that are too long transmit very weak digital signals, resulting in flickering images on the screen. Use HDMI extenders, equalizers or repeaters to avoid the problem of signal loss. These devices can be connected to each other with cables, thus extending the length of the cable without losing signal strength. The maximum length that can be used depends on the type of cable. In Category 5 or Category 6, the total cable length can be increased to 164 feet. If the expansion is based on optical fiber, the total cable length increases to 328 feet.
Buying skills
step 01: To confirm the version of the HDMI cable, pay attention to the version of the HDMI cable. There are three common versions 1.3, 1.4 and 2.0. It is recommended to buy version 2.0 HDMI cable with a bandwidth of up to 21.8Gbps, support 3D transmission, can meet higher resolution, refresh rate and color depth, can support HD playback above 1080P, and compatible with 1.3 and 1.4 functions.
step 02: Pay attention to the size of the HDMI interface
HDMI interfaces are divided into standard ports and mini ports. Due to the size limitation, the HDMI ports on HD MP4 are basically mini ports, so if you choose HDMI cable for HD MP4, you must find the standard-mini HDMI cable, otherwise it will not be plugged in.
step 03: The HDMI cable is not as long as possible
The theoretical transmission distance of a single HDMI cable is 7-8 meters, but in actual use, it does not need to be that long. Before buying, it is best to measure the required length, as long as a margin of 50 cm is enough for the measurement result.
step 04: Choose brand HDMI cable, more worry-free
If you find it difficult to judge which HDMI cable is better or worse with your own eyesight, the easiest way is to choose a branded HDMI cable, such as eda, Yabao, Fujicables, Monster and other brands. The quality is quite guaranteed!
step 05: Avoid excessive bending of HDMI cables
During the use of the HDMI cable, avoid excessive bending of the cable. For example, frequent folding and winding may damage the core or shielding layer of the line. Generally bend along an arc without damaging the cable.
