Introduction
The entertainment industry has accomplished great things in the with respect to the technology of execution audio and video. Today, it is already possible to have in the house a “private cinema”, using, for example, televisions or projectors high-definition along with an audio system powerful and crystal clear. Join it to the availability content mutimídia on the Internet, and you will have a true entertainment center in the house. The only problem this whole story may be the confusion of cables to interconnect the appliances, but the HDMI(acronym for High-Definition Multimedia Interface) appears to give a little help on this question.
The HDMI is a connection technology capable of handling audio and video at the same time, that is, it is not necessary to have a separate cable for each thing. In addition, the entire transmission the HDMI cable is made by means of digital signals, which makes it the technology is able to transmit video and audio of the highest quality. That such know more about the advantages of HDMI and understand a little of your operation? Is what you’ll see below.
What is HDMI?
HDMI it is a technology of connection of audio devices and the video that has everything to replace the existing standards until then. Behind its development is a team of the giants of the electronics industry such as Sony, Philips, Toshiba, Silicon Image, etc. With this technology, it is possible, for example, to connect a player Blu-ray a high-definition TV and have as a result the images excellent quality. By means of an HDMI cable can transmit audio and video signals. In other standards it is necessary to have, at least, a cable for each thing.
But, the advantages of HDMI are not limited to this. This is a technology that transmits signals in a fully digital. Thanks this, it is possible to have images of excellent quality and high resolutions (1080p, for example), including the largest that the supported by the technology, DVI (Digital Visual Interface), that replaced the default VGA for connections to monitors on computers (learn more about DVI and VGA).
The connector of the HDMI cable also takes advantage of the relationship the other standards, since it has a reduced size and fitting easy, similar to the USB connectors. In fact, the industry defined two types of connectors that are initially: the HDMI type A and HDMI type B, with 19 and 29 pins, respectively. The type A connector is the most common market, since it cannot meet the existing demand, including being compatible with the technology DVI-D. in This case, just that one end of the cable is DVI-D, and the other, HDMI. The HDMI connector type B is intended for higher resolutions and can work with the scheme to dual link, which doubles the frequency pixel clock (issue addressed below), causing the transmission double your capacity.
Operation of the HDMI
The quote from the technology DVI on the previous topic does not it was mere chance. Both the DVI and the HDMI to make use of a protocol called Transition Minimized Differential Signaling (TMDS), which the make, up to a certain point, similar. In the HDMI, are used three-channel TMDS for transmission of information audio and video. The devices that initiate the transmission are called sources. In turn, the devices that receive the signal of the transmission are called sinks.
The technology TMDS exerts an extremely important function in the transmission of the HDMI because, although the signal is all digital, this does not mean that it is free from faults and interference. With the channels TMDS, the data transmission can be performed encoded making it protected. This is possible because the channel TMDS uses a scheme of cancellation. In it, the signal is duplicate, however the second signal is inverted. The device the receiver receives both the signals and compares them. The differences found this comparison allow us to identify the changes undue – that is, the noise from the transmission – and to discard them.
When transmission is initiated, the three-channel TMDS are used for the sending of video data, the so-called Video Data Period. Every channel sends 8 bits at a time, totaling 24-bit. This is done at a frequency called the pixel clock that varies from 25 MHz to 165 MHz. In the case of transmissions that do not reach the 25 MHz, as what happens in signs PAL and NTSC, it is made use of a technique of repetition of pixels. With this mode of operation, the HDMI can transmit more of 165 million pixels.
The illustration below is accompanied by a table that shows the pins of the HDMI connector type A. Note that each channel TMDS uses two pins, for a total of 6. There are also a couple of pins used to the frequency of the TMDS, the TMDS clock. Each the pair is protected from interference by a pin shield:
Resolution
When the subject is HDMI (or other related technologies, such as the HDTV – High-Definition Television), it is common the mention of resolutions such as 720p and 1080p. But, what does this mean? Although it looks complicated, these classifications simply facilitate the identification of the amount of pixels (in a few words, a pixel is a dot that represents the smallest part of the image on a screen) supported by the device, in addition to the use of progressive scan or interlaced scan. In progressive scan, all lines of pixels of the screen are updated simultaneously. In turn, in mode interlaced scan, the first lines pairs receive update and then the odd lines (ie, is a scheme type: line yes, line no). In general, the mode progressive scan offers better image quality.
Thus, the letter ‘p’ existing in 720p, 1080p and other resolutions indicates that the mode used is progressive scan. If it is used for interlaced scan, the letter used is ‘i’ (for example, 1080i). The number, in turn, indicates the amount of rows of pixels in the vertical. This means that the 1080p resolution, for example, with 1080 lines vertical, and works with progressive scan. Here are some common resolutions:
- 480i = 640×480 pixels with interlaced scan;
- 480p = 640×480 pixels with progressive scan;
- 720i = 1280×720 pixels with interlaced scan;
- 720p = 1280×720 pixels, with progressive scan;
- 1080i = 1920×1080 pixels with interlaced scan;
- 1080p = 1920×1080 pixels with progressive scan.
You must have already heard of the term Full HD (High Definition). This expression, whose interpretation would be something like “High-Definition” the Maximum, it indicates that the screen work in the maximum resolution, that is 1080p. This means that the device will be able to run in the highest quality videos from a disc , Blu-ray, for example – ready for this level of resolution.
Learn more about resolutions the screen here.
Versions of HDMI
The HDMI technology has gone through several revisions in their specifications since the release of the first version. The advantage this is that each version adds improvements to the technology. On the other hand, this causes confusion and, in certain situations, can cause the obstruction of the sending of the signal. This problem can occur, for example, if the receiving device working with a version lower than the version used by the sending device. For to deal with this possibility, the industry has developed techniques that guarantee the transmission of the data. The difference is that, if the transmission require some existing feature in version latest, the device with the previous version may not be able to use it.
The following is a brief description of the main characteristics of the reviews existing up to the publication of this text in AbbreviationFinder:
– HDMI 1.0: officially launched at the end of 2002, the first version of HDMI is characterized by the use of single cable for video and audio transmission with a rate of data transmission 4,95 Gb/s to a frequency 165 MHz. It is possible to have up to 8 audio channels;
– HDMI 1.1: similar to version 1.0, however with the addition of compatibility to the standard of the DVD-Audio. Launched in may 2004;
– HDMI 1.2: added support for the audio formats of the type One Bit Audio, used on, for example, SACD (Super Audio CD). Support is included for the use of the HDMI on PCs and the new color schemes. Released in August 2005;
– HDMI 1.2: released in December 2005, this revision it has adopted the specifications for Consumer Electronic Control (CEC), and specific features for remote control;
– HDMI 1.3: in this version, the HDMI now supports frequency up to 340 MHz, allowing for transmissions of up to 10.2 Gb/s. in addition, version 1.3 allows the use a wider range of colors and support technology Dolby TrueHD and DTS-HD Master Audio. This version also allowed the use of a new mini (HDMI type C – mini), appropriate cameras video portable, and eliminates a timing issue between the audio and video (lip sync). The release the HDMI 1.3 if you gave in June 2006;
– HDMI 1.3 a and 1.3 b: released in November 2006 and October 2007, respectively, these revisions include slight changes in the specifications of version 1.3 and with the addition some tests, including in relation to the HDCP, which is covered ahead.
HDMI 1.4
This version was announced in may 2009 and offers so many new developments that could even be called 2.0. Here are its main features:
– Ability to work with resolutions up to 4096×2160 pixels;
– Compatibility with a larger number of colors;
– Support an audio return channel (Audio Return Channel – ARC);
– Possibility of transmission by means of Ethernet connections up to 100 Mb/s (HDMI Ethernet Channel – HEC), allowing that interconnected devices to share access to the internet;
– Better support for technologies of 3D images;
– Standardization for transmission in vehicles (DVD players bus, for example).
And it does not end there, because the standard brings with it new types of cable:
– Standard HDMI Cable: standard cable that supports transmissions 1080i;
– High Speed HDMI Cable: cable for transmissions of 1080p, including support for a greater number of colors and 3D technologies;
– Standard HDMI Cable with Ethernet: standard cable with support the Ethernet technology;
– High Speed HDMI Cable with Ethernet: cable for transmissions high speed with support to technology-Ethernet
– Automotive HDMI Cable: appropriate cable for transmissions in vehicles.
The HDMI 1.4 also introduces a new type of connector (HDMI type D – micro) 19 pin, which is so small it can be easily used in portable devices such as digital cameras and smartphones.
Despite offering interesting features, the HDMI 1.4 has been criticized by raising the number of types of cables and connectors, or is, by increasing the complexity for the user. On the other hand, the new types of cables can make the cost of this accessory is less to the consumer, since this will not be required to pay more for cables that support the features that it does not use. In addition, the connector type D facilitates the integration with portable devices.
Content protection with HDCP
A lot of people “twist the nose” when he discovers what HDCP means and what it represents to the HDMI technology. This is an acronym for High-Bandwidth Digital Copy Protection, a technology developed by Digital Content Protection, LLC (owned by Intel) with for the purpose of preventing the illegal distribution of content. Your operation occurs, basically, in the following way: the source (the sending device) communicates with the sink (receiving device) by through a channel called a Display Data Channel (DDC) to meet your configuration and obtain an authentication code. These data are stored in a chip called the Extended Display Identification Data (EDID). If the code on both machines they are compatible, the source gets a new code and sends to the sink. The sending and received of information of a device to the other is done on the basis of this code. This code it is checked at a given interval and, if any abnormality is found, the transmission is interrupted. This can occur, for example, if a third device attempts to receive the data of the connection.
The industry has implemented this scheme in the HDMI to prevent piracy, but for a lot of people this is not the best way to deal with the problem and thus all the strict security measures, the user honest is that it can be harmed. If the obtaining key authentication fails for any reason, even the user is not taking any responsibility about it, he will not be able to view your video. In some cases, the user discovers that if you disconnect and reconnect the devices maybe everything works, a practice unfortunate for a technology so advanced.
Ending
The standard VGA has been, for more than 20 years, the main means of connection monitors to computers, but gave in your “reign” the DVI standard (learn more about standards VGA and DVI in this article). Apparently, the HDMI was able to do the same refers to the connections between TVs and devices running video, as a player of Blu-ray, for example.
