HDMI

Introduction

In the entertainment industry has made great achievements with regard to technologies for implementing audio and video. Today, we have in place a particular film, "using, for example, TVs or projectors for high resolution combined with a powerful audio system and lens. Add this to the availability of content mutimídia on the Internet, and you have a true home entertainment center. The only problem in this whole story may be the confusion of cables to interconnect the devices, but the HDMI (acronym for High-Definition Multimedia Interface) is to give a help in this matter.

The HDMI connection is a technology capable of dealing with audio and video at the same time, that is, you do not need a separate cable for each thing. Furthermore, all transmission of HDMI is done by digital signals, which makes the technology able to transmit video and audio of the highest quality. Know that most benefits of HDMI and a little understanding of its functioning? This is what you see below.

What is HDMI

HDMIHDMI logo is a standard connection for audio and video devices that have anything to replace the existing standards so far. Behind its development is a team of electronics industry giants such as Sony, Philips, Toshiba, Silicon Image, among others. With this technology, it is possible, for example, connect an HD-DVD player to a TV with high resolution and have as a result of excellent image quality. Through an HDMI cable, you can transmit video and audio signals. In other patterns, you must have at least one cable for everything.

But the advantages of HDMI are not limited to this. This is a technology that transmits signals in a fully digital. As a result, images can be of excellent quality and high resolutions (1080p, for example), even larger than those supported by technology DVI (Digital Visual Interface), which is replacing the standard VGA monitors for connections on computers.

The connector of the HDMI cable also takes advantage over other standards, as have small size and easy to fit, similar to USB connectors. Indeed, the industry defines two types of connectors: HDMI to HDMI type A and type B, with 19 pins and 29, respectively. The connector type A is the most common market, since it can meet all the demand exists, is also compatible with DVI-D technology. In this case, just a tip of the cable is DVI-D and the other, HDMI. The HDMI connector is Type B for higher resolutions and can work with the dual-link scheme, which doubles the pixel clock frequency (issue addressed below), causing the transmission to double its capacity.

Operation of HDMI

The quote on the topic of technology DVI earlier was not mere coincidence. Both the DVI as the HDMI make use of a protocol called Transition minimized Differential Signaling (TMDS), which make them to some extent similar. With HDMI, TMDS three channels are used for the transmission of video and audio information. The devices that begin transmission are called sources. In turn, devices that receive the signal of transmission are called sinks.

The TMDS technology plays a major role in transmitting HDMI extremely important because, although the signal is all digital, that does not mean that it is free of faults and interference. With TMDS channels, data transmission can be so coded, making it protected. This is possible because the channel TMDS uses a scheme of cancellation. There, the signal is doubled, but the second signal is inverted. The device receives both signals and compares. The differences in comparison identifying undue changes - that is, the noise of the transmission - and discard them.

When the transmission is started, the three TMDS channels are used for transmitting video data, called the Video Data Period. Each channel sends 8 bits at a time, totaling 24 bits. This is one called pixel clock frequency that varies from 25 MHz to 165 MHz in the case of transmissions that do not reach the 25 MHz, as the case in NTSC and PAL signals, is done using a technique of repetition of pixels. With this operation, the HDMI can transmit more than 165 million pixels.

The illustration below is accompanied by a table that shows the pins of the connector HDMI type A. Note that each TMDS channel uses two pins, totaling 6. There is also a pair of pins used for the frequency of TMDS, the TMDS clock. Each pair is protected from interference by a shield pin:

HDMI type A connector

Signal Via
TMDS 1 + date2
2 TMDS Shield date2
3 TMDS date2 -
4 TMDS Data1 +
5 TMDS Data1 Shield
6 TMDS Data1 -
7 TMDS Data0 +
8 TMDS Data0 Shield
9 TMDS Data0 -
10 TMDS Clock +
11 TMDS Clock Shield
12 TMDS Clock -
13 CEC
14 Reserved
15 SCL
16 SDA
17 DDC / CEC Ground
18 +5 V Power
19 Hot Plug Detect

 
Versions of HDMI

HDMI in the back of a TVA HDMI went through several revisions in its requirements since the release of the first version. The advantage is that each version adds improvements to technology. Moreover, this causes confusion and, in certain situations, can cause the prevention of transmission of the signal. This problem may occur, for example, if the device work with a version lower than the version used by the device issuer. To address this possibility, the industry has developed techniques that ensure the transmission of data. The difference is that if the transmission require some existing feature in the latest version, the device with the previous version can not use it.

The following is a brief description of the main features of the revisions to the existing publication of this text in InfoWester:

HDMI 1.0: officially launched in late 2002, the first version of HDMI is characterized by using single cable for transmission of video and audio with a data transmission rate of 4.95 Gbps with a frequency of 165 MHz is possible to have 8 channels of audio;

HDMI 1.1: similar to version 1.0, but with the addition of compatibility to the standard DVD-Audio. Launched in May 2004;

HDMI 1.2: Added support for audio formats of the type One Bit Audio, used, for example, SACD (Super Audio CD). Included support the use of HDMI in PCs and new color schemes. Launched in August 2005;

HDMI 1.2a: launched in December 2005, this review has adopted the specifications Consumer Electronic Control (CEC) and specific resources for remote control;

HDMI 1.3: this version, HDMI has the support of up to 340 MHz frequency, allowing transfers of up to 10.2 Gbps. In addition, version 1.3 allows for a wider range of colors and support for Dolby TrueHD and DTS-HD Master Audio. This version also allowed the use of a new mini-connector, suitable for portable video cameras, and eliminates the problem of synchronization between the audio and video (lip sync). The release of HDMI 1.3 was in June 2006;

HDMI 1.3a 1.3b: launched in November 2006 and October 2007 respectively, these revisions have minor changes in specifications of version 1.3 and with the addition of some tests, even in the HDCP, because the next topic.

For HDCP content protection

Many "twists the nose" when they discover what HDCP means and what it represents for the HDMI. This is an acronym for High-Bandwidth Digital Copy Protection, a technology developed by Digital Content Protection, LLC (owned by Intel) in order to prevent the illegal distribution of content. Its operation is done, basically, as follows: the source (transmitter device) communicates with the sink (receiving device) through a channel called the Display Data Channel (DDC) to know the shape and get a code for authentication. These data are in a chip called the Extended Display Identification Data (EDID). If the code on both devices are compatible, the source obtains a new code and sends the sink. Sending and receiving information from one device to another is based on that code. This code is checked to a certain range, and if any abnormality is found, the transmission is interrupted. This can occur, for example, if a third attempt to get the device's data connection.

The industry has implemented this scheme in HDMI to prevent piracy, but for many people, this is not the best way to deal with the problem and thus all the stringent security measures, you can be honest is undermined. If obtaining the key authentication fails for any reason, you do not even taking any responsibility for it, he can not view your video. In some cases, you find that you disconnect and reconnect the devices, maybe it works, a practice unfortunate for a technology so advanced.

Resolution

When it comes to HDMI (or other related technologies such as HDTV - High-Definition Television) is a common statement of resolutions to 720p and 1080p. But what that means? Although it looks complicated, these classifications simply facilitate the identification of the number of pixels supported by the device, besides the use of progressive scan or Interlaced scan. With progressive scan, all rows of pixels on the screen are updated simultaneously. In turn, the Interlaced scan mode, the first lines pairs receive updates, then the odd lines (ie, a schema is like: yes line, not online). In general, the progressive scan mode offers better image quality.

Thus, the letter 'p' existing 720p, 1080p and other resolutions indicates that the method used is progressive scan. If used Interlaced scan, is used the letter 'i' (for example, 1080i). The number, in turn, indicates the number of rows of pixels horizontally. This means that the 1080p resolution, for example, has 1,080 horizontal lines and work with progressive scan. Here are some resolutions:

480i = 640x480 pixels with Interlaced scan;
480p = 640x480 pixels with progressive scan;
720i = 1280x720 pixels with Interlaced scan;
720p = 1280x720 pixels in progressive scan;
1080i = 1920x1080 pixels with Interlaced scan;
1080p = 1920x1080 pixels with progressive scan.


The VGA standard was, for over 20 years, the primary means of connecting computers to monitors, but now is giving his "reign" to the standard DVI (more on the standard VGA and DVI in this article). Is the HDMI will do the same for connections between TVs and devices for implementing the video (as a player, HD-DVD, for example)? The answer is: maybe.

The HDMI is already present in many devices that work with high-quality images (such as the PlayStation 3 console from Sony) and is quite common in current systems for home theater. But it is too early to say whether this technology will be dominant in the market. There are several reasons for this, including: implementation guy (mainly because of the payment of royalties), due to possible confusion of the various revisions and the emergence of similar technologies as the standard DisplayPort, Unified Display Interface (UDI) and WirelessHD (wireless ).

Anyway, it is worth investing in equipment compatible with HDMI (especially with the current latest revision). It may be that the pattern is not very long in the market, but if that happens, certainly not sumirá quickly.