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What is DHMI interface

2021-01-22

Introduction to HDMI interface

 

1. HDMI interface

HDMI is a new generation of multimedia interface standard. Full name (high-definition Multimedia Interface), High definition Multimedia Interface. HDMI can transmit video and audio simultaneously, simplifying the interface and wiring of the device. At the same time, it provides higher data transmission bandwidth, which can transmit uncompressed digital audio and high resolution video signals. HDMI interface is shown in the figure below:
HDMI is downward-compatible with DVI (a digital video interface that can only be used to transmit video, not audio at the same time). Both DVI and HDMI interface protocols use TMDS standard to transmit audio and video data in the physical layer. DVI interface is shown in the figure below:

 

HDMI (High definition multimedia interface) has become the global connectivity standard for the HDTV and consumer electronics industries. It is the first and only digital interface available in a single interface combining uncompressed HD video, multi-channel surround audio, and intelligent command data. For customers, it makes it extremely simple to connect to HD devices while providing consistent and high performance delivery of the latest product features. The HDMI standard has been adopted by thousands of manufacturers around the world and is used in hundreds of millions of consumer products -- not only home theater components, but also computers and peripherals, mobile devices, vehicle systems, and more.

 

2. The interface type of HDMI

HDMI interfaces are divided into Type A, Type B, Type C, Type D and Type E, as shown in the figure below. Type A and Type D are the most commonly used. Type D is also called Micro HDMI, Micro HDM Interface.

The HDMI Type A interface is A total of 19 pins, 13.9 mm wide and 4.45 mm thick. The vast majority of audio-visual devices used in daily life are equipped with this interface. For example: Blu-ray player, Mi box, laptop, LCD TV, projector and so on.

HDMI Type B is relatively rare in life and is mainly used in professional level applications. HDMI B interface with 29pin, width of 21 mm. The HDMI B Type delivers nearly twice as much data transfer capacity as the HDMI A Type, equivalent to A DVI Dual-Link.

HDMI Type C, often referred to as Mini HDMI, is designed primarily for smaller devices. The HDMI C Type also uses a 19pin, but is only 10.42mm wide and 2.4mm thick. It is mainly used in portable devices, such as digital cameras, portable players and other devices.

HDMI Type D is also known as Micro HDMI. The HDMI Type D interface is also 19pin and is only 6.4 mm wide and 2.8 mm thick. It is mainly used in small mobile devices. For example: mobile phone, tablet, etc.

HDMI Type E is mainly used for audio and video transmission of in-car entertainment systems. Due to the instability of the interior environment, the HDMI E Type is designed for shock resistance, moisture resistance, high strength resistance, and wide temperature range. In the physical structure, the mechanical locking design can ensure the reliability of contact.

 

3. The function of each 19pin pin foot

HDMI signal pin definition pin signal pin signal pin signal   1 Data 2 + 2 Data 2 masking 3 Data 2 -   4 Data 1 + 5 Data 1 masking 6 Data 1-   7 Data 0 + 8 Data 0 masking 9 Data 0-   10 The clock + 11 The clock screen 12 The clock -   13 CEC 14 keep 15 SCL   16 SDA 17 DDC/CEC 18 +5V   19 Hot Swap Test          

As shown in the figure above, there are 19 HDMI pins, of which 1-9 pins are data signals;10, 11 and 12 hands are clock signals;13 were CEC needles;14 stitches were empty;15 SCL needles;16 needles were SDA needles;17 needle for the ground;18 pin +5V power supply; Nineteen needles were hot swapping test.
 

4. Common failure problems and solutions of HDMI transmission products

In daily application, common faults are:

a. Cannot display properly;

b. Compatibility;

c. Signal interruption sometimes no;

d. Signal interruption sometimes no;
 

5. Problem analysis and solution:

1)For the problem of not normal display

The performance of the video can not be displayed normally has "dot not bright", "blue screen", "no signal" and so on, the main reasons are several:

a.Direction reverse, HDMI terminal often directional, divided into Source and Display, that is, the input and output end. If the direction is reversed, it will not be displayed normally.

b.The violent construction damaged the HDMI cable, may not be seen outside, but the internal module or cable has been damaged, so after wiring, "the point is not bright" must be replaced.

c.Some of the "not bright" problems can also be classified as compatibility problems.

2) Compatibility issues

EDID recognition blocked, PIN15/16 of HDMI cable is not working properly. This problem is more complex. It is possible that the power supply of PIN17/18 cannot reach 4.8~5.3V, especially when using HDMI cables for long distances. When the voltage is not up to the standard, the long-distance transmission or the optical and electrical conversion module of the optical cable is insufficient in power supply, and the EDID cannot be identified, resulting in "dot failure". In addition, the signal output terminal does not support the EDID reading and writing function, and it is difficult to identify the EDID. This kind of situation occurs more often in self-organizing computers.

In the case that EDID cannot be recognized above, we can try to use a sinter to solve the problem of EDID, but sometimes it cannot be solved, so we need to replace the device interface that supports EDID function.

The existing 4K@60Hz 4:4:4 uncompressed cable has a bandwidth of 18 gigabytes, but some new devices, which may use HDR, require an additional 5 gigabytes of bandwidth, so the HDMI 2.0 version of the cable will not work properly. The solution is to "turn off" the HDR feature on the device.

3) The signal is broken, intermittently

Reason: Most is wire quality problem, or it is to compare when wiring "rough", or it is cable itself "unqualified" article. But also possible device show card drive problem, if it is show card drive problem is about to update show card, if it is wire rod problem better wire rod.

4) Snow noise, white lines

Reason most is concerned with the quality of wire itself, this changes a line to solve directly.

 

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