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We usually see logos that support VGA / HDMI / DisplayPort on the monitor, which are actually the names of video interfaces. Today we will introduce the video interface.

Classification of video interface the main function of video interface is to output video signals to external devices, or to collect collected video signals. According to the type of video signal, a variety of video interfaces can be divided into analog interface and digital interface. The appearance of common video interface is shown in the table below.

Interface name

Interface appearance analog interface AV interface

BNC interface

VGA interface

S terminal interface

Digital interface DVI-I interface

DVI-D interface

HDMI interface

DisplayPort interface

Which of the above video interfaces have you used?

Video interface has experienced the process from analog video interface to digital video interface. Because of the limited data transmission rate, analog video interface can not meet the needs of high-definition video transmission, so it has been replaced by digital video interface. Video interface has been washed out by the market, and most of the video interface has been eliminated. At present, HDMI interface and DisplayPort interface are more common in electronic devices.

So, which of these two interfaces is better or worse, which will win in the final competition and become the ultimate winner of the video interface, we might as well start with the history of the two.

The history of video interface is DVI (Digital Visual Interface) interface in the market before HDMI. DVI is a digital display interface standard issued by the Digital display working Group (Digital Display Working Group,DDWG) composed of Intel, IBM, Silicon Image, HP, Compaq, Fujitsu, NEC and other companies. The purpose is to improve the picture quality of display equipment through standardized digital transmission. There are two types of DVI interfaces:

DVI-D (Digital, pure digital) interface can only receive digital signals. There are only 24 pins in 3 rows and 8 columns on the interface, of which one pin in the upper right corner is empty and it is not compatible with analog signals.

DVI-I (Inteface, universal interface, compatible with VGA signal through adapter) interface, can be compatible with both analog (which can output analog signal through a DVI-I to VGA adapter) and digital signal. This interface has been used in graphics cards, LCD monitors and projectors.

Due to the large size and limited bandwidth of DVI interface, seven companies, Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson and Toshiba, gathered together in April 2002 to establish the organization of HDMI HD multimedia interface. Since December 2002, HDMI standards have been issued continuously. Both audio and video can be transmitted through the HDMI interface, and it has the potential to upgrade, but the problem is that it requires an annual fee of $10, 000 to use it.

Another standardization association, the VESA Association, is not to be outdone. The VESA Association, Video Electronics Standards Association (Video Electronic Standards Association), is an international, non-profit standards association made up of more than 280hardware, software, computer, display and component manufacturers. VESA Association has been issuing DisplayPort (DP) standard since May 2006, which is free of annual fee.

The two standards are tit-for-tat, constantly upgrading their respective performance indicators, since then the video interface field has entered an era of two men competing for hegemony. The development of HDMI and DisplayPort is shown in the figure below.

Basic principles next let's take a look at the principles of HDMI and DisplayPort.

HDMIHDMI is mainly composed of transmitter and receiver. HDMI has three communication channels: display data Channel (DDC), TMDS and CEC, as shown in the figure.

DDC implements to obtain the E. EDID data structure of the receiver at the source side to understand the audio / video format it can adopt.

The three data channels of TMDS can send and receive audio / video information and auxiliary information.

CEC channel implements some high-level user functions, such as infrared remote control.

HDMI has five types of connectors: a, B, C, D and E. Class An is the most common connector, and the pins are shown in the figure.

The definition of the HDMI pin is shown in the following table.

Pin No defines the channels of 1TDMS Data2+2TDMS Data2 Shield3TDMS Data2-4TDMS Data1+5TDMS Data1 Shield6TDMS Data1-7TDMS Data0+8TDMS Data0 Shield9TDMS Data0-10TDMS Clock+11TDMS Clock Shield12TDMS Clock-13CEC14Reserved (N.C. on device) 15SCL16SDA17DDC/CEC Ground18+5V19Hot Plug DetectDisplayPortDisplayPort as consisting of primary links, secondary channels, and hot-plug detection signal lines, as shown in the figure.

The primary link is a unidirectional, high-bandwidth, low-latency channel for transmitting high-speed data, such as synchronous data streams without compressed video or audio.

The auxiliary channel is a half-duplex two-way channel for link management and device control.

The hot plug detection signal line signal line is used by the sending end equipment to detect the hot plug status of the receiving end equipment, and the receiving end equipment sends an interrupt request to the sending end device, etc.

The pin of the DisplayPort is shown in the figure.

The definition of the DisplayPort signal source pin is shown in the following table.

Pin No defines 1ML_Lane 0 + 2GND3ML_Lane 0-4ML_Lane 1 + 5GND6ML_Lane 1-7ML_Lane 2 + 8GND9ML_Lane 2-10ML_Lane 3 + 11GND12ML_Lane 3-13CONFIG114CONFIG215AUX CH+16GND17AUX CH-18Hot Plug19Return DP Power20DP Power comparison so what are the similarities and differences between HDMI and DisplayPort? The radar image compared by HDMI and DisplayPort is shown in the following figure.

Content protection all HDMI versions use high-bandwidth digital content protection technology, or HDCP:High-bandwidth Digital Content Protection, to encrypt link data and provide content protection. DisplayPort adopts content anti-copy protocol AES technology, which provides a key length of up to 2048 bits, and the protection technology is more reliable than HDMI.

Bandwidth performance HDMI 2.1Standard bandwidth reaches 48 Gbps and supports a single 8K (7680 × 4320) display @ 60Hz / 4:2:0/12bit. On the other hand, the bandwidth of DisplayPort 2.0 reaches 77.37 Gbps, which can support video output of 16 K 60 Hz.

Data Control / Auxiliary Channel HDMI version has a consumer electronics control (CEC) low-speed control channel, and the CEC channel is used to transmit commands such as play, stop, fast forward between devices. HDMI version 1.4 adds a differential pair as an audio return channel and an Ethernet channel.

DisplayPort uses an auxiliary channel (AUX) as a two-way communication bus between devices, which has much more bandwidth than CEC. The channel has a bandwidth of 1 Mbps in DisplayPort versions 1.0 and 1.1, and has been increased to 720 Mbps in version 1.2 to support USB and Ethernet. The auxiliary channel can be directly used as the transmission channel of low-bandwidth data such as voice and video, and can also be used for game control without delay.

HDMI interface is more popular than DisplayPort interface in electronic devices in daily life. HDMI interface is widely used in TV, projector and set-top box, while DisplayPort interface is widely used in PC field and high-end display field.

With its first-mover advantage, HDMI has an absolute advantage in consumer-grade devices, while DisplayPort relies on technological advantages to gain ground in some areas of computer and professional design. With the continuous improvement of bandwidth and transmission rate, the two major video interface standards, HDMI and DisplayPort, can be expected to continue to be duo for a long time in the future, bringing a better HD video experience to consumers.

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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