DDC edid Introduction

From: http://blog.csdn.net/hello_wyq/article/details/1337754

1. Introduction: DDC is a bus standard for communications between a display and a computer host. Its full name is display data chnnel. Its basic function is to display the electronic file information of the display, such as the field frequency range that can be received, manufacturer, production date, product serial number, product model, standard display mode and its parameters, supported DDC standard category, and edid version information. The DDC Standard Bus of a higher version also allows the computer host to directly adjust basic parameters of the display, such as brightness, contrast, large or small field range, center location of the line field, and color temperature.

2. DDC bus standard category:

1) ddc1: one-way transmission, clocked by vsync, only transmit standard data information of 128 byte edid.

2) ddc2b: one-way transmission (Address: 0xa0/A1), is a simple standard I2C protocol for reading data from memory, its direction is from the monitor to the Computer Host.

3) ddc2bi: bidirectional transmission, I2C slave mode, transmission of graphical information (address: 0x6e/6f, 0x50/51), supports simple access. Bus standard.

4) ddc2b +: bidirectional transmission, point-to-point, does not support access. Bus, transmission of edid/vdif standard data information (address: 0x6e/6f, 0x50/51 ).

5) ddc2ab: bidirectional transmission, supporting access. Bus and transmitting standard edid/vdif data (Address: 0x6e/6f, 0x50/51 ).

6)

3. edid Data Standard: edid (Extended display identification data standard) is the standard data information that the display transmits to the computer host through DDC. It has been released to the third version, that is, edid version 3, the previous versions include edid Version 1.0, Revision 0, edid version 1, Revision 1, edid version 2, Revision 0, edid version 2, and Revision 1. Edid is divided into 128 bytes and 256 bytes based on the amount of data information. In the future, there may be a new version of edid with more data information.

4. edid data structure introduction: Take the edid of 128 byte as an example, as shown in the following table.

 

No.		Description
8	Bytes	Header
10	Bytes	Vendor/product identification
2	Bytes	Edid version/revision level
15	Bytes	Basic display parameters/Features
19	Bytes	Established/standard timings
72	Bytes	Detailed timing descriptions (18 bytes each) and/or monitor descriptions (18 bytes each)
1	Byte	Extension flag
1	Byte	Checksum

For detailed definitions of each byte and each bit, see the edid Data Protocol definition standard.

5. DDC function implementation: For a display product, to have the plug-and-play DDC function, you must make early planning during product development, otherwise, it will be too late to consider the product development. In general, there are two ways to implement DDC functions. One is to use dedicated hardware IC (such as 24lc21), which is simple and easy to implement, and the quality is also easy to control, however, it will only increase the pressure on hardware costs. The other method is to implement it in a software-only manner. This method has almost no hardware cost considerations, but it is relatively difficult to implement technologies, it requires software designers to have a good understanding of DDC and edid standards. Most of the current displays on the market are supported by ddc1/ddc2b. The higher version of the DDC standard is not frequently used, and the cost is a little higher, and the technology is relatively complicated, so few people do it.

6. Importance of the DDC function: for a single monitor, whether or not it has the same DDC function, it seems to be the same for general users. In fact, for a DDC-enabled display, the Windows operating system will capture the product attribute information at the initial startup, and then optimize the configuration based on the information, the basic information of the manufacturer is displayed. In a Windows operating system, you can adjust the display mode of the system as needed, and tell the user that the display is a plug-and-play display, this is indirectly a publicity for the manufacturer, which is convenient for users. For a display without the DDC function, it does not have all of the above convenience functions and can only be used as an unrecognized monitor. In addition, a DDC-capable display also represents the strength and technical level of product developers. It will win people's trust in the market and contribute to the establishment of its own brand.

DDC history:

VESA display data channel

History

• DDC version 1-August 1994

• DDC version 2-rjl 1996

• DDC version 2.1-July 1996

• DDC Version 3-December 1997 • DDC/ci-August 1998

• Enhanced DDC version 1-Sept. 1999

Http://www.vesa.org/public/PT03EDID.pdf

For details about DVI/hdmi ddc/HDCP, see:

Research on the working principle of DVI and Its Application in digital TV

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