Display data channel

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The Display Data Channel ( DDC ) is a serial communication interface between the monitor and the PC , which enables data to be exchanged via the monitor cable and allows the operating system to automatically install and configure the monitor driver ( plug & play ).

In order to be able to exchange information, the graphics card , cable and monitor must support this data channel. In addition to the analog VGA connection , DDC is also common with the digital visual interface (DVI) and high definition multimedia interface (HDMI). In the case of video interfaces that go beyond this, such as DisplayPort, there are similar interfaces with similar objectives.

The Video Electronics Standards Association (VESA) has issued the following versions of this industry standard :

DDC1

DDC1 (Version 1) comprises the repeated transmission of the Extended Display Identification Data (EDID) from the monitor to the graphics card. The 128 bytes of the EDID data structure contain information on VESA standard compatibility and DPMS support. The data is output as a clock signal with vertical image synchronization, which allows bit rates of 60 bps to 100 bps. The less widespread DDC1 standard is supported by a few analog VGA cathode ray tube monitors .

DDC2B

DDC2B (Version 2 Level B) enables the bidirectional transmission of the VESA Display Identification File (VDIF). The monitor can thus respond to special requests from the graphics card. Technically, an I²C interface is used for this, the monitor is operated as an I²C slave and the graphics card is the I²C master. The I²C address, functionally implemented as a serial I²C EEPROM , is set to the value 0x50 in the monitor. The EDID data block is located in the first 128 bytes of the I²C memory in the monitor and is read out by the graphics card.

As a special feature, the power supply comes from the graphics card, i. H. In addition to the I²C data line (SDA), I²C clock line (SCL) and ground (GND), the graphics card supplies a supply voltage of +5 V with a maximum of 50 mA, which then allows the I²C memory module to be used to query the monitor data when the monitor is turned off or unplugged.

DDC2AB

In addition to the DDC2B, additional data is held in a larger memory beyond the first 128 bytes of EDID data. The data transfer rate has increased to 100 kbps.

DDC / CI

DDC / CI stands for Display Data Channel / Command Interface and was introduced in August 1998. In addition to querying monitor information, it also allows the monitor to be controlled, i.e. the settings that can otherwise only be changed via the on-screen display on the monitor. The control takes place via the Monitor Control Command Set (MCCS).

Web links

Software for controlling monitors that support the DDC / CI protocol:

Individual evidence

  1. ↑ Display Data Channel Command Interface (DDC / CI) standard. VESA, accessed June 13, 2016 .