![]() ![]() The DDC signal can be sent to or from a video graphics array (VGA) monitor with the I 2C protocol using the master's serial clock and serial data pins.ĭDC1 is a simple, low-speed, unidirectional serial link protocol. However, during the transition, the change was not backwards-compatible and video cards using the old scheme could have problems if a DDC-capable monitor was connected. ĭDC changed the purpose of the ID pins to incorporate a serial link interface. More elaborate schemes also existed that used all of the 4 ID pins while manipulating the HSync and VSync signals in order to extract 16 bits (4 ID pin values for each of the 4 combinations of HSync and VSync states) of monitor identification. In this scheme, the input states of the ID pins would encode the monitor type as follows: ID2 (pin 4) Finally, the ID2 pulled to GND signaled a monitor capable of 1024×768 resolution, such as IBM 8514. The ID0 was pulled to GND by color monitors, while the monochrome monitors pulled ID1 to GND. In the most commonly documented scheme, the ID3 pin was unused and only the 3 remaining pins were defined. These ID pins, attached to resistors to pull one or more of them to ground (GND), allowed for the definition of the monitor type, with all open (n/c, not connected) meaning "no monitor". Prior to the DDC, the VGA standard had reserved four pins in the analog VGA connector, known as ID0, ID1, ID2 and ID3 (pins 11, 12, 4 and 15) for identification of monitor type. The DDC standard has been superseded by E-DDC in 1999. It included the EDID 1.0 format and specified DDC1, DDC2B and DDC2Ab physical links.ĭDC version 2, introduced in April 1996, split EDID into a separate standard and introduced the DDC2B+ protocol.ĭDC version 3, December 1997, introduced the DDC2Bi protocol and support for VESA Plug and Display and Flat Panel Display Interface on separate device addresses, requiring them to comply with EDID 2.0. ![]() The first version of the DDC standard was adopted in August 1994. The most current version is Enhanced EDID (E-EDID) Release A, v2.0. The format uses a description block containing 128 bytes of data, with optional extension blocks to provide additional information. The DDC suite of standards aims to provide Plug and Play and DPMS power management experiences for computer displays.ĭDC1 and DDC2B/Ab/B+/Bi protocols are a physical link between a monitor and a video card, which was originally carried on either two or three pins in a 15-pin analog VGA connector.Įxtended display identification data (EDID) is a companion standard it defines a compact binary file format describing the monitor's capabilities and supported graphics modes, stored in a read-only memory ( EEPROM) chip programmed by the manufacturer of the monitor. The standard was created by the Video Electronics Standards Association (VESA). ![]() Like modern analog VGA connectors, the DVI and DisplayPort connectors include pins for DDC, but DisplayPort only supports DDC within its optional Dual-Mode DP ( DP++) feature in DVI/HDMI mode. The Display Data Channel, or DDC, is a collection of protocols for digital communication between a computer display and a graphics adapter that enable the display to communicate its supported display modes to the adapter and that enable the computer host to adjust monitor parameters, such as brightness and contrast. ( August 2022) ( Learn how and when to remove this template message) Several templates and tools are available to assist in formatting, such as Reflinks ( documentation), reFill ( documentation) and Citation bot ( documentation). Please consider converting them to full citations to ensure the article remains verifiable and maintains a consistent citation style. This article uses bare URLs, which are uninformative and vulnerable to link rot. ![]()
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