Various types of monitor cables available:
The Digital Visual Interface (DVI) is a display interface developed in response to the proliferation of digital flat-panel displays. For the most part, these displays are currently connected to an analog video graphics array (VGA) interface and, thus, require a double conversion. The digital signal from the computer must be converted to an analog signal for the analog VGA interface, then converted back to a digital signal for processing by the flat-panel display. This inherently inefficient process takes a toll on performance and video quality and adds cost. In contrast, when a flat-panel display is connected to a digital interface, no digital-to-analog conversion is required. The DVI interface is becoming more prevalent and is expected to become widely used for digital display devices, including flat-panel displays and emerging digital CRTs. This article reviews the DVI standard, discusses its current status in the market, and its future prospects.
A number of digital interfaces already exist, but none has emerged as an industry standard. Current portable systems use a low voltage differential signaling (LVDS) digital interface to the liquid crystal display (LCD) panel, but this technology does not transition well to external desktop displays. Other digital interfaces-Digital Flat Panel (DFP), VESAR Plug and Display, and OpenLDI-have also failed to achieve widespread acceptance. In contrast, DVI is widely expected to become the standard digital interface for flat panels. The specification was developed by the Digital Display Working Group (DDWG), which was formed to develop a universal standard for attaching a flat-panel display to a PC. The resulting specification was published in April 1999 and graphics cards with standards-based DVI connectors are now available.
DVI uses Silicon Image's PanelLink, a high-speed serial interface that uses transition minimized differential signaling (TMDS) to send data to the monitor. The DFP and VESA Plug and Display interfaces also use PanelLink. For this reason, DVI can work with these previous interfaces by using adapter cables (depending on the signal quality of the adapter.) TMDS conveys data by transitioning between "on" and "off" states. An advanced encoding algorithm that uses Boolean exclusive OR (XOR) or exclusive NOR (XNOR) operations is applied to minimize the transitions. Minimizing transitions avoids excessive electromagnetic interference (EMI) levels on the cable. An additional operation is performed to balance the DC signal. Figure 1 shows the flow of display (or pixel) data from the graphics controller through TMDS mechanisms (implemented in a chip on the graphics card or in the graphics chip set) and the display controller. In this process, incoming 8-bit data is encoded into 10-bit transition-minimized, DC-balanced characters. (The first eight bits are the encoded data; the ninth bit identifies whether the data was encoded with XOR or XNOR logic; the tenth bit is used for DC balancing.)
